Articles

Els filtres actuals son: Any inici = 2016, Any final = 2017
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Aparicio F.L., Nieto-Cid M., Calvo E., Pelejero C., López-Sanz A., Pascual J., Salat J., Sánchez-Pérez E.D., De La Fuente P., Gasol J.M., Marrasé C. (2017)
Science of The Total Environment, 609, 1001-1012. DOI: 10.1016/j.scitotenv.2017.07.170. (BibTeX: aparicio.etal.2017)
Resum: Veure
Marine biogeochemistry dynamics in coastal marine areas is strongly influenced by episodic events such as rain, in- tense winds, river discharges and anthropogenic activities. We evaluated in this study the importance of these forc- ing events on modulating seasonal changes in the marine biogeochemistry of the northwestern coast of the Mediterranean Sea, based on data gathered from a fixed coastal sampling station in the area. A 4-year (2011– 2014) monthly sampling at four depths (0.5 m, 20 m, 50 m and 80 m) was performed to examine the time variability of several oceanographic variables: seawater temperature, salinity, inorganic nutrient concentrations (NO−3 , PO34− and SiO2), chlorophyll a (Chl a), dissolved organic carbon (DOC) and fluorescent dissolved organic matter (FDOM). FDOM dynamics was predominantly influenced by upwelling events and mixing processes, driven by strong and characteristic wind episodes. SW wind episodes favored the upwelling of deeper and denser waters into the shallower shelf, providing a surplus of autochthonous humic-like material and inorganic nutrients, whereas northerlies favored the homogenization of the whole shelf water column by cooling and evaporation. These different wind-induced processes (deep water intrusion or mixing), reported along the four sampled years, determined a high interannual environmental variability in comparison with other Mediterranean sampling sites.
Paraules clau: NW Mediterranean Wind events Salinity Inorganic nutrients DOC FDOM
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Barella-Ortiz A., Polcher J., de Rosnay P., Piles M., Gelati E. (2017)
Hydrology and Earth System Sciences, 21, 357-375. DOI: 10.5194/hess-21-357-2017. (BibTeX: barellaortiz.etal.2017a)
Resum: Veure
L-band radiometry is considered to be one of the most suitable techniques to estimate surface soil moisture (SSM) by means of remote sensing. Brightness temperatures are key in this process, as they are the main input in the retrieval algorithm which yields SSM estimates. The work exposed compares brightness temperatures measured by the SMOS mission to two different sets of modelled ones, over the Iberian Peninsula from 2010 to 2012. The two modelled sets were estimated using a radiative transfer model and state variables from two land-surface models: (i) ORCHIDEE and (ii) H-TESSEL. The radiative transfer model used is the CMEM. Measured and modelled brightness temperatures show a good agreement in their temporal evolution, but their spatial structures are not consistent. An empirical orthogonal function analysis of the brightness temperature’s error identifies a dominant structure over the south-west of the Iberian Peninsula which evolves during the year and is maximum in autumn and winter. Hypotheses concerning forcing-induced biases and assumptions made in the radiative transfer model are analysed to explain this inconsistency, but no candidate is found to be responsible for the weak spatial correlations at the moment. Further hypotheses are proposed and will be explored in a forthcoming paper. The analysis of spatial inconsistencies between modelled and measured TBs is important, as these can affect the estimation of geophysical variables and TB assimilation in operational models, as well as result in misleading validation studies.
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Belmonte M., Stoffelen A., Verspeek J., Verhoef A., Neyt X., Anderson C. (2017)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10, 5, 2195 - 2204. DOI: https://doi.org/10.1109/JSTARS.2017.2647842. (BibTeX: belmonte.etal.2017)
Resum: Veure
With an eye on the generation of a long-term climate record of ocean winds, soil moisture and sea ice extents across the C-band ERS and ASCAT scatterometer spans, a new calibration tool termed cone metrics has been developed. The new method is based on monitoring changes in the location and shape of the surface of maximum density of ocean backscatter measurements, also known as “the wind cone”. The cone metrics technique complements established calibration approaches, such as rain forest and NWP ocean calibration, through the characterization of linear as well as non-linear beam offsets, the latter via wind cone deformations. Given instrument evolution, proven stability and the monitoring by transponders, we take ASCAT-A data over 2013 as absolute calibration reference. This paper describes the new method and its application as inter- calibration tool in the context of the reprocessing activities for ERS-1 and ERS-2. Cone metrics succeeds at establishing the linear and non-linear corrections necessary to homogenize the ASCAT and ERS C-band records down to 0.05 dB.
Paraules clau: Radar signal processing, calibration, antenna radiation pattern.
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Casanova-Masjoan M., Pelegrí J.L., Sangrà P., Martínez A., Grisolía-Santos D., Pérez-Hernández M.D., Hernández-Guerra A. (2017)
Journal of Geophysical Research: Oceans, 122, 9, 7049-7065. DOI: 10.1002/2017JC012969. (BibTeX: casanovamasjoan.etal.2017)
Resum: Veure
A South Atlantic ring is studied through remote sensing altimetry, hydrographic stations, and drifters’ trajectories. The ring’s core was characterized by warmer and saltier Indian Ocean waters. At the time of the cruise, the ring’s signature extended radially out to 124 km and vertically down to 2000 m, and its core absolute dynamic topography (ADT) exceeded the surrounding Atlantic Ocean waters in 0.4 m. The geo- strophic velocities were anticyclonic with maximum speeds about 35 cm s21 at 100 m and reaching negligible values near 4500 m. The rotational transport inside the ring was 33 Sv in the thermocline and intermediate layers. The drifters’ data distinguish a 30-km core revolving as a solid body with periodicity near 5 days and a transitional band that revolves with constant tangential velocity, resembling a Rankine vortex. The ADT data identify the ring’s track, showing that it was shed by the Agulhas Current retroflection in November 2009 and propagated northwest rapidly during the first 2 months (mean speed of about 10 cm s21) but slowed down substantially (3–4 cm s21) between March and July 2010, when it was last detected. The altimetry data also outlines the evolution of the ring’s core ADT, radius, vorticity, and, through a simple calibration with the cruise data, rotational transport. In particular, the ring surface and vertical-mean vorticity decay with time scales of 373 and 230 days, respectively, indicating that most of the property anomalies contained by the ring are dif- fused out to the subtropical gyre before it reaches the western boundary current system.
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Dall’Osto M., Ovadnevaite J., Paglione M., Beddows D.C.S., Ceburnis D., Cree C., Cortés P., Zamanillo M., Nunes S.O., Pérez G.L., Ortega-Retuerta E., Emelianov M., Vaqué D., Marrasé C., Estrada M., Sala M.M., Vidal M., Fitzsimons M.F., Beale R., Airs R., Rinaldi M., Decesari S., Facchini M.C., Harrison R.M., O’Dowd C., Simó R. (2017)
Scientific Reports, 7, 6047, 1-10. DOI: 10.1038/s41598-017-06188-x. (BibTeX: dallosto.etal.2017a)
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Gabarro C., Turiel A., Elósegui P., Pla-Resina J., Portabella M. (2017)
The Cryosphere, 11, 1987-2002. DOI: 10.5194/tc-11-1987-2017. (BibTeX: gabarro.etal.2017)
Resum: Veure
Monitoring sea ice concentration is required for operational and climate studies in the Arctic Sea. Technolo- gies used so far for estimating sea ice concentration have some limitations, for instance the impact of the atmosphere, the physical temperature of ice, and the presence of snow and melting. In the last years, L-band radiometry has been suc- cessfully used to study some properties of sea ice, remark- ably sea ice thickness. However, the potential of satellite L- band observations for obtaining sea ice concentration had not yet been explored. In this paper, we present preliminary evidence showing that data from the Soil Moisture Ocean Salinity (SMOS) mission can be used to estimate sea ice concentration. Our method, based on a maximum-likelihood estimator (MLE), exploits the marked difference in the radiative properties of sea ice and seawater. In addition, the brightness temperatures of 100 % sea ice and 100 % seawater, as well as their com- bined values (polarization and angular difference), have been shown to be very stable during winter and spring, so they are robust to variations in physical temperature and other geo- physical parameters. Therefore, we can use just two sets of tie points, one for summer and another for winter, for cal- culating sea ice concentration, leading to a more robust esti- mate. After analysing the full year 2014 in the entire Arctic, we have found that the sea ice concentration obtained with our method is well determined as compared to the Ocean and Sea Ice Satellite Application Facility (OSI SAF) dataset. How- ever, when thin sea ice is present (ice thickness 0.6 m), the method underestimates the actual sea ice concentration. Our results open the way for a systematic exploitation of SMOS data for monitoring sea ice concentration, at least for specific seasons. Additionally, SMOS data can be synergisti- cally combined with data from other sensors to monitor pan- Arctic sea ice conditions.
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García-Olivares A., Agüero A., Haupt B.J., Marcos M.J., Villar M.V., de Pablos J.L. (2017)
Science of The Total Environment, 593-594, 242-252. DOI: 10.1016/j.scitotenv.2017.03.152. (BibTeX: garciaolivares.etal.2017c)
Resum: Veure
Worldwide tank spills represent 10% of the average annual input of oil in the sea. When such spills arise from wrecks at depth, neutralisation of environmental impacts is difficult to achieve. Extracting oil from sunken tankers is expensive, and, unfortunately, all of the oil cannot be extracted, as the Prestige case demonstrates. We propose an environmentally appropriate, cost-effective and proactive method to stop the long-term problem of leaks from sunken tankers similar to the Prestige. This method confines the wreck with a “sediment” capping of sepiolite mineral that emulates a natural sediment. A set of experiments and simulations shows that sepiolite has the characteristics necessary to accomplish the confinement of any current or future sunken tanker with minimal environmental perturbation.
Paraules clau: Oil spills, sunken tankers, environmental impact, confinement, sepiolite
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Gasser M., Pelegrí J.L., Emelianov M., Bruno M., Gràcia E., Pastor M., Peters H., Rodríguez-Santana A., Salvador J., Sánchez-Leal R.F. (2017)
Progress in Oceanography, 157, 47-71. DOI: 10.1016/j.pocean.2017.05.015. (BibTeX: gasser.etal.2017)
Resum: Veure
The Mediterranean Water leaves the western end of the Strait of Gibraltar as a bottom wedge of salty and warm waters flowing down the continental slope. The salinity of the onset Mediterranean Outflow Water (MOW) is so high that leads to water much denser (initially in excess of 1.5 kg m 3) than the overlying central waters. During much of its initial descent, the MOW retains large salinity anomalies – causing density anomalies that induce its gravity current character – and relatively high westward speeds – caus- ing a substantial Coriolis force over long portions of its course. We use hydrographic data from six cruises (a total of 1176 stations) plus velocity data from two cruises, together with high-resolution bathymetric data, to track the preferential MOW pathways from the Strait of Gibraltar into the western Gulf of Cadiz and to examine the relation of these pathways to the bottom topography. A methodology for tributary systems in drainage basins, modified to account for the Coriolis force, emphasizes the good agreement between the observed trajectories and those expected from a topographically-constrained flow. Both contour avenues and cross-slope channels are important and have complementary roles steering the MOW along the upper and middle continental slope before discharging as a neutrally buoyant flow into the western Gulf of Cadiz. Our results show that the interaction between bottom flow and topography sets the path and final equilibrium depths of the modern MOW. Furthermore, they support the hypoth- esis that, as a result of the high erosive power of the bottom flow and changes in bottom-water speed, the MOW pathways and mixing rates have changed in the geological past.
Paraules clau: Mediterranean outflow water Strait of Gibraltar Gulf of Cadiz Topographic steering Bottom drainage system Along-slope contour avenues Down-slope erosional channels
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Isern-Fontanet J., Ballabrera-Poy J., Turiel A., García-Ladona E. (2017)
Nonlinear Processes in Geophysics, 24, 613-643. DOI: 10.5194/npg-24-613-2017. (BibTeX: isernfontanet.etal.2017)
Resum: Veure
Ocean currents play a key role in Earth’s climate – they impact almost any process taking place in the ocean and are of major importance for navigation and human ac- tivities at sea. Nevertheless, their observation and forecasting are still difficult. First, no observing system is able to provide direct measurements of global ocean currents on synoptic scales. Consequently, it has been necessary to use sea surface height and sea surface temperature measurements and refer to dynamical frameworks to derive the velocity field. Second, the assimilation of the velocity field into numerical models of ocean circulation is difficult mainly due to lack of data. Recent experiments that assimilate coastal-based radar data have shown that ocean currents will contribute to increasing the forecast skill of surface currents, but require application in multidata assimilation approaches to better identify the thermohaline structure of the ocean. In this paper we review the current knowledge in these fields and provide a global and systematic view of the technologies to retrieve ocean ve- locities in the upper ocean and the available approaches to assimilate this information into ocean models.
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Jordà G., Von Schuckmann K., Josey S.A., Caniaux G., García-Lafuente J., Sammartino S., Özsoy E., Polcher J., Notarstefano G., Poulain P.M., Adloff F., Salat J., Naranjo C., Schroeder K., Chiggiato J., Sannino G., Macías D. (2017)
Progress in Oceanography, 156, 174-208. DOI: 10.1016/j.pocean.2017.07.001. (BibTeX: jorda.etal.2017)
Resum: Veure
This paper presents a review of the state-of-the-art in understanding and quantification of the Mediterranean heat and mass (i.e. salt and water) budgets. The budgets are decomposed into a basin averaged surface component, lateral boundary components (through the Gibraltar and the Dardanelles Straits), a river input component and a content change component. An assessment of the different meth- ods and observational products that have been used to quantify each of these components is presented. The values for the long term average of each component are also updated based on existing literature and a first estimate of heat fluxes associated with the riverine input has been produced. Special emphasis is put on the characterization of associated uncertainties and proposals for advancing current knowledge are presented for each budget component. With the present knowledge of the different components, the Mediterranean budgets can be closed within the range of uncertainty. However, the uncertainty range remains relatively high for several terms, particularly the basin averaged surface heat fluxes. Consequently, the basin averaged heat budget remains more strongly constrained by the Strait of Gibraltar heat transport than by the surface heat flux. It is worth remarking that if a short ($few years) averaging period is used, then the heat content change must also be considered to constrain the heat budget. Concerning the water and salt fluxes, the highest uncertainties are found in the direct estimates of the Strait of Gibraltar water and salt transport. Therefore, the indirect estimate of those transports using the budget closure leads to smaller uncertain- ties than the estimates based on direct observations. Finally, estimates of Mediterranean heat and salt content trends are also reviewed. However, these cannot be improved through the indirect estimates due to the large temporal uncertainties associated to the surface fluxes and the fluxes through Gibraltar. The consequences of these results for estimates of the Mediterranean temperature and salinity trends obtained from numerical modelling are also considered.
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Lang S., Lin W. (2017)
Journal of Ocean Technology, 36, 1, 19-23. DOI: 10.3969/j.issn.1003-2029.2017.01.004. (BibTeX: lang.lin.2017)
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Lin W., Portabella M., Stoffelen A., Verhoef A. (2017)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10, 5, 2156-2164. DOI: 10.1109/JSTARS.2016.2616889. (BibTeX: lin.etal.2017)
Resum: Veure
The sea-surface winds from the RapidScat scatterometer (RSCAT) onboard the International Space Station (ISS) have been produced using the Pencil-beam scatterometer Wind Processor (PenWP) since December 2014. An inversion residual or Maximum Likelihood Estimator (MLE-) based quality control (QC) algorithm is included in PenWP to distinguish between good- and poor-quality winds.Generally, the QC-accepted RSCAT winds are in good agreement with both the Advanced Scatterometer (ASCAT) winds and the European Centre for Medium-range Weather Forecasting (ECMWF) model output. In contrast, the QC-rejected winds present an overall positive bias with respect to ASCAT and ECMWF winds, mainly due to the impact of rain. However, it has been recently found that a considerable portion (>5%) of RSCAT QC-rejected contains anomalously low retrieved speeds (w< 4 m/s) under medium or high wind conditions (w > 10 m/s) according to ASCAT/ECMWF. This paper attempts to sort out the cause for these spuriously low winds. A revised MLE inversion with prefiltering the anomalous backscatters is proposed to correct the mentioned inversion issue. The impact of such improved inversion on the retrieved RSCAT winds is evaluated using both the collocated ASCAT and ECMWF winds.The results show that the proposed algorithm improves the wind retrieval of the spuriously low wind cases remarkably, while preserving about 4.7% of the nominal QC-rejected data (0.25% in total).
Paraules clau: Anomalous backscatter, low winds, quality control, rapidScat scatterometer, wind inversion.
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Lin W., Portabella M. (2017)
IEEE Transactions on Geoscience and Remote Sensing, 55, 7, 3922-3930. DOI: 10.1109/TGRS.2017.2683720. (BibTeX: lin.portabella.2017)
Resum: Veure
Quality control (QC) is an essential part of the scatterometer wind retrieval. In the current pencil-beam scatterometer wind processor (PenWP), a maximum likelihood estimator (MLE)-based QC is used to discern between good- and poor-quality winds. MLE QC is generally effective in flagging rain contamination and increased subcell wind variability in the ocean surface wind vectors derived from Ku-band pencilbeam scatterometers, such as the RapidScat (RSCAT) installed on the International Space Station. However, the MLE is not an effective quality indicator over the outer swath where the inversion is underdetermined due to the lack of azimuthal diversity (including lack of horizontal polarized measurements). Besides, it is challenging to discriminate rain contamination from “true” high winds. This paper reviews several wind qualitysensitive indicators derived from the RSCAT data, such as MLE and its spatially averaged value (MLEm), and the singularity exponents (SE) derived from an image processing technique, called singularity analysis. Their sensitivities to data quality and rain are evaluated using collocated Advanced Scatterometer wind data, and global precipitation measurement satellite’s microwave imager rain data, respectively. It shows that MLEm and SE are the most effective indicators for filtering the poorest-quality winds over RSCAT inner and outer swath, respectively. A simple combination of SE and MLEm thresholds is proposed to optimize RSCAT wind QC. Comparing to the operational PenWP QC, the proposed method mitigates over-rejection at high winds, and improves the classification of good- and poor-quality winds.
Paraules clau: Quality control (QC), rain, scatterometer, singularity analysis (SA), winds.
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Liu L., Dong X., Lin W., Zhu J., Zhu D. (2017)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10, 5, 2372-2382. DOI: 10.1109/JSTARS.2016.2646840. (BibTeX: liu.etal.2017)
Resum: Veure
Various reconstruction methods have been used to enhance the spatial resolution of scatterometer data. Most of the image reconstructions are two-dimensional problems, which combine multiple passes of overlapping data over the temporally homogeneous surface, and thus are only suitable for land and ice applications. This paper attempts to address the one-dimensional reconstruction to enhance the azimuth resolution of scatterometer data using a single pass of observations. Since the range resolution determined by the on-board dechirping technique is generally up to several hundred meters, the one-dimensional reconstruction is adequate for certain near real-time ocean applications, such as the development of coastal scatterometer winds. Three well-known reconstruction algorithms, including additive algebraic reconstruction technique (AART), multiplicative algebraic reconstruction technique (MART), and scatterometer image reconstruction (SIR), are evaluated. The spatial resolution and the reconstruction precision resolved by each algorithm are separately analyzed using the local impulse response andMonte Carlo methods. The dependence of the spatial resolution and the reconstruction precision on a variety of parameters, such as the mean backscatter coefficient and its variance, the beamwidth of spatial response function (SRF), and the SRF function type, is evaluated using a simulation framework. In particular, the tradeoff between the spatial resolution and the reconstruction precision is examined for three algorithms.The results show that SIR offers the quickest convergence and lowest noise.
Paraules clau: Local impulse response, reconstruction algorithms, resolution, scatterometer, spatial response function (SRF).
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Liu L., Dong X., Lin W., Zhu J., Zhu D. (2017)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10, 6, 2702-2712. DOI: 10.1109/JSTARS.2017.2679127. (BibTeX: liu.etal.2017a)
Resum: Veure
A dual-frequency polarized scatterometer (DPSCAT) is proposed for the Chinese Water Cycle Observation Mission (WCOM) to be launched around 2020. DPSCAT is used to mea- sure the snow water equivalent (SWE) and the freeze/thaw state, which requires a measurement precision of 0.5 dB and a relatively higher spatial resolution (2–5 km) than the regular scatterometers (about 25 km). Therefore, the conventional range-gate dechirping along with the Doppler beam sharpening (DBS) technique is used by DPSCAT to achieve high range and azimuth resolution simul- taneously. However, DBS cannot improve the azimuth resolution over the nadir swath; thus, a new data processing, namely regu- larized deconvolution method (RDM), is explored to address this problem. In this paper, a quantitative analysis model is developed for RDM in order to study two crucial issues, i.e., the spatial res- olution (mainly for the nadir swath) and the accuracy/precision of the backscatter measurements after resolution enhancement. Nor- mally, the measurement precision and spatial resolution cannot be improved simultaneously using RDM. The accuracy/precision degrades as the spatial resolution improves, and vice versa. More- over, they both degrade as the measurement noise or uncertainty increases, which latter is usually defined as the normalized stan- dard deviation of the measurements (Kp ). In case of SWE retrieval that requires a reconstructed measurement precision of 0.5 dB, the best spatial resolution resolved by RDM is 3 km for Kp = 7%, 4kmforKp =10%,and5kmforKp =12%.
Paraules clau: Precision, regularized deconvolution method (RDM), resolution enhancement, scatterometer, spatial resolution.
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Mason E., Pascual A., Gaube P., Ruiz S., Pelegrí J.L., Delepoulle A. (2017)
Journal of Geophysical Research: Oceans, 122, 4, 3329-3357. DOI: 10.1002/2016JC012611. (BibTeX: mason.etal.2017)
Resum: Veure
Horizontal and vertical motions associated with coherent mesoscale structures, including eddies and meanders, are responsible for significant global transports of many properties, including heat and mass. Mesoscale vertical fluxes also influence upper ocean biological productivity by mediating the supply of nutrients into the euphotic layer, with potential impacts on the global carbon cycle. The Brazil-Malvinas Confluence (BMC) is a western boundary current region in the South Atlantic with intense mesoscale activity. This region has an active role in the genesis and transformation of water masses and thus is a critical component of the Atlantic meridional overturning circulation. The collision between the Malvinas and Brazil Currents over the Patagonian shelf/slope creates an energetic front that translates offshore to form a vigorous eddy field. Recent improvements in gridded altimetric sea level anomaly fields allow us to track BMC mesoscale eddies with high spatial and temporal resolutions using an automated eddy tracker. We characterize the eddies across fourteen 5° × 5° subregions. Eddy-centric composites of tracers and geostrophic currents diagnosed from a global reanalysis of surface and in situ data reveal substantial subregional heterogeneity. The in situ data are also used to compute the evolving quasi-geostrophic vertical velocity (QG-ω) associated with each instantaneous eddy instance. The QG-ω eddy composites have the expected dipole patterns of alternating upwelling/downwelling, however, the magnitude and sign of azimuthally averaged vertical velocity varies among subregions. Maximum eddy values are found near fronts and sharp topographic gradients. In comparison with regional eddy composites, subregional composites provide refined information about mesoscale eddy heterogeneity.
Paraules clau: mesoscale eddies;vertical velocity;eddy compositing;subregional compositing;Brazil-Malvinas Confluence;quasi-geostrophic omega equation
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Olivar M.P., Hulley P.A., Castellón A., Emelianov M., López C., Tuset V.M., Contreras T., Molí B. (2017)
Progress in Oceanography, 151, 116–137. DOI: 10.1016/j.pocean.2016.12.001. (BibTeX: olivar.etal.2017a)
Resum: Veure
In this investigation we analysed the changes in fish species occurrences and relative abundances across the tropical and equatorial Atlantic, and their vertical distribution patterns in relation to the different environmental scenarios. The study covers a wide region encompassing different water masses, and marked differences in productivity, from an oligotrophic zone close to the Brazilian coast, to a very productive upwelling region close to the Northwest African upwelling. Fishes were collected with a mediumsized midwater trawl (Mesopelagos), complemented by hauls made with a macrozooplankton net (MOCNESS). Species richness in the region was higher than in subtropical, temperate and cold regions. The total number of species and their overall abundance was lower in the stations closer to the Brazilian coast. Abundant species across the entire region were the gonostomatids Cyclothone alba, Cyclothone acclinidens, Cyclothone pallida and Cyclothone pseudopallida, the myctophid Lampanyctus alatus, the sternoptychid Sternoptyx diaphana, and the phosichthyid Vinciguerria nimbaria. The occurrences and abundances of C. parapallida, Lampanyctus nobilis and Lepidophanes guentheri were related to zones where AAIW waters occupied the mesopelagic layers, while other species such as Cyclothone livida and Polyipnus polli increased their abundance when AAIW disappears from their living depths. The presence of Eastern North Atlantic Central Water (ENACW) was associated with the occurrence of several myctophids (Benthosema glaciale, Ceratoscopelus maderensis, Diaphus holti, Diaphus rafinesquii, Hygophum hygomii, Lampanyctus crocodilus, Myctophum punctatum, Symbolophorus veranyi), and the gonostomatid Cyclothone braueri. In spite of the important differences in hydrographic features across the tropical and equatorial Atlantic, all stations showed either the general night migration into the epipelagic layers carried out by myctophids, phosicthyids, and some stomiids, or the presence of the several species of Cyclothone, sternoptychids and melamphaeids that remain in the mesopelagic layers, both day and night. The oxygen minimum zone (OMZ) at mesopelagic depths in the north-eastern sector does not seem to disrupt diel vertical migration. Day-night distributions in our study proved that mesopelagic migratory species are capable of crossing these wide hypoxic layers, and that some species such as Diaphus vanhoeffeni remain in these layers during the day. Other non-migratory fishes (Cyclothone spp. and S. diaphana) proved to be widely tolerant to these low oxygen concentrations, as shown by their high numerical abundances in the OMZ.
Paraules clau: Lanternfishes, lightfishes, hatchetfishes, diel migration, midwater trawls, diversity, zoogeography, water masses
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Olmedo E., Martínez J., Turiel A., Ballabrera-Poy J., Portabella M. (2017)
Remote Sensing of Environment, 193, 103–126. DOI: 10.1016/j.rse.2017.02.023. (BibTeX: olmedo.etal.2017b)
Resum: Veure
The Soil Moisture and Ocean Salinity (SMOS) mission has provided a unique remote sensing capability for observing key variables of the hydrological cycle, such as the Sea Surface Salinity (SSS). However, due to some limitations related to the instrument interferometric concept and its challenging data processing, SMOS SSS maps still display significant artifacts and biases, especially close to the coast, mainly due to the presence of Radio Frequency Interferences (RFI) and Land-sea contamination (LSC). In this paper, a new methodology for filtering salinity retrievals and correcting for spatial biases is introduced and validated.
Paraules clau: Soil moisture and ocean salinity (SMOS) Sea Surface Salinity Salinity retrieval Remote sensing Physical oceanography
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Pérez-Hernández M.D., Hernández-Guerra A., Comas-Rodríguez I., Benítez-Barrios V.M., Fraile-Nuez E., Pelegrí J.L., Naveira-Garabato A.C. (2017)
Ocean Science, 13, 577–587. DOI: 10.5194/os-13-577-2017. (BibTeX: perezhernandez.etal.2017)
Resum: Veure
Decadal differences in the Falkland Plateau are studied from the two full-depth hydrographic data collected during the ALBATROSS (April 1999) and MOC-Austral (February 2010) cruises. Differences in the upper 100 dbar are due to changes in the seasonal thermocline, as the ALBATROSS cruise took place in the austral fall and the MOCAustral cruise in summer. The intermediate water masses seem to be very sensitive to the wind conditions existing in their formation area, showing cooling and freshening for the decade as a consequence of a higher Antarctic Intermediate Water (AAIW) contribution and of a decrease in the Subantarctic Mode Water (SAMW) stratum. The deeper layers do not exhibit any significant change in the water mass properties. The Subantarctic Front (SAF) in 1999 is observed at 52.2–54.8º W with a relative mass transport of 32.6 Sv. In contrast, the SAF gets wider in 2010, stretching from 51.1 to 57.2º W (the Falkland Islands), and weakening to 17.9 Sv. Changes in the SAF can be linked with the westerly winds and mainly affect the northward flow of Subantarctic Surface Water (SASW), SAMW and AAIW/Antarctic Surface Water (AASW). The Polar Front (PF) carries 24.9 Sv in 1999 (49.8–44.4º W), while in 2010 (49.9–49.2º W) it narrows and strengthens to 37.3 Sv.
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Ramírez-Pérez M., Gonçalves-Araujo R., Wiegmann S., Torrecilla E., Bardají R., Röttgers R., Bracher A., Piera J. (2017)
Plos One. Open acces, 12, 1, 1-21. DOI: 10.137 1/journal .pone.017070 6. (BibTeX: ramirezperez.etal.2017b)
Resum: Veure
The detection and prediction of changes in coastal ecosystems require a better understanding of the complex physical, chemical and biological interactions, which involves that observations should be performed continuously. For this reason, there is an increasing demand for small, simple and cost-effective in situ sensors to analyze complex coastal waters at a broad range of scales. In this context, this study seeks to explore the potential of beam attenuation spectra, c(λ), measured in situ with an advanced-technology optical transmissometer, for assessing temporal and spatial patterns in the complex estuarine waters of Alfacs Bay (NW Mediterranean) as a test site. In particular, the information contained in the spectral beam attenuation coefficient was assessed and linked with different biogeochemical variables. The attenuation at λ = 710 nm was used as a proxy for particle concentration, TSM, whereas a novel parameter was adopted as an optical indicator for chlorophyll a (Chl-a) concentration, based on the local maximum of c(λ) observed at the long-wavelength side of the red band Chl-a absorption peak. In addition, since coloured dissolved organic matter (CDOM) has an important influence on the beam attenuation spectral shape and complementary measurements of particle size distribution were available, the beam attenuation spectral slope was used to analyze the CDOM content. Results were successfully compared with optical and biogeochemical variables from laboratory analysis of collocated water samples, and statistically significant correlations were found between the attenuation proxies and the biogeochemical variables TSM, Chl-a and CDOM. This outcome depicted the potential of high-frequency beam attenuation measurements as a simple, continuous and cost-effective approach for rapid detection of changes and patterns in biogeochemical properties in complex coastal environments.
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Salat J., Lavín A., González-Pola C., Vélez-Belchí P., Sánchez R., Vargas-Yáñez M., García-Lafuente J., Marcos M., Gomis D. (2017)
CLIVAR Exchanges, 73, 32-38. (BibTeX: salat.etal.2017a)
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Sánchez E., Rodríguez B., Bladé I., Brunet M., Aznar R., Cacho I., Casado M.J., Gimeno L., Gutiérrez J.M., Jordá G., Lavín A., López J.A., Salat J., Valero B. (2017)
CLIVAR Exchanges, 73, 1-4. (BibTeX: sanchez.etal.2017b)
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Stoffelen A., Aaboe S., Calvet J.C., Cotton J., De Chiara G., Figa J., Mouche A., Portabella M., Scipal K., Wagner W. (2017)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 10, 5, 2086-2097. DOI: 10.1109/JSTARS.2017.2696424. (BibTeX: stoffelen.etal.2017)
Resum: Veure
The second-generation exploitation of meteorological satellite polar system (EPS-SG) C-band-wavelength scatterometer instrument (called SCA), planned for launch in 2022, has a direct heritage from the successful advanced scatterometer (ASCAT) flown on the current EPS satellites. In addition, SCA will represent three major innovations with respect to ASCAT, namely: 1) Cross polarization and horizontal copolarization; 2) a nominal spatial resolution of 25 km; and 3) 20% greater spatial coverage than ASCAT. The associated expected science and application benefits that led the SCA design are discussed with respect to ocean, land, and sea ice applications for near-real time, climate monitoring, and research purposes. Moreover, an option to implement an ocean Doppler capability to retrieve the ocean motion vector is briefly discussed as well. In conclusion, the SCA instrument innovations are well set to provide timely benefits in all the main application areas of the scatterometer (winds, soil moisture, sea ice) and can be expected to contribute to new and more sophisticated meteorological, oceanographic, land, sea ice, and climate services in the forthcoming SCA era.
Paraules clau: Eddy currents, radar signal processing, sea ice, soil measurements, storms, wind.
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Vargas-Yáñez M., García-Martínez M.C., Moya F., Balbín R., López-Jurado J.L., Serra M., Zunino P., Pascual J., Salat J. (2017)
Progress in Oceanography, 157, 27-46. DOI: 10.1016/j.pocean.2017.09.004. (BibTeX: vargasyanez.etal.2017)
Resum: Veure
The RADMED project is devoted to the implementation and maintenance of a multidisciplinary monitoring system around the Spanish Mediterranean waters. This observing system is based on periodic multidisciplinary cruises covering the coastal waters, continental shelf and slope waters and some deep stations (> 2000 m) from the Westernmost Alboran Sea to Barcelona in the Catalan Sea, including the Balearic Islands. This project was launched in 2007 unifying and extending some previous monitoring projects which had a more reduced geo- graphical coverage. Some of the time series currently available extend from 1992, while the more recent ones were initiated in 2007. The present work updates the available time series up to 2015 (included) and shows the capability of these time series for two main purposes: the calculation of mean values for the properties of main water masses around the Spanish Mediterranean, and the study of the interannual and decadal variability of such properties. The data set provided by the RADMED project has been merged with historical data from the MEDAR/MEDATLAS data base for the calculation of temperature and salinity trends from 1900 to 2015. The analysis of these time series shows that the intermediate and deep layers of the Western Mediterranean have increased their temperature and salinity with an acceleration of the warming and salting trends from 1943. Trends for the heat absorbed by the water column for the 1943–2015 period, range between 0.2 and 0.6 W/m2 depending on the used methodology. The temperature and salinity trends for the same period and for the in- termediate layer are 0.002 °C/yr and 0.001 yr−1 respectively. Deep layers warmed and increased their salinity at a rate of 0.004 °C/yr and 0.001 yr−1.
Paraules clau: Western Mediterranean Monitoring program Warming and salting trends Climate change
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Yu K., Dong C., King G. (2017)
Journal of Geophysical Research: Oceans, 122, 4 DOI: 10.1002/ 2016JC012404. (BibTeX: yu.etal.2017)
Resum: Veure
We investigate mesoscale turbulence (10–1000 km) in the ocean winds over the Kuroshio Extension (28ºN–40ºN, 140ºE–180ºE) using the QuikSCAT data set (November 1999 to October 2009). We calculate the second (Djj) and third-order structure functions (Djjj) and the spatial variance (Vj) as a function of scale r (j5L; T denotes, respectively, the longitudinal (divergent) and transverse (vortical) component). The most interesting results of the analysis follow. Although both VjðrÞ and DjjðrÞ measure the turbulent kinetic energy (TKE), we find that VjðrÞ is the more robust measure. The spatial variance density (dVj/dr) has a broad peak near 450 km (close to the midlatitude Rossby radius of deformation). On interannual time scales, TKE correlates well with the El Ni~no 3.4 index. According to turbulence theory, the kinetic energy cascades downscale (upscale) if DLLLðrÞ (also skewness SL5DLLL=D3=2 LL ) is negative (positive). Our results for the Kuroshio Extension are consistent with a downscale cascade (indicating convergence dominates). Furthermore, classical turbulence theory predicts that SL520:3 and independent of r; however, we find SL varies strongly with r, from24 at small scales to 20.3 at large scales. This nonclassical behavior implies strong-scale interaction, which we attribute to the rapid, and sometimes explosive, growth of storms in the region through baroclinic instability. Finally, we find that ST (a measure of cyclonic/anticyclonic asymmetry) is positive (cyclonic) and also varies strongly with r, from 4 at small scales to 0.5 at large scales. New turbulence models are needed to explain these results, and that will benefit Weather Prediction and climate modeling.
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Bardaji R., Sánchez A.M., Simon C., Wernand M.R., Piera J. (2016)
Sensors, 16, 3 DOI: 10.3390/s16030373. (BibTeX: bardaji.etal.2016c)
Resum: Veure
A critical parameter to assess the environmental status of water bodies is the transparency of the water, as it is strongly affected by different water quality related components (such as the presence of phytoplankton, organic matter and sediment concentrations). One parameter to assess the water transparency is the diffuse attenuation coefficient. However, the number of subsurface irradiance measurements obtained with conventional instrumentation is relatively low, due to instrument costs and the logistic requirements to provide regular and autonomous observations. In recent years, the citizen science concept has increased the number of environmental observations, both in time and space. The recent technological advances in embedded systems and sensors also enable volunteers (citizens) to create their own devices (known as Do-It-Yourself or DIY technologies). In this paper, a DIY instrument to measure irradiance at different depths and automatically calculate the diffuse attenuation Kd coefficient is presented. The instrument, named KdUINO, is based on an encapsulated low-cost photonic sensor and Arduino (an open-hardware platform for the data acquisition). The whole instrument has been successfully operated and the data validated comparing the KdUINO measurements with the commercial instruments. Workshops have been organized with high school students to validate its feasibility.
Paraules clau: Arduino, buoy, citizen science, do-it-yourself, KdUINO, light, low-cost sensor, oceanography; diffuuse attenuation coefficient
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Busch J.A., Bardaji R., Ceccaroni L., Friedrichs A., Piera J., Simon C., Thijsse P., Wernand M., van der Woerd H.J., Zielinski O. (2016)
Remote Sensing, 8, 11, 879. DOI: 10.3390/rs8110879. (BibTeX: busch.etal.2016a)
Resum: Veure
Marine processes are observed with sensors from both the ground and space over large spatio-temporal scales. Citizen-based contributions can fill observational gaps and increase environmental stewardship amongst the public. For this purpose, tools and methods for citizen science need to (1) complement existing datasets; and (2) be affordable, while appealing to different user and developer groups. In this article, tools and methods developed in the 7th Framework Programme of European Union (EU FP 7) funded project Citclops (citizens’ observatories for coast and ocean optical monitoring) are reviewed. Tools range from a stand-alone smartphone app to devices with Arduino and 3-D printing, and hence are attractive to a diversity of users; from the general public to more specified maker- and open labware movements. Standardization to common water quality parameters and methods allows long-term storage in regular marine data repositories, such as SeaDataNet and EMODnet, thereby providing open data access. Due to the given intercomparability to existing remote sensing datasets, these tools are ready to complement the marine datapool. In the future, such combined satellite and citizen observations may set measurements by the engaged public in a larger context and hence increase their individual meaning. In a wider sense, a synoptic use can support research, management authorities, and societies at larg.
Paraules clau: citizen’s applications for earth surveillance, smartphones, open labware, interoperability, aquatic optics, incentives to mobilize the crowd, emerging technologies, data repositories, DIY, open access
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Camps A., Gabarró C., Vall-llossera M., Blanch S., Aguasca A., Torres F., Corbella I., Duffo N., Turiel A., Portabella M., Ballabrera-Poy J., González-Gambau V., Martínez J., Villarino R., Enrique L., Monerris A., Bosch X., Sabia R., Talone M., Piles M., Pablos M., Valencia E. (2016)
Scientia Marina, 80, S1, 159-172. DOI: 10.3989/scimar.04285.04A. (BibTeX: camps.etal.2016b)
Resum: Veure
This article summarizes some of the activities in which Jordi Font, research professor and head of the Department of Physical and Technological Oceanography, Institut de Ciències del Mar (CSIC, Spanish National Research Council) in Barcelona, has been involved as co-Principal Investigator for Ocean Salinity of the European Space Agency Soil Moisture and Ocean Salinity (SMOS) Earth Explorer Mission from the perspective of the Remote Sensing Lab at the Universitat Politècnica de Catalunya. We have probably left out some of his many contributions to salinity remote sensing, but we hope that this review will give an idea of the importance of his work. We focus on the following issues: 1) the new accurate measurements of the sea water dielectric constant, 2) the WISE and EuroSTARRS field experiments that helped to define the geophysical model function relating brightness temperature to sea state, 3) the FROG 2003 field experiment that helped to understand the emission of sea foam, 4) GNSS-R techniques for improving sea surface salinity retrieval, 5) instrument characterization campaigns, and 6) the operational implementation of the Processing Centre of Levels 3 and 4 at the SMOS Barcelona Expert Centre.
Paraules clau: SMOS, radiometry, interferometry, calibration, validation, salinity, soil moisture, sea ice, GNSS-R, radiometría, interferometría, calibración, validación, salinidad, humedad del terreno, hielo marino
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Chaparro D., Vall-llossera M., Piles M., Camps A., Rüdiger C., Riera-Tatché R. (2016)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 9, 6, 2818--2829. DOI: 10.1109/JSTARS.2016.2571838. (BibTeX: chaparro.etal.2016b)
Resum: Veure
Recent climate trends evidence a rise of temperatures and an increase in the duration and intensity of droughts which is in turn leading to the occurrence of larger wildfires, which threaten the environment as well as human lives and beings. In this context, improved wildfires prediction tools are urgently needed. In this paper, the use of remotely sensed soil moisture data as a key variable in the climate-wildfires relationship is explored. The study is centered in the fires registered in the Iberian Peninsula during the period 2010–2014. Their prior-to-occurrence surface moisturetemperature conditions were analyzed using SMOS-derived soil moisture data and ERA-Interim land surface temperature reanalysis. Results showed that moisture and temperature conditions limited the extent of wildfires, and a potential maximum burned area per moisture-temperature paired values was obtained (R2= 0.43). The model relating fire extent with moisture-temperature preconditions was improved by including information on land cover, regions, and the month of the fire outbreak (R2= 0.68). Model predictions had an accuracy of 83.3% with a maximum error of 40.5 ha. Results were majorly coherent with wildfires behavior in the Iberian Peninsula and reflected the duality between Euro-Siberian and Mediterranean regions in terms of expected burned area. The proposed model has a promising potential for the enhancement of fire prevention services.
Paraules clau: Wildfires, remote sensing, soil moisture measurements,land surface temperature, and burned area.
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Chaparro D., Vayreda J., Vall-llossera M., Banqué M., Piles M., Camps A., Martínez-Vilalta J. (2016)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 99, 1--12. DOI: 10.1109/JSTARS.2016.2585505. (BibTeX: chaparro.etal.2016c)
Resum: Veure
Increased intensity and duration of droughts and high temperature events have been associated with forest decline in many parts of the world, and these decline events are expected to become more common under climate change. There is therefore a need for monitoring and modelling of forest decline. We used a regional forest condition monitoring program (DEBOSCAT) to study the spatial distribution of decline events in 2012 in Catalonia (Northeastern Spain) and their relationship with climatic factors. In 2012, this dataset was collected after an extraordinarily dry summer, and allowed the study of decline events in eight dominant tree species. We fitted a logistic model to predict forest decline probability as a function of species, precipitation and temperature anomalies, solar radiation, and remotely sensed soil moisture data from the Soil Moisture and Ocean Salinity (SMOS) mission. Broadleaved species were more affected by decline events than conifers. The statistical model explained almost 40% of forest decline occurrence, wherein almost 50% of this variability was explained by species effect, with broadleaved trees being generally more sensitive to the studied factors than conifers. Climatically wetter areas and those more exposed to radiation were more likely to be affected, suggesting better adaptation of forests in dry areas. In general, more damaged forests were characterized by high positive temperature anomalies, lower than average rainfall, and low soil moisture in summer 2012. The most vulnerable species was Fagus sylvatica, a Euro-Siberian species, contrasting with Pinus halepensis, a typically Mediterranean species, which showed low sensitivity to drought.
Paraules clau: Forest decline; Drought; Temperature anomalies; SMOS; Soil moisture; Regional scale; Predictive modelling; Forest monitoring; Climate change
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Emelianov M., Cruzado A., Olivar M.P., Lleonart J. (2016)
Scientia Marina, 80S1, 25-29. (BibTeX: emelianov.etal.2016a)
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García-Ladona E., Salvador J., Fernández P., Pelegrí J.L., Elósegui P., Sánchez O., Jiménez J.A., Pérez F., Ballabrera J., Isern-Fontanet J., Salat J., Font J. (2016)
Scientia Marina, 80S1, 141-158. DOI: 10.3989/scimar.04325.14A. (BibTeX: garcialadona.etal.2016d)
Resum: Veure
Since the mid-1980s, physical oceanographers at the Institute of Marine Sciences have been involved in the use of Lagrangian drifters as a complementary technology for their oceanographic research. As Lagrangian observations became more feasible, these researchers continued developing their own drifters in what was to be the seed of current technological activities at the Physical and Technological Oceanography Department. In this paper we overview the work done during the last 30 years with special focus on Lagrangian developments from the initial activities to the latest developments. In addition to basic oceanography research applications, Lagrangian technological developments include prototypes for measuring surface and subsurface ocean properties, for tracking purposes in search and rescue operations and pollution events, and for monitoring ice motion and thickness in the Arctic. The paper emphasizes original and unpublished technical aspects related to the latest developments.
Paraules clau: Lagrangian drifters; sea surface measurements; salinity measurements; oil spills drifters; SMOS.
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Garcia-Olivares A. (2016)
Scientia Marina, 80S1, 257-268. DOI: 10.3989/scimar.04295.12A. (BibTeX: garciaolivares.2016a)
Resum: Veure
A feasible way to avoid the risk of energy decline and to combat climate change is to build a worldwide, 100% renewable energy mix. Renewable energy can be scaled up to the range of 12 electric terawatts (TWe) if 10% of continental shelves are exploited with floating turbines to depths as low as 225 m, 5% of continents with ground turbines, and 5% of the main deserts with concentrating solar power (CSP) farms. However, a globally electrified economy cannot grow much above 12 TWe without approaching the limit of terrestrial copper reserves. New photovoltaic silicon panels do not use silver metallization pastes and could contribute up to 1 TW of decentralized residential power. Hydroelectricity has a potential of 1 TW but a fraction of this would have to be sacrificed for energy storage purposes. Hydro, CSP, wave energy and grid integration at continental scales may be sufficient to fit supply to demand, avoiding intermittency. The renewable energy mix would have an energy return on energy invested about 18, which is 25% lower than the estimated present one. That should be sufficient to sustain an industrialized economy provided that the substitution of electricity for fossil fuels is done intelligently.
Paraules clau: 100% renewable energy; renewable potential; EROEI; material limits; post-carbon economy
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González-Gambau V., Turiel A., Olmedo E., Martínez J., Corbella I., Camps A. (2016)
IEEE Transactions on Geoscience and Remote Sensing, 54, 4, 2314-2328. DOI: 10.1109/TGRS.2015.2499324. (BibTeX: gonzalezgambau.etal.2016a)
Resum: Veure
Soil moisture and ocean salinity (SMOS) brightness temperature (TB) images and calibrated visibilities are related by the so-called G-matrix. Due to the incomplete sampling at some spatial frequencies, sharp transitions in the TB scenes generate a Gibbs-like contamination ringing and spread sidelobes. In the current SMOS image reconstruction strategy, a Blackman window is applied to the Fourier components of the TBs to diminish the amplitude of artifacts such as ripples, as well as other Gibbs-like effects. In this paper, a novel image reconstruction algorithm focused on the reduction of Gibbs-like contamination in TB images is proposed. It is based on sampling the TB images at the nodal points, that is, at those points at which the oscillating interference causes the minimum distortion to the geophysical signal.Results show a significant reduction of ripples and sidelobes in strongly radio-frequency interference contaminated images. This technique has been thoroughly validated using snapshots over the ocean, by comparing TBs reconstructed in the standard way or using the nodal sampling (NS) with modeled TBs. Tests have revealed that the standard deviation of the difference between the measurement and the model is reduced around 1 K over clean and stable zones when using NS technique with respect to the SMOS image reconstruction baseline. The reduction is approximately 0.7 K when considering the global ocean. This represents a crucial improvement in TB quality, which will translate in an enhancement of the retrieved geophysical parameters, particularly the sea surface salinity
Paraules clau: Image reconstruction, interferometric radiometer, nodal points, nodal sampling (NS), radio-frequency interferences (RFIs), sidelobes, soil moisture and ocean salinity (SMOS).
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González-Gambau V., Olmedo E., Turiel A., Martínez J., Ballabrera J., Portabella M., Piles M. (2016)
Remote Sensing of Environment, 180, 205-220. DOI: 10.1016/j.rse.2015.12.032. (BibTeX: gonzalezgambau.etal.2016f)
Resum: Veure
Abrupt changes in the SoilMoisture and Ocean Salinity (SMOS) brightness temperatures, such as those produced by land/sea/ice transitions and Radio-Frequency Interference (RFI) sources, produce artificial rippling patterns (i.e. the so-called Gibbs-like contamination) that propagate through the SMOS-reconstructed image. A nodal sampling technique, focused on the reduction of this kind of contamination by sampling at the points where the perturbation cancels,was introduced by González-Gambau et al. (2015). In thisworkwe showthat the quality of nodal sampling can be largely improved by refining the determination of the nodal grid. In addition, we have carried out an extensive validation of the resulting data over the ocean. Nodal sampling reduces sidelobe levels and ripples in the reconstructed images leading to brightness temperatures in better agreement with the the oretically modeled ones. Validation of the salinity retrievals against close-to-surface Argo salinity observations shows that nodal sampling leads to improved salinity retrievals in open ocean,while close to the coast land–sea contamination seems to deteriorate the quality. Besides, spectral analysis shows that nodal sampled salinities become closer to what is geophysically expected without loss of effective spatial resolution.
Paraules clau: Soil Moisture and Ocean Salinity (SMOS) Interferometry Radiometry Image reconstruction Nodal sampling Nodal points Sidelobes Radio Frequency Interferences (RFI) Salinity retrievals
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González-Zamora Á., Sánchez N., Martínez-Fernández J., Gumuzzio A., Piles M., Olmedo E. (2016)
Physics and Chemistry of the Earth, Parts A/B/C, 83-84, 123-136. DOI: http://dx.doi.org/10.1016/j.pce.2015.05.009. (BibTeX: gonzalezzamora.etal.2016)
Resum: Veure
The European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) Level 2 soil moisture and the new L3 product from the Barcelona Expert Center (BEC) were validated from January 2010 to June 2014 using two in situ networks in Spain. The first network is the Soil Moisture Measurement Stations Network of the University of Salamanca (REMEDHUS), which has been extensively used for validating remotely sensed observations of soil moisture. REMEDHUS can be considered a small-scale network that covers a 1300 km2 region. The second network is a large-scale network that covers the main part of the Duero Basin (65,000 km2). At an existing meteorological network in the Castilla y Leon region (Inforiego), soil moisture probes were installed in 2012 to provide data until 2014. Comparisons of the temporal series using different strategies (total average, land use, and soil type) as well as using the collocated data at each location were performed. Additionally, spatial correlations on each date were computed for specific days. Finally, an improved version of the Triple Collocation (TC) method, i.e., the Extended Triple Collocation (ETC), was used to compare satellite and in situ soil moisture estimates with outputs of the Soil Water Balance Model Green-Ampt (SWBM-GA). The results of this work showed that SMOS estimates were consistent with in situ measurements in the time series comparisons, with Pearson correlation coefficients (R) and an Agreement Index (AI) higher than 0.8 for the total average and the land-use averages and higher than 0.85 for the soil-texture averages. The results obtained at the Inforiego network showed slightly better results than REMEDHUS, which may be related to the larger scale of the former network. Moreover, the best results were obtained when all networks were jointly considered. In contrast, the spatial matching produced worse results for all the cases studied. These results showed that the recent reprocessing of the L2 products (v5.51) improved the accuracy of soil moisture retrievals such that they are now suitable for developing new L3 products, such as the presented in this work. Additionally, the validation based on comparisons between dense/sparse networks and satellite retrievals at a coarse resolution showed that temporal patterns in the soil moisture are better reproduced than spatial patterns.
Paraules clau: SMOS; Soil moisture; Validation; Extended Triple Collocation; Hydrological modeling
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Grieco G., Lin W., Migliaccio M., Nirchio F., Portabella M. (2016)
International Journal of Remote Sensing, 37, 21, 5086-5104. DOI: 10.1080/01431161.2016.1226525. (BibTeX: grieco.etal.2016d)
Resum: Veure
Sea wind and sea state estimation by synthetic aperture radar (SAR) measurements is a topic of relevance both on the scientific and user side. The new European Space Agency (ESA) Sentinel-1 constellation is meant to support marine studies and ensure highquality data. In this paper, we investigate the azimuth cut-off (λC) sea wind speed and significant wave height retrieval approach by taking benefit of two sets of multi-look SAR images with incidence angles varying from 20° to 45°. The images have been co-located with sea surface wind measurements acquired by the scatterometer onboard the Chinese satellite HY-2A (HSCAT) and with the European Centre for Medium Range Weather Forecast (ECMWF) operational model output. This study is meant to analyse both the empirical dependency of SAR λC on significant wave height (Hs) and wind speed (U). Several fitting geophysical model functions (λC-GMFs) are proposed and discussed. The results show that λC is strongly correlated with the significant wave height in all sea state conditions, while the correlation with the wind speed is only high for fully developed sea states. The azimuth cut-off based significant wave height retrievals are compared with independent National Data Buoy Centre (NDBC) network observations, showing a root mean square difference of about 0.5 m.
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Grifoll M., Aretxabaleta A.L., Pelegrí J.L., Espino M. (2016)
Ocean Science, 12, 1, 137-151. DOI: 10.5194/os-12-137-2016. (BibTeX: grifoll.etal.2016a)
Resum: Veure
We investigate the rapidly changing equilibrium between the momentum sources and sinks during the passage of a single two-peak storm over the Catalan inner shelf (NW Mediterranean Sea). Velocity measurements at 24 m water depth are taken as representative of the inner shelf, and the cross-shelf variability is explored with measurements at 50 m water depth. During both wind pulses, the flow accelerated at 24 m until shortly after the wind maxima, when the bottom stress was able to compensate for the wind stress. Concurrently, the sea level also responded, with the pressure-gradient force opposing the wind stress. Before, during and after the second wind pulse, there were velocity fluctuations with both super- and sub-inertial periods likely associated with transient coastal waves. Throughout the storm, the Coriolis force and wave radiation stresses were relatively unimportant in the along-shelf momentum balance. The frictional adjustment timescale was around 10 h, consistent with the e-folding time obtained from bottom drag parameterizations. The momentum evolution at 50 m showed a larger influence of the Coriolis force at the expense of a decreased frictional relevance, typical in the transition from the inner to the mid-shelf.
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Isern-Fontanet J., Olmedo E., Turiel A., García-Ladona E. (2016)
Geophysical Research Letters DOI: 10.1002/2016GL069595. (BibTeX: isernfontanet.etal.2016a)
Resum: Veure
The circulation in the Algerian Basin is characterized by the presence of fresh-core eddies that propagate along the coast or at distances between 100 and 200 km from the coast. Enhancements in the processing of the Soil Moisture and Ocean Salinity (SMOS) data have allowed to produce, for the first time, satellite sea surface salinity (SSS) maps in the Mediterranean Sea that capture the signature of Algerian eddies. SMOS data can be used to track them for long periods of time, especially during winter. SMOS SSS maps are well correlated with in situ measurements although the former has a smaller dynamical range. Despite this limitation, SMOS SSS maps capture the key dynamics of Algerian eddies allowing to retrieve velocities from SSS with the correct sign of vorticity.
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Lang S., Lin W., Bao Q., Zhang Y. (2016)
Remote Sensing Technology and Application, 31, 6, 1069-1074. DOI: 10.11873/j.issn.1004-0323.2016.6.1069. (BibTeX: lang.etal.2016a)
Resum: Veure
Wave numerical simulations of East China Sea,Eastern Pacific and central Pacific waters near Hawaii are carried out based on third-generation wave model WAVEWATCH Ⅲ,using NCEP/QuikSCAT wind field as model mixed input.In East China Sea,it is obtained that significant wave height and the reference value of buoy has a strong correlation coefficient,and the root mean square error of wave height is about 0.5 m by simulation;In the Pacific waters near the east coast and Hawaii,significant wave height values are generally lower than the reference value of buoy,root mean square error of wave height of different months is between 0.4 and 1.2 m,but the simulation of wave height and the reference value of buoy still has strong correlation.The results show that it is feasible that taking advantage of WAVEWATCH Ⅲ combined NCEP/QuikSCAT mixed wind field to simulate the wave height of East China Sea.However,it is still necessary to consider some non-wind factors in simulation of wave height lies at Pacific Ocean and the eastern open deep waters.
Paraules clau: WAVEWATCH Ⅲ NCEP/QuikSCAT mixed wind field Significant wave height Buoy
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Lin W., Portabella M., Turiel A., Stoffelen A., Verhoef A. (2016)
IEEE Transactions on Geoscience and Remote Sensing, 54, 7, 3890-3898. DOI: 10.1109/TGRS.2016.2529700. (BibTeX: lin.etal.2016l)
Resum: Veure
Singularity analysis has proven to be a complementary tool to the Advanced Scatterometer (ASCAT) inversion residual (or maximum likelihood estimator) in terms of wind quality control (QC). In this paper, a new implementation scheme of singularity exponent (SE) is developed for ASCAT data analysis. It combines the wavelet projections of the gradient measurements of multiple parameters into the analysis, ensuring that the analyzed parameters contribute equally to the final singularity map. Therefore, the underlying geophysical phenomena in the different ASCAT-derived parameters can be effectively revealed simultaneously on a unique map of SEs. The validation using both buoy winds and European Centre for Medium-Range Weather Forecasting forecast wind output shows that the newly derived SE significantly improves the current ASCAT wind QC. In particular, poor-quality ASCAT measurements at low-wind and high-variability conditions (w < 4 text{m/s}) can be effectively screened using the new SE.
Paraules clau: Advanced Scatterometer (ASCAT), maximum likelihood estimator (MLE), quality control (QC), singularity vanalysis (SA), wind variability
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Lin W., Portabella M., Stoffelen A., Vogelzang J., Verhoef A. (2016)
Quarterly Journal of the Royal Meteorological Society, 142, 697, 1745-1756. DOI: 10.1002/qj.2770. (BibTeX: lin.etal.2016m)
Resum: Veure
The two-dimensional variational ambiguity removal (2DVAR) method provides a spatial analysis of the sampled ocean vector winds to resolve the local Advanced Scatterometer (ASCAT) dual wind vector ambiguity. Like other variational meteorological data assimilation systems in numerical weather prediction (NWP), 2DVAR combines ASCAT observations with prior NWP background information, in this case from the European Centre for Medium-range Weather Forecasts (ECMWF). Although 2DVAR is generally effective, it may select the wrong ambiguity under certain conditions, e.g. when the background mislocates frontal areas or low-pressure centres, or when it misses convective systems. The relative influence of the ASCAT and ECMWF wind fields in the resulting 2DVAR analysis field can be controlled by adjusting the background error spatial correlation structure, and the background and/or observation error variances. In this article an adaptive 2DVAR approach is proposed to improve ASCAT ambiguity removal, using background error spatial correlations estimated from the autocorrelation of observed scatterometer wind components minus ECMWF forecasts, and using observation and background errors estimated from triple collocation analysis on collocated buoy, ASCAT and ECMWF data. The triple collocations are segregated into several categories according to the ASCAT-derived parameters that have proven to be effective in detecting the correct position of frontal lines and low-pressure centres. Verification using a typical cyclone case and collocated ASCAT and buoy winds shows that the 2DVAR analysis as well as the ASCAT ambiguity removal is improved significantly by putting more weight on the ASCAT observations using empirically determined spatial background error structure functions and situation-dependent observation/background error variances.
Paraules clau: scatterometer;data assimilation;ambiguity removal;mesoscale;singularity analysis
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Machín F.J., Pelegrí J.L. (2016)
Scientia Marina, 80S1, 205-214. DOI: 10.3989/scimar.04289.06A. (BibTeX: machin.pelegri.2016b)
Resum: Veure
Mediterranean Water lenses (meddies) in the eastern North Atlantic, north of the Canary Islands, appear to often have their salty and nutrient-poor core accompanied by relatively fresh and nutrient-rich waters on top. We describe several occurrences of freshwater halos and berets for meddies sampled north of the Canary Islands—with instrumented moorings, Argo floats and oceanographic cruises—and identify the source of these fresh anomalies as diluted Antarctic Intermediate Water (AAIW). We propose that this capping takes place off Northwest Africa, as the southward-advected meddy interacts with the northward-advected AAIW. This interpretation is consistent with a simple analysis of the relevant advective-diffusive time scales associated with the passage of meddies under a layer of AAIW, and suggests that meddies may be a mechanism for AAIW export far into the North Atlantic Ocean.
Paraules clau: meddies; Antarctic Intermediate Water; eastern North Atlantic.
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Martinez J., Turiel A., González-Gambau V., Olmedo E. (2016)
IEEE Transactions on Geoscience and Remote Sensing, 54, 8, 4906-4910. DOI: 10.1109/TGRS.2016.2552647. (BibTeX: martinez.etal.2016b)
Resum: Veure
Since its launch in 2009, the European Space Agency mission Soil Moisture and Ocean Salinity (SMOS) has provided valuable information on soil moisture, sea surface salinity data, and other geophysical variables. Due to its innovative instrument, an L-band 2-D synthetic aperture interferometric radiometer, SMOS is able to provide high-resolution L2 data (as compared with other L-band missions). However, SMOS processing is complex, giving rise to the emergence of some unexpected biases. In this paper, we have analyzed the spatial structure of two-point correlations owing to the SMOS synthetic antenna, finding that they are not negligible. Those correlations can be characterized by means of effective point spread functions (PSFs). This paper indicates that theSMOS PSFmatrix can be computed in a fast way from measured data without the need for any model or auxiliary data. Furthermore, this matrix can be described in terms of a convolution kernel. The knowledge of that convolution kernel can be used to improve the quality of theSMOS image and to assess the effect of changes of processing procedures, including calibration methods.
Paraules clau: Imaging, point spread functions (PSFs), radiometry, remote sensing, signal processing, Soil Moisture and Ocean Salinity (SMOS).
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Martín-Neira M., Oliva R., Corbella I., Torres F., Duffo N., Durán I., Kainulainen J., Closa J., Zurita A., Cabot F., Khazaal A., Anterrieu E., Barbosa J., Lopes G., Tenerelli J., Díez-García R., Fauste J., Martín-Porqueras F., González-Gambau V., Turiel A., Delwart S., Crapolicchio R., Suess M. (2016)
Remote Sensing of Environment, 180, 19-39. DOI: 10.1016/j.rse.2016.02.036. (BibTeX: martinneira.etal.2016b)
Resum: Veure
ESA's Soil Moisture and Ocean Salinity (SMOS) mission, launched 2-Nov-2009, has been in orbit for over 6 years, and its Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) in two dimensions keeps working well. The calibration strategy remains overall as established after the commissioning phase, with a few improvements. The data for this whole period has been reprocessed with a new fully polarimetric version of the Level-1 processor which includes a refined calibration schema for the antenna losses. This reprocessing has allowed the assessment of an improved performance benchmark. An overview of the results and the progress achieved in both calibration and image reconstruction is presented in this contribution.
Paraules clau: Soil Moisture and Ocean Salinity (SMOS)Mission, Soil moisture, Sea surface salinity, L-Band radiometry, Aperture synthesis, MIRAS
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Mecklenburg S., Drusch M., Kaleschke L., Rodriguez-Fernandez N., Reul N., Kerr Y., Font J., Martin-Neira M., Oliva R., Daganzo-Eusebio E., Grant J.P., Sabia R., Macelloni G., Rautiainen K., Fauste J., de Rosnay P., Munoz-Sabater J., Verhoest N., Lievens H., Delwart S., Crapolicchio R., de la Fuente A., Kornberg M. (2016)
Remote Sensing of Environment, 180, 3-18. DOI: 10.1016/j.rse.2015.12.025. (BibTeX: mecklenburg.etal.2016c)
Resum: Veure
The Soil Moisture and Ocean Salinity (SMOS) mission, launched in November 2009, is the European Space Agency\'s (ESA) second Earth Explorer Opportunity mission. The scientific objectives of the SMOS mission directly respond to the need for global observations of soil moisture and ocean salinity, two key variables used in predictive hydrological, oceanographic and atmospheric models. SMOS observations also provide information on vegetation, in particular plant available water and water content in a canopy, drought index and flood risks, surface ocean winds in storms, freeze/thaw state and sea ice and its effect on ocean-atmosphere heat fluxes and dynamics affecting large-scale processes of the Earth\'s climate system. Significant progress has been made over the course of the now 6-year life time of the SMOS mission in improving the ESA provided level 1 brightness temperature and level 2 soil moisture and sea surface salinity data products. The main emphasis of this paper is to review the status of the mission and provide an overview and performance assessment of SMOS data products, in particular with a view towards operational applications, and using SMOS products in data assimilation. SMOS is in excellent technical condition with no limiting factors for operations beyond 2017. The instrument performance fulfils the requirements. The radio-frequency interference (RFI) contamination originates from man-made emitters on ground, operating in the protected L-band and adding signal to the natural radiation emitted by the Earth. RFI has been detected worldwide and has been significantly reduced in Europe and the Americas but remains a constraint in Asia and the Middle East. The mission\'s scientific objectives have been reached over land and are approaching the mission objectives over ocean. This review paper aims to provide an introduction and synthesis to the papers published in this RSE special issue on SMOS
Paraules clau: Soil Moisture and Ocean Salinity (SMOS) mission, Sea surface salinity, Soil moisture, Sea ice thickness, Vegetation optical depth, Severe wind tracking, Data assimilation, Hydrological forecasting, L-band radiometry, Satellite remote sensing, Freeze and thaw
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Olivar M.P., González-Gordillo J.I., Salat J., Chust G., Cózar A., Hernández-León S., Fernández de Puelles M.L., Irigoien X. (2016)
Marine and Freshwater Research, 67, 8, 1114-1127. DOI: 10.1071/MF14391. (BibTeX: olivar.etal.2016)
Resum: Veure
Surface waters are an attractive foraging ground for small fish in the open ocean. This study aims to determine the importance of vertically migrating species in the neuston of oceanic waters across the Atlantic, Indian and Pacific Oceans and to ascertain the influence of environmental variables on their distribution patterns. Neustonic fish assemblages were primarily controlled by light. They were dominated by late-larvae and juveniles of Exocoetidae, Hemiramphidae and Scomberesocidae during the day. At night, the vertical migration of mesopelagic species changed the dominance pattern in favour of Myctophidae and Scomberesocidae. The neustonic families’ distribution was primarily related to sea surface temperatures, whereas environmental variables at deeper layers were related to mesopelagic migrating families. Canonical correspondence analysis showed a low but statistically significant contribution of several environmental variables to myctophid species composition (10%), with minimum oxygen concentrations ranking first in variance explanation followed by maximum fluorescence, sea surface temperature and 400-m temperature. Spatial autocorrelation also explained 17% of the variance, indicating the influence of other factors such as historical, demographic and dispersal constraints. The low number of myctophid species in the North Pacific Equatorial Countercurrent appears to be related to the low oxygen concentrations observed in this province.
Paraules clau: Ichthyoneuston, ichthyoplankton, micronekton, Myctophidae, oceanic realm, pelagic biogeography, vertical migration
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Olivar M.P., Sabatés A., Pastor M.V., Pelegrí J.L. (2016)
Deep-Sea Research. Part I: Oceanographic Research Papers, 117, 120-137. DOI: 10.1016/j.dsr.2016.10.003. (BibTeX: olivar.etal.2016b)
Resum: Veure
We explore the associations between larval fish assemblages and oceanographic conditions in the upper ocean (top 200 m) along the African slope, from tropical (15°N) to subtropical (35°N) latitudes, during a period of intense upwelling. In this extensive region, the northward Mauritanian Current and Poleward Undercurrent carry South Atlantic Central Waters (SACW) while the southward Canary Upwelling Current transports North Atlantic Central Waters (NACW). South of Cape Blanc we only find SACW, and north of Cape Blanc there is NACW far offshore and a combination of NACW and SACW nearshore, separated by the Canary Upwelling Front (CUF). The larvae of different myctophid species serve as indicators of the water masses, e.g. S. veranyi and M. punctatum were found in some coastal stations that were dominated by NACW, while the tropical mesopelagic B. argyrogaster, H. macrochir, M. affine and S. kreffti were associated to the SACW. The along-slope offshore convergence of NACW and SACW takes place at the Cape Verde Frontal Zone (CVFZ), representing a region of extensive offshore export for larvae of coastal species, S. pilchardus and E. encrasicolus, far from their nearshore spawning area. The large-scale frontal systems (CVFZ and CUF) and mesoscale eddies contribute to retain larvae within productive waters, influencing both coastal and oceanic species.
Paraules clau: Fish larvae, mesoscale hydrography, Canary upwelling, Cape Verde Frontal Zone, mesoscale eddies
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Olmedo E., Martínez J., Umbert M., Hoareau N., Portabella M., Ballabrera J., Turiel A. (2016)
Remote Sensing of Environment, 180, 246-263. DOI: 10.1016/j.rse.2016.02.038. (BibTeX: olmedo.etal.2016e)
Resum: Veure
The multifractal fusion is a non-parametric technique that merges remotely-sensed maps of different ocean variables to produce higher quality remote sensing products. This method was first introduced to reduce the noise level in a map of a given ocean variable provided that a higher-quality map of a second ocean variable is available. In this work, we go one step further in both the the oretical justification and the application of the multifractal fusion. In the first part of the paper we explore if the quality of the derived maps can be improved by using a higher-dimensional tensor relating the gradient of one variable with that of the other. Higherdimension tensors require the introduction of appropriate integration schemes to avoid inducing long-range artifacts, something that is not completely solved yet. The results show that although higher-dimension tensors lead to an improvement in the spatial consistency of the derived maps (i.e., a higher quality of the associated singularity exponents), the comparisonwith in situ data still showsignificant reconstruction errors as compared to the simplified scalar approach. In the second part of the paperwe have used the scalar approach to increase the spatial and temporal resolution of the current SoilMoisture and Ocean Salinity (SMOS) Level 3 sea surface salinity (SSS)maps produced at the Barcelona Expert Center (BEC). As such, new daily SMOS SSS globalmaps are generated at a 0.05°×0.05° grid resolution. The quality of the resulting products has been assessed using in-situ comparison, singularity analysis and power density spectra. It is concluded that the multifractal fusion can be used to significantly increase the spatial and temporal resolution of the SSS maps.
Paraules clau: Remote sensing Data fusion Data merging Physical oceanography Singularity analysis Multifractal SMOS SSS
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Pablos M., Martínez-Fernández J., Piles M., Sánchez N., Vall-llossera M., Camps A. (2016)
Remote Sensing, 8, 587. DOI: 10.3390/rs8070587. (BibTeX: pablos.etal.2016a)
Resum: Veure
Soil moisture (SM) is an important component of the Earth’s surface water balance and by extension the energy balance, regulating the land surface temperature (LST) and evapotranspiration (ET). Nowadays, there are two missions dedicated to monitoring the Earth’s surface SM using L-band radiometers: ESA’s Soil Moisture and Ocean Salinity (SMOS) and NASA’s Soil Moisture Active Passive (SMAP). LST is remotely sensed using thermal infrared (TIR) sensors on-board satellites, such as NASA’s Terra/Aqua MODIS or ESA & EUMETSAT’s MSG SEVIRI. This study provides an assessment of SM and LST dynamics at daily and seasonal scales, using 4 years (2011–2014) of in situ and satellite observations over the central part of the river Duero basin in Spain. Specifically, the agreement of instantaneous SM with a variety of LST-derived parameters is analyzed to better understand the fundamental link of the SM–LST relationship through ET and thermal inertia. Ground-based SM and LST measurements from the REMEDHUS network are compared to SMOS SM and MODIS LST spaceborne observations. ET is obtained from the HidroMORE regional hydrological model. At the daily scale, a strong anticorrelation is observed between in situ SM and maximum LST (R between -0.6 to -0.8), and between SMOS SM and MODIS LST Terra/Aqua day (R close to- 0.7). At the seasonal scale, results show a stronger anticorrelation in autumn, spring and summer (in situ R between -0.5 to -0.7; satellite R between -0.4 to -0.7) indicating SM–LST coupling, than in winter (in situ R close to +0.3; satellite R close to -0.3) indicating SM–LST decoupling. These different behaviors evidence changes from water-limited to energy-limited moisture flux across seasons, which are confirmed by the observed ET evolution. In water-limited periods, SM is extracted from the soil through ET until critical SM is reached. A method to estimate the soil critical SM is proposed. For REMEDHUS, the critical SM is estimated to be close to 0.12m3/m3, stable over the study period and consistent between in situ and satellite observations. A better understanding of the SM–LST link could not only help improving the representation of LST in current hydrological and climate prediction models, but also refining SM retrieval or microwave-optical disaggregation algorithms, related to ET and vegetation status.
Paraules clau: evapotranspiration; correlation; water-limited; energy-limited; coupling; disaggregation; critical soil moisture; REMEDHUS; SMOS; MODIS
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Pascual M., Neubert M.G., Acuña J.L., Solow A.R., Domínguez-Carrió C., Salvador J., Olariaga A., Fuentes V. (2016)
Marine Ecology Progress Series, 561, 189-201. DOI: 10.3354/meps11915. (BibTeX: pascual.etal.2016c)
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Pelegrí J.L. (2016)
Scientia Marina, 80, 4, 567-568. DOI: 10.3989/scimar.04570.20A. (BibTeX: pelegri.2016a)
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Pelegrí J.L., Gabarró C., Camps A. (2016)
Scientia Marina, 80S1, 15-24. (BibTeX: pelegri.etal.2016c)
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Pelegrí J.L., Vaqué D. (2016)
Scientia Marina, 80S1, 9-10. (BibTeX: pelegri.vaque.2016)
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Piles M., Petropoulos G., Sánchez N., González-Zamora A., Ireland G. (2016)
Remote Sensing of Environment, 180, 403-417. DOI: 10.1016/j.rse.2016.02.048. (BibTeX: piles.etal.2016a)
Resum: Veure
Earth Observation (EO) technology is today at a maturity level that allows deriving operational estimates of Surface Soil Moisture (SSM) from a variety of sensors; yet, such products are provided at present at a coarse spatial and/or temporal resolution, which restricts their use in local or regional scale studies and practical applications. Herein, a methodology to derive SSMestimates fromspace at previously unattained spatio-temporal resolutions is proposed. The method is based on a variant of the “triangle” inversion technique leveraging on the strengths and synergies ofSMOS (SoilMoisture and Ocean Salinitymission)microwave observations and geostationary optical/infrared data. The SSMretrieval technique allows for: i) enhancing the spatial resolution of SMOS SSMproductestimates to 3 km spatial resolution, and, ii) providing a temporal average daytime SM product from the instantaneous fine-scale SSMestimates acquired every 15min; the latter is allowing higher coverage in presence of clouds and representativeness (up to 96 estimates per day) in comparison to the instantaneous estimate at the time of satellite overpass.The proposed technique has been implemented to SMOS andMSG (Meteosat Second Generation) SEVIRI (Spinning Enhanced Visible and Infrared Imager) observations acquired over the Iberian Peninsula and Southern France during year 2011. SSM instantaneous estimates at the time of SMOS overpass and daytime-averaged SSM estimates have been obtained and evaluated separately against collocated in-situ measurements acquired froma total of 40 stations belonging to the REMEDHUS, VAS and SMOSMANIA permanent soilmoisturemeasurement networks. Statistical agreement between compared datasets has been evaluated both at individual stations and considering the network average on the basis of several statistical terms computed including correlation,bias, root-mean-squared errors, slope and intercept of linear regression. Results showed that the proposed method not only preserves the quality of SMOS SSMat finer spatial scales, but also allows achieving higher temporal coverage and representativeness in daytime averages. The synergy of SMOS and SEVIRI provides a pathway to enhance water cycle EO capabilities taking full advantage of the new observational records of SSM and operational geostationary information.
Paraules clau: Soil moisture SMOS MSG SEVIRI Synergy Downscaling Temporal resolution Spatial resolution
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Sánchez A.M., Piera J. (2016)
Biogeosciences, 13, 4081-4098. DOI: 10.5194/bg-13-4081-2016. (BibTeX: sanchez.piera.2016b)
Resum: Veure
The scattering properties of aquatic suspended particles have many optical applications. Several data inversion methods have been proposed to estimate important features of particles, such as their size distribution or their refractive index. Most of the proposed methods are based on the Lorenz–Mie theory to solve Maxwell\'s equations, where particles are considered homogeneous spheres. A generalization that allows consideration of more complex-shaped particles is the T-matrix method. Although this approach imposes some geometrical restrictions (particles must be rotationally symmetrical) it is applicable to many life forms of phytoplankton. In this paper, three different scenarios are considered in order to compare the performance of several inversion methods for retrieving refractive indices. The error associated with each method is discussed and analyzed. The results suggest that inverse methods using the T-matrix approach are useful to accurately retrieve the refractive indices of particles with complex shapes, such as for many phytoplankton organisms.
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Sánchez N., González-Zamora A., Piles M., Martínez-Fernández J. (2016)
Remote Sensing, 8, 4, 287. DOI: 10.3390/rs8040287. (BibTeX: sanchez.etal.2016b)
Resum: Veure
A new index for agricultural drought monitoring is presented based on the integration of different soil/vegetation remote sensing observations. The synergistic fusion of the surface soil moisture (SSM) from the Soil Moisture and Ocean Salinity (SMOS) mission, with the Moderate Resolution Imaging Spectroradiometer (MODIS) derived land surface temperature (LST), and water/vegetation indices for agricultural drought monitoring was tested. The rationale of the approach is based on the inverse relationship between LST, vegetation condition and soil moisture content. Thus, the proposed Soil Moisture Agricultural Drought Index (SMADI) combines the soil and temperature conditions while including the lagged response of vegetation. SMADI was retrieved every eight days at 500 m spatial resolution for the whole Iberian Peninsula (IP) from 2010 to 2014, and a time lag of eight days was used to account for the plant response to the varying soil/climatic conditions. The results of SMADI compared well with other agricultural indices in a semiarid area in the Duero basin, in Spain, and also with a climatic index in areas of the Iberian Peninsula under contrasted climatic conditions. Based on a standard classification of drought severity, the proposed index allowed for a coherent description of the drought conditions of the IP during the study period.
Paraules clau: drought; MODIS; SMOS; LST; NDVI; soil moisture; agriculture
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Solé J., Ballabrera-Poy J., Macías D., Catalán I.A. (2016)
Scientia Marina, 80S1, 249-256. DOI: http://dx.doi.org/10.3989/scimar.04290.04A. (BibTeX: sole.etal.2016g)
Resum: Veure
In this work we focus on the Alboran Sea (western Mediterranean) to relate wind field and ocean velocity variability with chlorophyll a (Chl a) behaviour, using a 2-km resolution, coupled 3D ocean circulation-NPZD model (ROMS). The analysis is done in three steps. First, we split the seasonal and residual contribution for the fields under study. Second, we calculate the corresponding empirical orthogonal functions (EOFs) for the seasonal and residual parts. Finally, we relate each pair of variables for both seasonal and residual contribution EOFs. The results reported here allow the links between wind and Chl a to be quantified. We explain these links in terms of the ocean velocity field acting as a driver of Chl a variability. The results show that, although the seasonal part of the Chl a field is modulated by the vertical velocity, the residual component is modulated by the horizontal velocity components. Vertical velocities are responsible, through coastal upwelling, for Chl a bloom enhancement, while horizontal velocities spread coastal Chl a surface blooms off-shore.
Paraules clau: Keywords: Alboran Sea; chlorophyll; wind forcing; primary production; ocean biogeochemical model; ROMS model; EOF analysis
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Solé J., Emelianov M., Ostrovskii A., Puig P., García-Ladona E. (2016)
Scientia Marina, 80S1, 195-204. DOI: http://dx.doi.org/10.3989/scimar.04322.05A. (BibTeX: sole.etal.2016c)
Resum: Veure
In this work we report short-term measurements of the thermohaline structure and velocity field inside a narrow submarine canyon by means of a yo-yo–like profiler. An Aqualog profiler was deployed inside the Besòs Canyon in the northwestern Mediterranean continental margin, providing a unique data set on the vertical evolution of water column characteristics with unprecedented fine-scale spatial and temporal resolution. The observations reported here show a very dynamic transient short-term response with a complex vertical structure not observed previously in any submarine canyon of this region. The vertical distribution of water masses was characteristic of the western Mediterranean basin with Atlantic waters (AW) at the surface, Western Intermediate waters (WIW) in the middle and Levantine Intermediate (LIW) waters below. Turner angle and empirical orthogonal functions show that double-diffusive and isopycnal mixing are the main dominant processes at small scales. The interfaces of the three layers exhibit highly vertical excursions in relatively short times. At the surface, deepening of AW was observed, associated with flow intensification events. Deeper in the water column, within the submarine canyon confinement, the WIW-LIW interface uplifts about 100-150 m. These motions are associated with relatively up- and down-canyon–enhanced current events (up to 15-20 cm s–1 at 500 and 800 m depths) along the canyon axis. The time scales of the vertical variability were concentrated in a broad band around the semi-diurnal and local inertial frequencies within the WIW and LIW layers.
Paraules clau: fine-scale variability; submarine canyon; yo-yo like profiler; thermohaline structure; AW; WIW; LIW.
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Solé J., Berdalet E., Arin L., Cros Ll., Delgado M., Kuwata A., Llebot C., Marrasé C. (2016)
Scientia Marina, 80, S1, 33-38. DOI: 10.3989/scimar.04520.06D. (BibTeX: sole.etal.2016e)
Resum: Veure
Plankton ecology has been the object of intense research and progress in the last few decades. This has been partly due to technological advances that have facilitated the multidisciplinary and high-resolution sampling of ecosystems and improved experimentation and analytical methodologies, and to sophisticated modelling. In addition, exceptional researchers have had the vision to integrate all these innovative tools to form a solid theoretical background in ecology. Here we provide an overview of the outstanding research work conducted by Professor Marta Estrada and her pioneering contribution to different areas of research in the last four decades. Her research in biological oceanography has mainly focussed on phytoplankton ecology, taxonomy and physiology, the functional structure of plankton communities, and physical and biological interactions in marine ecosystems. She has combined a variety of field and laboratory approaches and methodologies, from microscopy to satellite observations, including in-depth statistical data analysis and modelling. She has been a reference for scientists all over the world. Here, her contributions to plankton ecology are summarized by some of her students and closest collaborators, who had the privilege to share their science and everyday experiences with her.
Paraules clau: Phytoplankton ecology, taxonomy, functional structure of plankton communities, physical-biological interactions, ecología del fitoplancton, taxonomía, estructura funcional de las comunidades plantónicas, interacciones física-biología
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Solé J., García-Ladona E., Piera J., Estrada M. (2016)
Scientia Marina, 80S1, 129-137. DOI: 10.3989/scimar.04271.18A. (BibTeX: sole.etal.2016k)
Resum: Veure
Phytoplankton blooms are events of production and accumulation of phytoplankton biomass that influence ecosystem dynamics and may also have effects on socio-economic activities. Among the biological factors that affect bloom dynamics, prey selection by zooplankton may play an important role. Here we consider the initial state of development of an algal bloom and analyse how a reduced grazing pressure can allow an algal species with a lower intrinsic growth rate than a competitor to become dominant. We use a simple model with two microalgal species and one zooplankton grazer to derive general relationships between phytoplankton growth and zooplankton grazing. These relationships are applied to two common grazing response functions in order to deduce the mathematical constraints that the parameters of these functions must obey to allow the dominance of the lower growth rate competitor. To assess the usefulness of the deduced relationships in a more general framework, the results are applied in the context of a multispecies ecosystem model (ERSEM).
Paraules clau: algal blooms; plankton; prey selection; grazing functions; multispecies model; mathematical constraints.
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García Sotillo M., Garcia-Ladona E., Orfila A., Rodríguez-Rubio P., Cristobal Maraver J., Conti D., Padorno E., Jiménez J.A., Capó E., Pérez F., Sayol J.M., de los Santos F.J., Amo A., Rietz A., Troupin C., Tintore J., Álvarez-Fanjul E. (2016)
Earth System Science Data, 8, 1, 141-149. DOI: 10.5194/essd-8-141-2016. (BibTeX: garciasotillo.etal.2016c)
Resum: Veure
On 9 September 2014, an intensive drifter deployment was carried out in the Strait of Gibraltar. In the frame of the MEDESS-4MS Project (EU MED Program), the MEDESS-GIB experiment consisted of the deployment of 35 satellite tracked drifters, mostly of CODE-type, equipped with temperature sensor sampling at a rate of 30 min. Drifters were distributed along and on both sides of the Strait of Gibraltar. The MEDESS-GIB deployment plan was designed as to ensure quasi-synoptic spatial coverage. To this end, four boats covering an area of about 680 NM2 in 6 h were coordinated. As far as these authors know, this experiment is the most important exercise in the area in terms of number of drifters released. Collected satellite-tracked data along drifter trajectories have been quality controlled and processed to build the presented MEDESS-GIB database. This paper reports the MEDESS-GIB data set that comprises drifter trajectories, derived surface currents and in situ SST measurements collected along the buoys tracks. This series of data is available through the PANGAEA (Data Publisher for Earth and Environmental Science) repository, with the following doi:10.1594/PANGAEA.853701. Likewise, the MEDESS-GIB data will be incorporated as part of the Copernicus Marine historical products. The MEDESS-GIB data set provides a complete Lagrangian view of the surface inflow of Atlantic waters through the Strait of Gibraltar and thus, very useful data for further studies on the surface circulation patterns in the Alboran Sea, and their links with one of the most energetic Mediterranean Sea flows: the Algerian Current.
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Trindade A., Peliz A., Dias J., Lamas L., Oliveira P., Cruz T. (2016)
Continental Shelf Research, 127, 12-27. DOI: 10.1016/j.csr.2016.08.04. (BibTeX: trindade.etal.2016a)
Resum: Veure
With favoredoffshoreanddownstreamadvection,thequestionofwhichphysicalmechanismmay promoteonshoretransportoflarvaeinupwellingsystemsisofcentralinterest.Wehaveconducteda semi-realistic highresolution(0.25km)numericalstudyofLagrangiantransportsacrosstheinner-shelf under upwelling-favorablewindforcingconditions,focusingontheshelfareaoftheSouthwestern Portuguese coast,intheleeofCapeSines.Weaddour findings toseveralyearsofbiologicalobservations of C. montagui, aplanktonicspecieswithhigherrecruitmentduringtheupwellingpeaktimelywiththe daylight flood. Simulationscovera fifteendaysperiodduringthesummerof2006.WefocusedonSpring and Neaptideperiodsandobservedupfrontdifferencesbetweensimulationsandtheinsituobserva- tions. However,themodeliscapableofrepresentingthemaindynamicsoftheregion,namelythere- petitivecharacteroftheinner-shelfcurrents.We find thatthecross-shore flow variessignificantly inthe daily cycle,andlocallywithinascaleofafewkilometersinassociationwithlocaltopographyandthe presence ofthecape.Weconsidertheregionimmediatelyintheleeofthecapetobeanupwelling shadow wherethelarvaebecameretained,andfoundthattidallytiedmigrationprovesbeneficial for successful recruitmentduringthespringtidesperiod.Ourworksuggestedthatthewindisnottheonly mechanism responsibleforthedailyvariabilityofthecross-shoreexchange.However,itssharpreversal at middayiscriticalfortheadvectionoflarvaetowardsthecoast.
Paraules clau: Inner-shelfcirculation Cross-shoretransport Coastal upwelling Lagrangian model Vertical migration
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Turiel A., Piles M., González-Gambau V., Ballabrera-Poy J., Gabarró C., Martínez J., Olmedo E., Portabella M., Pérez F., Solé J. (2016)
Scientia Marina, 80S1, 173-193. DOI: 10.3989/scimar.04291.15A. (BibTeX: turiel.etal.2016h)
Resum: Veure
Summary: Soil Moisture and Ocean Salinity (SMOS) is the first satellite mission capable of measuring sea surface salinity and soil moisture from space. Its novel instrument (the L-band radiometer MIRAS) has required the development of new algorithms to process SMOS data, a challenging task due to many processing issues and the difficulties inherent in a new technology. In the wake of SMOS, a new community of users has grown, requesting new products and applications, and extending the interest in this novel brand of satellite services. This paper reviews the role played by the Barcelona Expert Centre under the direction of Jordi Font, SMOS co-principal investigator. The main scientific activities and achievements and the future directions are discussed, highlighting the importance of the oceanographic applications of the mission.
Paraules clau: SMOS; salinity; ocean circulation; oceanography; soil moisture; sea ice; radiometry; remote sensing
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Vila M., Abós-Herràndiz R., Isern-Fontanet J., Àlvarez J., Berdalet E. (2016)
Scientia Marina, 80, S1, 107-115. (BibTeX: vila.etal.2016)
Resum: Veure
Blooms of the benthic dinoflagellate Ostreopsis have been related to sporadic acute respiratory symptoms and general malaise in people exposed to marine aerosols on some Mediterranean beaches. However, the direct link between recurrent Ostreopsis blooms and health problems has not been clearly established. In order to establish and elucidate the connection, we conducted a joint ecology and epidemiology study in an Ostreopsis hot spot. Throughout the bloom, which extended from the end of June until the end of October 2013, 81% of the human cohort that we studied experienced at least one Ostreopsis-related symptom. Paradoxically, the time when the effects were greatest was during a short time window in early August. This corresponded to the transition from the exponential growth to the stationary phase of the bloom. Negligible symptoms were reported from August to mid-October, during the stationary period of the proliferation, when O. cf. ovata maintained high concentrations of epiphytic cells. No clear patterns in the landward wind component were noted during the time when health effects were greatest. Our main hypothesis is that the irritants present in the aerosol are produced during a particular physiological phase of the Ostreopsis cells during the bloom.
Paraules clau: Ostreopsis, epidemiology, Mediterranean, HAB, dinoflagellates, respiratory irritation, epidemiología, Mediterráneo, proliferaciones algales nocivas, dinoflagelados, irritaciones respiratorias
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Viúdez Á., Fernández-Pedrera M., Rodríguez-Marroyo R. (2016)
Scientia Marina, 80S1, 235-248. DOI: 10.3989/scimar.04297.06B. (BibTeX: viudez.etal.2016a)
Resum: Veure
Offshore wind is proposed as an energy source to upwell nutrient-rich deep water to the ocean photic layers. A spar-buoy wind turbine with a rigid tube about 300 m long is proposed as a pipe to drive deep water up to the surface. The minimum energy required to uplift the water is the potential energy difference between surface waters inside and outside the pipe, which depends on the background density profile. The corresponding surface jump or hydraulic head, h, calculated for several analytical and experimental density profiles, is of the order of 10 cm. If the complete turbine power (of the order of several MW) is used for raising the water (assuming a 100% pump efficiency), in a frictionless flow, very large water volumes, of the order of thousands of m3 s−1, will be transported to the photic layers. In a more realistic case, taking into account pipe friction in wide pipes, of the order of 10 m radius, and a power delivered to the fluid of 1 MW, the volume transport is still very large, about 500 m3 s−1. However, such a large amount of dense water could sink fast to aphotic layers due to vertical static instability (the fountain effect), ruining the enhancement of primary production. Hence, some ways to increase the turbulent entrainment and avoid the fountain effect are proposed. From the energetic viewpoint, artificial upwelling using offshore wind energy is a promising way to fertilize large open sea regions. This mariculture application is, however, severely subjected to atmosphere and ocean climatology, as well as to ecological dynamics. The general problem is multidisciplinary, and some important physical, engineering and ecological questions need to be seriously addressed to improve our confidence in the approach presented here.
Paraules clau: artificial upwelling; mariculture applications; ocean fertilization; offshore wind energy; spar-buoy wind turbine.