Research papers
The current filters are: Starting year = 2022, Ending year = 2023
0 Kb
Caetano L., Guallar C., Martín J., Vidal M., Cotrim da Cunha L., Vieira R., Amora-Nogueira L., Pelegrí J.L., Marotta H. (2023)
Journal of Marine Systems, 239 DOI: 10.1016/j.jmarsys.2023.103858. (BibTeX: caetano.etal.2023)
Abstract: See
Subpolar coastal waters are key hotspots in the global carbon cycle. However, the small-scale distribution of partial pressure of carbon dioxide (pCO2) in these environments and the physical and biological controls underlying this variability are still poorly understood. Here, we examine simultaneous high-resolution spatial measurements of wind speed and pCO2, temperature, salinity, and in-vivo chlorophyll-a fluorescence (chl-a fluo, a proxy of phytoplankton biomass) in surface waters that were obtained during an oceanographic survey in the Argentinian Beagle Channel (subantarctic Atlantic Patagonian) in early fall 2017. The 240 km study transect (centered at 55◦S - 67◦W) was divided into two zones: (A1) The Beagle Channel innermost portion, semi-enclosed and subject to strong continental influence and (A2) its eastern outlet towards the open Southwest Atlantic. Discrete seawater samples were also collected for apparent oxygen utilization (AOU), nutrients and pH measurements. High-resolution spatial measurements revealed the persistence of pCO2 below atmospheric equilibrium, increasing in median (interquartile range 25–75%) from 314 μatm in the inner Beagle Channel (A1) to 348 μatm towards the adjacent open sea (A2). A decrease in atmospheric CO2 sequestration was associated with an increase in water temperature from 9.5 ◦C to 10.7 ◦C, salinity from 30.8 to 32.5, and chl-a fluo from 2.24 to 2.91 mg m− 3 along the coastal-offshore gradient. Low AOU and nutrient levels were found in regions inside the channel. Indeed, the relationships between CO2 and temperature or salinity were significantly different from those expected from the theoretical solubility effect, indicating a dominance of metabolic over physicochemical controls on this gas. Moreover, physical factors such as vertical stratification contributed to the variable surface pCO2 values. These findings reveal the existence of short-scale spatial variability of CO2 in the Beagle Channel, improving our understanding of the multiple controls on atmospheric carbon sequestration in extensive subpolar continental shelves.
Keywords: pCO2 High-resolution spatial variability Patagonia Sub-Antarctic waters Beagle Channel
0 Kb
Fournier S., Bingham F.M., González-Haro C., Hayashi A., Ulfsax-Carlin K.M., Brodnitz S.K., González-Gambau V., Kuusela M. (2023)
Remote Sensing, 15, 422 DOI: 10.3390/rs15020422. (BibTeX: fournier.etal.2023)
Abstract: See
Evaluating and validating satellite sea surface salinity (SSS) measurements is fundamental.
There are two types of errors in satellite SSS: measurement error due to the instrument’s inaccuracy
and problems in retrieval, and sampling error due to unrepresentativeness in the way that the sea
surface is sampled in time and space by the instrument. In this study, we focus on sampling errors,
which impact both satellite and in situ products. We estimate the sampling errors of Level 3 satellite
SSS products from Aquarius, SMOS and SMAP, and in situ gridded products. To do that, we use
simulated L2 and L3 Aquarius, SMAP and SMOS SSS data, individual Argo observations and gridded
Argo products derived from a 12-month high-resolution 1/48◦ ocean model. The use of the simulated
data allows us to quantify the sampling error and eliminate the measurement error. We found that
the sampling errors are high in regions of high SSS variability and are globally about 0.02/0.03 psu at
weekly time scales and 0.01/0.02 psu at monthly time scales for satellite products. The in situ-based
product sampling error is significantly higher than that of the three satellite products at monthly
scales (0.085 psu) indicating the need to be cautious when using in situ-based gridded products to
validate satellite products. Similar results are found using a Correlated Triple Collocation method
that quantifies the standard deviation of products’ errors acquired with different instruments. By
improving our understanding and quantifying the effect of sampling errors on satellite-in situ SSS
consistency over various spatial and temporal scales, this study will help to improve the validation
of SSS, the robustness of scientific applications and the design of future salinity missions.
Keywords: sea surface salinity; SMAP; SMOS; Aquarius; sampling errors
0 Kb
Gabarró C., Hughes N., Wilkinson J., Bertino L., Bracher A., Diehl T., Dierking W., Gonzalez-Gambau V., Lavergne T., Madurell T., Malnes E., Mae Wagner P. (2023)
Frontiers in Remote Sensing, 4 DOI: 10.3389/frsen.2023.952091. (BibTeX: gabarro.etal.2023)
Abstract: See
Improving satellite-based
monitoring of the polar regions:
Identification of research and
capacity gaps
Carolina Gabarró 1 *, Nick Hughes 2 , Jeremy Wilkinson 3 ,
Laurent Bertino 4 , Astrid Bracher 5 , 6
, Thomas Diehl 7 ,
Wolfgang Dierking 8 ,5 , Veronica Gonzalez-Gambau 1 ,
Thomas Lavergne 9 , Teresa Madurell 1 , Eirik Malnes 10 and
Penelope Mae Wagner 2
1 Barcelona Expert Center (BEC) and Institute of Marine Sciences (ICM), Consejo Superior de
Investigaciones Marinas (CSIC), Barcelona, Spain, 2 Norwegian Meteorological Institute, Norwegian Ice
Service, Tromsø, Norway, 3
British Antarctic Survey, Cambridge, United Kingdom, 4 Nansen Environmental
and Remote Sensing Center and Bjerknes Centre for Climate Research, NERSC, Bergen, Norway, 5
Alfred-
Wegener-Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany, 6 Institute of
Environmental Physics, University Bremen, Bremen, Germany, 7
European Commission, Joint Research
Centre, Ispra, Italy, 8 UiT The Arctic University of Norway, Tromsø, Norway, 9 Research and Development
Department, Norwegian Meteorological Institute, Oslo, Norway, 10 NORCE Norwegian Research Centre
AS, Oslo, Norway
We present a comprehensive review of the current status of remotely sensed and
in situ sea ice, ocean, and land parameters acquired over the Arctic and Antarctic
and identify current data gaps through comparison with the portfolio of products
provided by Copernicus services. While we include several land parameters, the
focus of our review is on the marine sector. The analysis is facilitated by the
outputs of the KEPLER H2020 project. This project developed a road map for
Copernicus to deliver an improved European capacity for monitoring and
forecasting of the Polar Regions, including recommendations and lessons
learnt, and the role citizen science can play in supporting Copernicus’
capabilities and giving users ownership in the system. In addition to
summarising this information we also provide an assessment of future satellite
missions (in particular the Copernicus Sentinel Expansion Missions), in terms of the
potential enhancements they can provide for environmental monitoring and
integration/assimilation into modelling/forecast products. We identify possible
synergies between parameters obtained from different satellite missions to
increase the information content and the robustness of specific data products
considering the end-users requirements, in particular maritime safety. We analyse
the potential of new variables and new techniques relevant for assimilation into
simulations and forecasts of environmental conditions and changes in the Polar
Regions at various spatial and temporal scales. This work concludes with several
specific recommendations to the EU for improving the satellite-based monitoring
of the Polar Regions
Keywords: polar observations, satellite remote sensing, Copernicus, citizen science, Arctic, recommendation for stakeholders
0 Kb
Grégoire M., Alvera-Azcaráte A., Buga L., Capet A., Constantin S., D\'ortenzio F., Doxaran D., Faugeras Y., García-Espriu A., Golumbeanu M., González-Haro C., González-Gambau V., Kasprzyk J.P., Ivanov E., , , Mateescu R., Meulders C., Olmedo E., Pons L., Pujol M.I., Sarbu G., Turiel A., Vandenbulcke L., Rio M.H. (2023)
Frontiers in Marine Science, 9, 2862 DOI: 10.3389/fmars.2022.998970. (BibTeX: gregoire.etal.2023)
Abstract: See
In this paper, satellite products developed during the Earth Observation for Science
and Innovation in the Black Sea (EO4SIBS) ESA project are presented. Ocean
colour, sea level anomaly and sea surface salinity datasets are produced for the last
decade and validated with regional in-situ observations. New data processing is
tested to appropriately tackle the Black Sea’s particular configuration and
geophysical characteristics. For altimetry, the full rate (20Hz) altimeter
measurements from Cryosat-2 and Sentinel-3A are processed to deliver a 5Hz
along-track product. This product is combined with existing 1Hz product to
produce gridded datasets for the sea level anomaly, mean dynamic topography,
geostrophic currents. This new set of altimetry gridded products offers a better
definition of the main Black Sea current, a more accurate reconstruction and
characterization of eddies structure, in particular, in coastal areas, and improves
the observable wavelength by a factor of 1.6. The EO4SIBS sea surface salinity from
SMOS is the first satellite product for salinity in the Black Sea. Specific data
treatments are applied to remedy the issue of land-sea and radio frequency
nterference contamination and to adapt the dielectric constant model to the low
salinity and cold waters of the Black Sea. The quality of the SMOS products is
assessed and shows a significant improvement from Level-2 to Level -3 and Level 4 products. Level-4 products accuracy is 0.4-0.6 psu, a comparable value to that in
the Mediterranean Sea. On average SMOS sea surface salinity is lower than salinity
measured by Argo floats, with a larger error in the eastern basin. The adequacy of
SMOS SSS to reproduce the spatial characteristics of the Black Sea surface salinity
and, in particular, plume patterns is analyzed. For ocean colour, chlorophyll-a,
turbidity and suspended particulate materials are proposed using regional
calibrated algorithms and satellite data provided by OLCI sensor onboard
Sentinel-3 mission. The seasonal cycle of ocean colour products is described
and a water classification scheme is proposed. The development of these three
types of products has suffered from important in-situ data gaps that hinder a sound
calibration of the algorithms and a proper assessment of the datasets quality. We
propose recommendations for improving the in-situ observing system that will
support the development of satellite products.
Keywords: satellite, ocean colour, altimetry, salinity, Black Sea, environment monitoring, observing system
0 Kb
Roget E., Pelegrí J.L., Planella-Morato J., Puigdefàbregas J., Emelianov M., Vallès-Casanova I., Orúe-Echevarria D. (2023)
Progress in Oceanography, 211, 102968 DOI: 10.1016/j.pocean.2023.102968. (BibTeX: roget.etal.2023)
Abstract: See
Diapycnal mixing in the Brazil-Malvinas Confluence Zone (BMC) is assessed on the basis of microstructure measurements done as part of an April 2017 cruise, which explored the mesoscalar and regional frontal dynamics. Sampling was done down to 400 m in 11 locations on both sides of the BMC, over the slope and in the abyssal waters. Turbulent scales, non-dimensional numbers, energy dissipation rates and diapycnal eddy diffusivities are calculated, which allow us to assess the state of the small-scale turbulence in the frontal region.
Active turbulence was present at all depths and stations, with high-dissipation patches ranging from several metres to a few tens of metres. The frontal zone is characterized by high energy dissipation and eddy diffusivity. The geometric mean eddy diffusivity for all stations and the entire water column is 7.0 × 10-4 m2 s−1. The mean values halve when only considering the more stratified seasonal thermocline, 3.8 × 10-4 m2 s−1, and are twice larger south than north of the BMC.
High dissipation rates coincide with high vertical shear, possibly related to the convergence of the two intense currents and/or the generation of internal waves by the associated mesoscalar and submesoscalar features. The layered structures related to intruding filaments favor double diffusive convection and salt fingering. Near-bottom mixing at the stations on the continental slope is possible related to shear-driven Kelvin-Helmoltz instabilities.
0 Kb
Xie J., Raj R.P., Bertino L., Martínez J., Gabarro C., Catany R. (2023)
Ocean Science, 19, 269-287. DOI: 10.5194/os-19-269-2023. (BibTeX: xie.etal.2023)
Abstract: See
In the Arctic, the sea surface salinity (SSS) plays
a key role in processes related to water mixing and sea ice.
However, the lack of salinity observations causes large un-
certainties in Arctic Ocean forecasts and reanalysis. Recently
the Soil Moisture and Ocean Salinity (SMOS) satellite mis-
sion was used by the Barcelona Expert Centre to develop an
Arctic SSS product. In this study, we evaluate the impact of
assimilating this data in a coupled ocean–ice data assimila-
tion system. Using the deterministic ensemble Kalman filter
from July to December 2016, two assimilation runs respec-
tively assimilated two successive versions of the SMOS SSS
product on top of a pre-existing reanalysis run. The runs were
validated against independent in situ salinity profiles in the
Arctic. The results show that the biases and the root-mean-
squared differences (RMSD) of SSS are reduced by 10 % to
50 % depending on the area and highlight the importance of
assimilating satellite salinity data. The time series of fresh-
water content (FWC) further shows that its seasonal cycle
can be adjusted by assimilation of the SSS products, which
is encouraging of the assimilation of SSS in a long-time re-
analysis to better reproduce the Arctic water cycle.
0 Kb
Biguino B., Olmedo E., Ferreira A., Zacarias N., Lamas L., Favareto L., Palma C., Borges C., Teles-Machado A., Dias J., Castellanos P., Brito A.C. (2022)
Remote Sensing, 14, 2, 423. DOI: 10.3390/rs14020423. (BibTeX: biguino.etal.2022)
Abstract: See
Salinity is one of the oldest parameters being measured in oceanography and one of the most important to study in the context of climate change. However, its quantification by satellite remote sensing has been a relatively recent achievement. Currently, after over ten years of data gathering, there are still many challenges in quantifying salinity from space, especially when it is intended for coastal environments study. That is mainly due to the spatial resolution of the available products. Recently, a new higher resolution (5 km) L4 SMOS sea surface salinity (SSS) product was developed by the Barcelona Expert Center (BEC). In this study, the quality of this product was tested along the Western Iberian Coast through its comparison with in situ observations and modelled salinity estimates (CMEMS IBI Ocean Reanalysis system). Moreover, several parameters such as the temperature and depth of in situ measurements were tested to identify the variables or processes that induced higher errors in the product or influenced its performance. Lastly, a seasonal and interannual analysis was conducted considering data between 2011 to 2019 to test the product as a potential tool for long-term studies. The results obtained in the present analysis showed a high potential of using the L4 BEC SSS SMOS product in extended temporal and spatial analyses along the Portuguese coast. A good correlation between the satellite and the in situ datasets was observed, and the satellite dataset showed lower errors in retrieving coastal salinities than the oceanic model. Overall, the distance to the coast and the closest rivers were the factors that most influenced the quality of the product. The present analysis showed that great progress has been made in deriving coastal salinity over the years and that the SMOS SSS product is a valuable contribution to worldwide climatological studies. In addition, these results reinforce the need to continue developing satellite remote sensing products as a global and cost-effective methodology for long-term studie
Keywords: surface salinity, SMOS, coastal ocean, CMEMS IBI Ocean reanalysis system, climate change
0 Kb
Campuzano F., Santos F., Simionesei L., Oliveira A.R., Olmedo E., Turiel A., Fernandes R., Brito D., Alba M., Novellino A., Neves R. (2022)
Journal of Marine Science and Engineering, 10, 852 DOI: 10.3390/jmse10070852. (BibTeX: campuzano.etal.2022)
Abstract: See
The coupling of coastal or regional ocean models to hydrological models or observed data is currently an uncommon practice in operational oceanography. Though hydrological models are regarded as a powerful and useful tool for estimating the quantity and quality of freshwater running in a watershed, they fail to provide accurate results for river flow reaching the coastal area due to water-management activities occurring within the river catchment, activities such as human consumption, irrigation, storage, etc. For this reason, many coastal and regional ocean models continue to impose surface zero-salinity discharges as land boundary conditions for representing such a dynamic boundary. Moreover, river flows are based in climatologies, thus neglecting seasonal and interannual variability. To achieve those objectives, this study proposes an integrated methodology ranging from watershed models to validation in the coastal area and passing through methods and proxies for integrating the freshwater flows into regional ocean models. The main objective of this study is to explore the results obtained by using more sophisticated land boundary conditions based on the capacities of state-of-the-art hydrologic models combined with observation networks. In addition to the evaluation of the source of river-flow data, this work also explores the use of estuarine proxies based on simple modelling grids. The estuarine proxies enable the incorporation of the mixing processes that take place in estuaries into the land fluxes and obtain the plume momentum. The watershed, estuarine proxies, and ocean were modelled using the MOHID Water modelling system and evaluated in western Iberia waters. The modelling results served to illustrate the sea surface salinity extension of the Western Iberia Buoyant Plume (WIBP) during an extreme event in March 2018.
Keywords: freshwater discharges; operational oceanography; sea surface salinity; IBI region; land boundary; estuarine proxy; water continuum; numerical models
0 Kb
Cazzaniga I., Zibordi G., Mélin F., Kwiatkowska E., Talone M., Dessailly D., Gossn J.I., Müller D. (2022)
IEEE Geoscience and Remote Sensing Letters, 19, 1-5. DOI: 10.1109/LGRS.2021.3136291. (BibTeX: cazzaniga.etal.2022)
Abstract: See
Radiometric water products from the Neural Network (NNv2) in the Alternative Atmospheric Correction (AAC) processing chain of Ocean and Land Colour Instruments (OLCI) were assessed over different marine regions. These products, not included among the operational ones, were custom produced from the Copernicus Sentinel-3 OLCI Baseline Collection 3. The assessment benefitted of in situ reference data from the Ocean Color component of the Aerosol Robotic Network (AERONET-OC) from sites representative of different water types. These included clear waters in the Western Mediterranean Sea, optically-complex waters characterized by varying concentrations of total suspended matter and chromophoric dissolved organic matter (CDOM) in the northern Adriatic Sea, and optically-complex waters characterized by very high concentrations of CDOM in the Baltic Sea. The comparison of the water-leaving radiances 𝑳𝑾𝑵 derived from OLCI data on board Sentinel-3A and Sentinel-3B with those from AERONETOC confirmed consistency between the products from the two satellite sensors. However, the accuracy of satellite data products exhibited dependence on the water type. A general underestimate of 𝑳𝑾𝑵 was observed for clear waters. Conversely, overestimates were observed for data products from optically-complex waters with the worst results obtained for CDOM-dominated waters. These findings suggest caution in exploiting NNv2 radiometric products, especially for highly absorbing and
clear waters.
Keywords: Remote Sensing, Ocean Color, Validation
0 Kb
Gabarró C., Fabregat P., Hernández-Maciá F., Jove R., Salvador J., Spreen G., Thielke L., Dadic R., Huntemann M., Kolabutin N., Nomura D., Hannula H.R., Schneebeli M. (2022)
Elementa: Science of the Anthropocene, 10, 1 DOI: 10.1525/elementa.2022.00031. (BibTeX: gabarro.etal.2022)
Abstract: See
Arctic sea ice is changing rapidly. Its retreat significantly impacts Arctic heat fluxes, ocean currents, and ecology, warranting the continuous monitoring and tracking of changes to sea ice extent and thickness. L-band (1.4 GHz) microwave radiometry can measure sea ice thickness for thin ice 1 m, depending on salinity and temperature. The sensitivity to thin ice makes L-band measurements complementary to radar altimetry which can measure the thickness of thick ice with reasonable accuracy. During the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, we deployed the mobile ARIEL L-band radiometer on the sea ice floe next to research vessel Polarstern to study the sensitivity of the L-band to different sea ice parameters (e.g., snow and ice thickness, ice salinity, ice and snow temperature), with the aim to help improve/validate current microwave emission models. Our results show that ARIEL is sensitive to different types of surfaces (ice, leads, and melt ponds) and to ice thickness up to 70 cm when the salinity of the sea ice is low. The measurements can be reproduced with the Burke emission model when in situ snow and ice measurements for the autumn transects were used as model input. The correlation coefficient for modeled Burke brightness temperature (BT) versus ARIEL measurements was approximately 0.8. The discrepancy between the measurements and the model is about 5%, depending on the transects analyzed. No explicit dependence on snow depth was detected. We present a qualitative analysis for thin ice observations on leads. We have demonstrated that the ARIEL radiometer is an excellent field instrument for quantifying the sensitivity of L-band radiometry to ice and snow parameters, leading to insights that can enhance sea ice thickness retrievals from L-band radiometer satellites (such as Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP)) and improve estimates of Arctic sea-ice thickness changes on a larger scale
Keywords: Radiometry, Arctic, Emissivity, Sea ice, SMOS
0 Kb
Gimeno J., Jorba À., Nicolás B., Olmedo E. (2022)
SIAM Journal on Applied Dynamical Systems, 21, 3, 1832-1861. DOI: 10.1137/21M1458363. (BibTeX: gimeno.etal.2022)
Abstract: See
In this paper we present a procedure to compute reducible invariant tori and their stable and
unstable manifolds in Poincar´e maps. The method has two steps. In the first step we compute, by
means of a quadratically convergent scheme, the Fourier series of the torus, its Floquet transformation,and its Floquet matrix. If the torus has stable and/or unstable directions, in the second step we compute the Taylor-Fourier expansions of the corresponding invariant manifolds up to a given order. The paper also discusses the case in which the torus is highly unstable so that a multiple shooting strategy is needed to compute the torus. If the order of the Taylor expansion of the manifolds is fixed and N is the number of Fourier modes, the whole computational effort (torus and manifolds) increases as OpN log Nq and the memory required behaves as OpNq. This makes the algorithm very suitable to compute high-dimensional tori for which a huge number of Fourier modes are needed. Besides, the algorithm has a very high degree of parallelism. The paper includes examples where we compute invariant tori (of dimensions up to 5) of quasi-periodically forced ODEs. The computations are run in a parallel computer and its efficiency with respect to the number of processors is also discussed.
Keywords: Parametrization method, Quasi-periodic Floquet Theory, Jet transport, and Parallel computing
0 Kb
González-Gambau V., Olmedo E., Turiel A., González-Haro C., García-Espriu A., Martínez J., Alenius P., Tuomi L., Catany R., Arias M., Gabarró C., Hoareau N., Umbert M., Sabia R., Fernández D. (2022)
Earth System Science Data, 14, 2343-2368. DOI: 10.5194/essd-14-2343-2022. (BibTeX: gonzalezgambau.etal.2022)
Abstract: See
This paper presents the first Soil Moisture and Ocean Salinity (SMOS) Sea Surface Salinity (SSS) dedicated products over the Baltic Sea. The SSS retrieval from L-band brightness temperature (TB) measurements over this basin is really challenging due to important technical issues, such as the land–sea and ice–sea contamination, the high contamination by radio-frequency interference (RFI) sources, the low sensitivity of L-band TB at SSS changes in cold waters, and the poor characterization of dielectric constant models for the low SSS range in the basin. For these reasons, exploratory research in the algorithms used from the level 0 up to level 4 has been required to develop these dedicated products. This work has been performed in the framework of the European Space Agency regional initiative Baltic+ Salinity Dynamics. Two Baltic+ SSS products have been generated for the period 2011–2019 and are freely distributed: the Level 3 (L3) product (daily generated 9 d maps in a 0.25◦ grid; https://doi.org/10.20350/digitalCSIC/13859, González-Gambau et al., 2021a) and the Level 4 (L4) product (daily maps in a 0.05◦ grid; https://doi.org/10.20350/ digitalCSIC/13860, González-Gambau et al., 2021b), which are computed by applying multifractal fusion to L3 SSS with SST maps. The accuracy of L3 SSS products is typically around 0.7–0.8 psu. The L4 product has an improved spatiotemporal resolution with respect to the L3 and the accuracy is typically around 0.4 psu. Regions with the highest errors and limited coverage are located in Arkona and Bornholm basins and Gulfs of Finland and Riga. The impact assessment of Baltic+ SSS products has shown that they can help in the understanding of salinity dynamics in the basin. They complement the temporally and spatially very sparse in situ measurements, covering data gaps in the region, and they can also be useful for the validation of numerical models, particularly in areas where in situ data are very sparse.
0 Kb
Grieco G., Stoffelen A., Verhoef A., Vogelzang J., Portabella M. (2022)
Remote Sensing, 14, 21, 5444. DOI: 10.3390/rs14215444. (BibTeX: grieco.etal.2022)
Abstract: See
The normalized standard deviation (Kp) of the noise that affects scatterometer Normalized
Radar Cross-Sections (σ0s) plays a key role in the ocean and more in particular coastal wind retrieval
procedures and the a posteriori quality control. This paper presents a method based on SeaWinds
measurements to estimate Kps. The method computes the standard deviation of the differences
between the full-resolution (slice) σ0s and the footprint (egg) σ0. The results are compared to the
median of Kps provided with SeaWinds σ0s, showing some non-negligible differences. Kps estimated
on non-homogeneous surfaces are larger than those estimated on sea, whereas no differences are
appreciated in the provided Kps, which is likely due to the ability of this methodology to account for
the effect of the scene variability in the estimates. The presence of inter-slice biases is demonstrated
with a trend with the antenna azimuth angle. A multi-collocation slice cross-calibration procedure is
suggested for the retrieval stage. Finally, a theoretical model of the distribution of σ0s is proposed
and used to validate Kps. The results prove the efficacy of this model and that the provided Kps seem
to be largely underestimated at low-wind regimes.
Keywords: SeaWinds; normalized radar cross-section noise; wind
0 Kb
Isern-Fontanet J., Capet X., Turiel A., Olmedo E., González-Haro C. (2022)
Geophysical Research Letters, 49 DOI: 10.1029/2022GL098038. (BibTeX: isernfontanet.etal.2022)
Abstract: See
The contribution of ocean fronts to the properties and temporal evolution of Sea Surface
Temperature (SST) structure functions have been investigated using a numerical model of the California Current system. First, the intensity of fronts have been quantified by using singularity exponents. Then, leaning on the multifractal theory of turbulence, we show that the departure of the scaling of the structure functions from a straight line, known as anomalous scaling, depends on the intensity of the strongest fronts. These fronts, at their turn, are closely related to the seasonal change of intensity of the coastal upwelling characteristics of this area. Our study points to the need to correctly reproduce the intensity of the strongest fronts and, consequently, properly model processes such as coastal upwelling in order to reproduce SST statistics in ocean models.
0 Kb
King G.P., Portabella M., Lin W., Stoffelen A. (2022)
Remote Sensing, 14, 5, 1147. DOI: 10.3390/rs14051147. (BibTeX: king.etal.2022)
Abstract: See
Air–sea fluxes are greatly enhanced by the winds and vertical exchanges generated by
mesoscale convective systems (MCSs). In contrast to global numerical weather prediction models, space-borne scatterometers are able to resolve the small-scale wind variability in and near MCSs at the ocean surface. Downbursts of heavy rain in MCSs produce strong gusts and large divergence and vorticity in surface winds. In this paper, 12.5 km wind fields from the ASCAT-A and ASCAT-B tandem mission, collocated with short time series of Meteosat Second Generation 3 km rain fields, are used to quantify correlations between wind divergence and rain in the Inter-Tropical Convergence Zone (ITCZ) of the Atlantic Ocean. We show that when there is extreme rain, there is extreme convergence/divergence in the vicinity. Probability distributions for wind divergence and rain rates were found to be heavy-tailed: exponential tails for wind divergence (P∼e −αδ with slopes that flatten with increasing rain rate), and power-law tails for rain rates (P∼(R ∗ ) −β with a slower and approximately equal decay for the extremes of convergence and divergence). Co-occurring points are tabulated in two-by-two contingency tables from which cross-correlations are calculated in terms of the odds and odds ratio for each time lag in the collocation. The odds ratio for extreme convergence and extreme divergence both have a well-defined peak. The divergence time lag is close to zero, while it is 30 min for the convergence peak, implying that extreme rain generally appears after (lags) extreme convergence. The temporal scale of moist convection is thus determined by the slower updraft process, as expected. A structural analysis was carried out that demonstrates consistency with the known structure of MCSs. This work demonstrates that (tandem) ASCAT winds are well suited for air–sea exchange studies in moist convection
Keywords: air–sea interaction; scatterometer winds; ASCAT; Meteosat Second Generation; ocean wind divergence; tropical convection; mesoscale convective systems; compound extremes; heavytailed PDFs
0 Kb
Latasa M., Scharek R., Anxelu X., Morán G., Gutiérrez-Rodríguez A., Emelianov M., Salat J., Vidal M., Estrada M. (2022)
Progress in Oceanography, 201, 102737 DOI: 10.1016/j.pocean.2021.102737. (BibTeX: latasa.etal.2022)
Abstract: See
A detailed study of phytoplankton composition and dynamics was carried out during three contrasting situations (cruises F1, F2, and F3) in the northwestern (NW) Mediterranean Sea. Haptophytes, diatoms, and green algae dominated in F1, during the spring bloom, with high nutrients and high phytoplankton biomass. In F2, the postbloom situation with a still weak stratification and lower nutrient concentrations, we found a high spatial variability. Stations were clearly dominated by either Synechococcus, haptophytes or cryptophytes; with Syn echococcus reaching the highest abundance (4 × 105 cells mL− 1, 60% of the integrated chlorophyll a) reported to date for the open Mediterranean Sea. Cryptophytes accumulated close to the surface in very shallow mixed layer stations. In late summer, F3 revealed a fully developed stratification with low nutrients and a marked deep chlorophyll maximum (DCM). Prochlorococcus was present only during this cruise, mainly in deep layers together with haptophytes and pelagophytes, while haptophytes and Synechococcus dominated the upper mixed layer. Flow cytometry (FCM) and pigment-based abundance estimates for Prochlorococcus, Synechococcus and cryptophytes were well correlated, as happened also between small picoeukaryotes (FCM) and green algae (pigments), and between large picoeukaryotes (FCM) and haptophytes (pigments). Dinoflagellate abundance by microscopy and by pigments did not agree well, probably due to the presence of heterotrophic forms or because they contained pigments other than peridinin, the standard dinoflagellate marker. The decrease in size of the FCM large picoeukaryotes group with depth was presumably related to the increasing contribution of pelagophytes, with smaller cells than haptophytes, the other main component of this fraction. Cell size increase of Prochlorococcus and Synechococcus with depth suggests vertical segregation of genotypes or photoadaptation. The groups’ ecological preferences are presented with respect to depth and nutrient concentrations. Synechococcus and cryptophytes occupied shallow layers; diatoms, green algae and Prochlorococcus showed a tendency for deep layers and pelagophytes for even deeper layers, while haptophyte and dinoflagellate allocations were less clear. As for nutrients, the maximum relative contributions of green algae and especially diatoms occurred when dissolved inorganic phosphorus (DIP) concentrations were highest, of Prochlorococcus, dinoflagellates and pelagophytes when lowest, and of Synechococcus and cryptophytes when DIP concentrations were low but not minimal. The contribution of haptophytes did not show a relationship with DIP concentration. These results from individual groups stand as significant exceptions to the general relationship between phytoplankton cell size and nutrient availability.
Keywords: HPLC CHEMTAX Spring bloom Synechococcus bloom Ecological preferences Size distribution
0 Kb
Lin W., Portabella M. (2022)
IEEE Transactions on Geoscience and Remote Sensing, 60, 1-10. DOI: 10.1109/TGRS.2022.3228317. (BibTeX: lin.portabella.2022)
Abstract: See
Recent advances in the sea surface wind quality
control of the Advanced Scatterometer (ASCAT) show that
spatial wind variability within a resolution cell of 25 km 25 km,
namely the subcell wind variability, is highly correlated with the
ASCAT quality indicators, such as the wind inversion residual
(maximum likelihood estimator, MLE) and the singularity
exponent (SE) derived from singularity analysis. This opens up
opportunities for quantifying the instantaneous spatial wind
variability over the global sea surface. In this paper, it is assumed
that the spatial wind variability is linearly proportional to the
temporal variation of buoy sea surface winds time-series
following the Taylor’s hypothesis. As such, the moored buoy
winds with 10-minute sampling are used to examine the subcell
wind variability. Then the sensitivity of ASCAT quality
indicators to the subcell wind variability is evaluated. The results
indicate that although SE is more sensitive than MLE in
characterizing the wind variability, they are mainly
complementary in flagging the most variable winds.
Consequently, an empirical model is derived to relate the buoy
wind vector variability to the ASCAT MLE and/or SE values.
Although the overall procedure is based on the one-dimensional
temporal analysis and such empirical model cannot fully
represent the two-dimensional spatial variability, it leads for the
first time to the development of an ASCAT-derived local wind
variability product. The empirical method presented here is
straightforward and can be applied to other scatterometer
systems.
Keywords: Advanced Scatterometer (ASCAT), wind variability, maximum likelihood estimator (MLE), singularity exponent (SE), subcell
0 Kb
Liu S., Lin W., Portabella M., Wang Z. (2022)
Remote Sensing, 14, 4, 1035. DOI: 10.3390/rs14041035. (BibTeX: liu.etal.2022)
Abstract: See
The estimation of tropical cyclone (TC) intensity using Ku-band scatterometer data is
challenging due to rain perturbation and signal saturation in the radar backscatter measurements. In this paper, an alternative approach to directly taking the maximum scatterometer-derived wind speed is proposed to assess the TC intensity. First, the TC center location is identified based on the unique characteristics of wind stress divergence/curl near the TC core. Then the radial extent of 17-m/s winds (i.e., R17) is calculated using the wind field data from the Haiyang-2B (HY-2B) scatterometer (HSCAT). The feasibility of HSCAT wind radii in determining TC intensity is evaluated using the maximum sustained wind speed (MSW) in the China Meteorological Administration best-track database. It shows that the HSCAT R17 value generally better correlates with the best-track MSW than the HSCAT maximum wind speed, therefore indicating the potential of using the HSCAT data to improve the TC nowcasting capabilities.
Keywords: scatterometer; tropical cyclone; wind radii; intensity; HY-2 satellite
0 Kb
Lloret J., Turiel A., Solé J., Berdalet E., Sabatés A., Olivares A., Gili J.M., Vila-Subirós J., Sardá R. (2022)
Science of The Total Environment, 824, 153803 DOI: 10.1016/j.scitotenv.2022.153803. (BibTeX: lloret.etal.2022)
Abstract: See
The need for alternative energy systems like offshore wind power to move towards the Green Deal objectives is undeniable. However, it is also increasingly clear that biodiversity loss and climate change are interconnected issues that
must be tackled in unison. In this paper we highlight that offshore wind farms (OWF) in the Mediterranean Sea (MS) pose serious environmental risks to the seabed and the biodiversity of many areas due to the particular ecological and socioeconomic characteristics and vulnerability of this semi-enclosed sea. The MS hosts a high diversity of species and habitats, many of which are threatened. Furthermore, valuable species, habitats, and seascapes for citizens\' health and well-being coexist with compounding effects of other economic activities (cruises, maritime transport, tourism activities, fisheries and aquaculture) in a busy space on a narrower continental shelf than in other European seas. We argue that simply importing the OWF models from the northern European seas, which are mostly based on large scale projects, to other seas like the Mediterranean is not straightforward. The risks of implementing these wind farms in the MS have not yet been well evaluated and, considering the Precautionary Principle incorporated into the Marine Strategy Framework Directive and the Maritime Spatial Planning Directive, they should not be ignored. We propose that OWF development in the MS should be excluded from high biodiversity areas containing sensitive and threatened species and habitats, particularly those situated inside or in the vicinity of Marine Protected Areas or areas with valuable seascapes. In the absence of a clearer and comprehensive EU planning of wind farms in the MS, the trade-off between the benefits (climate goals) and risks (environmental and socioeconomic impacts) of OWF could be unbalanced in favor of the risks
Keywords: Offshore energy Marine protected areas, environmental impacts, biodiversity Maritime spatial planning, seascape Renewable energy Mediterranean Sea
0 Kb
Marín-Beltrán I., Demaria F., Ofelio C., Serra L.M., Turiel A., Ripple W.J., Mukul S.A., Costa M.C. (2022)
Science of The Total Environment, 811, 151359 DOI: 10.1016/j.scitotenv.2021.151359. (BibTeX: marinbeltran.etal.2022)
Abstract: See
The metabolism of contemporary industrialized societies, that is their energy and material flows, leads to the overconsumption and waste of natural resources, two factors often disregarded in the global ecological equation. In this Discussion article, we examine the amount of natural resources that is increasingly being consumed and wasted by humanity, and propose solutions to reverse this pattern. Since the beginning of the 20th century, societies, especially from industrialized countries, have been wasting resources in different ways. On one hand, the metabolism of industrial societies relies on non-renewable resources. On the other hand, yearly, we directly waste or mismanage around 78% of the total water withdrawn, 49% of the food produced, 31% of the energy produced, 85% of ores and 26% of non-metallic minerals extracted, respectively. As a consequence, natural resources are getting depleted and ecosystems polluted, leading to irreversible environmental changes, biological loss and social conflicts. To reduce the anthropogenic footprint in the planet, and live in harmony with other species and ourselves, we suggest to shift the current economic model based on infinite growth and reduce inequality between and within countries, following a degrowth strategy in industrialized countries. Public education to reduce superfluous consumption is also necessary. In addition, we propose a set of technological strategies to improve the management of natural resources towards circular economies that, like ecosystems, rely only upon renewable resources.
0 Kb
Martínez J., Gabarró C., Turiel A., González-Gambau V., Umbert M., Hoareau N., González-Haro C., Olmedo E., Arias M., Catany R., Bertino L., Raj R.P., Xie J., Sabia R., Fernández D. (2022)
Earth System Science Data, 14, 1, 307–323. DOI: 10.5194/essd-14-307-2022. (BibTeX: martinez.etal.2022)
Abstract: See
Measuring salinity from space is challenging since the sensitivity of the brightness temperature (TB) to sea surface salinity (SSS) is low (about 0.5 K psu−1 ), while the SSS range in the open ocean is narrow (about 5 psu, if river discharge areas are not considered). This translates into a high accuracy requirement of the radiometer (about 2–3 K). Moreover, the sensitivity of the TB to SSS at cold waters is even lower (0.3 K psu−1 ), making the retrieval of the SSS in the cold waters even more challenging. Due to this limitation, the ESA launched a specific initiative in 2019, the Arctic+Salinity project (AO/1-9158/18/I-BG), to produce an enhanced Arctic SSS product with better quality and resolution than the available products. This paper presents the methodologies used to produce the new enhanced Arctic SMOS SSS product (Martínez et al., 2019) . The product consists of 9 d averaged maps in an EASE 2.0 grid of 25 km. The product is freely distributed from the Barcelona Expert Center (BEC, http://bec.icm.csic.es/, last access: 25 January 2022) with the DOI number https://doi.org/10.20350/digitalCSIC/12620 (Martínez et al., 2019). The major change in this new product is its improvement of the effective spatial resolution that permits better monitoring of the mesoscale structures (large than 50 km), which benefits the river discharge monitoring.
0 Kb
Martínez J., García-Ladona E., Ballabrera-Poy J., Isern-Fontanet J., González-Motos S., Allegue J.M., González-Haro C. (2022)
Journal of Operational Oceanography DOI: 10.1080/1755876X.2022.2102357. (BibTeX: martinez.etal.2022b)
Abstract: See
Sea surface currents probably are the most relevant essential ocean variable affecting diverse
societal challenges concerning the marine environmental (as, for example, safe and efficient
navigation, marine pollution and ecological connectivity). This work introduces a climatological
Atlas (monthly resolution) of currents in the Mediterranean and Canary–Iberian–Biscay basins,
based on today’s state of the art reanalyses of the ocean circulation. The focus is on surface and
subsurface reanalyses (here understood as z 0.5 and z 15 m, respectively) provided by the
Copernicus Marine Environment Monitoring Service (CMEMS). The climatological values are
computed from the median of the empirical probability density functions and the Atlas also
includes the variance matrix and a bimodality index to have quantitative information on their
variability. For both domains, the subsurface climatological fields are reasonably consistent with
circulation schemes proposed in the previous literature but clearly improving the time and
space resolution of the emerging patterns. For the Canary–Iberian–Biscay domain, the monthly
climatological surface currents capture accurately the characteristic seasonal signal and its
transition between a favourable and non-favourable upwelling regime. In the Mediterranean
basin, differences between the near-surface and the 15 m velocity fields suggest a non-
negligible role of winds over the variability of the uppermost ocean layer, specially in the
Eastern Mediterranean basin. This is, up to our knowledge, the first time that such near-surface
climatological patterns are computed. It has been found that, in general, the resulting patterns
agree with surface drifter trajectories. In several regions, interannual variability foster bimodal
and multimodal probability distributions. The Atlas has been conceived with the purpose of
providing a first quantitative assessment on the surface circulation, thus being a
complementary tool of real-time ocean forecasting systems. The Atlas is distributed following
the FAIR principles and is accompanied with a digital version, with enhanced visualization
capabilities for both research and assessment
Keywords: Currents, climatology, atlas, Mediterranean, Atlantic, Iberian; Canary, Biscay
0 Kb
Miracca-Lage M., González-Haro C., Campagnoli-Napolitano D., Isern-Fontanet J., Simionatto-Polito P. (2022)
Journal of Geophysical Research: Oceans, 127 DOI: 10.1029/2021JC018001. (BibTeX: miraccalage.etal.2022)
Abstract: See
Satellite altimeters provide quasi-global measurements of sea surface height, and from those the vertically integrated geostrophic velocity can be directly estimated, but not its vertical structure. This study discusses whether the mesoscale (30–400 km) dynamics of three regions in the South Atlantic can be described by the surface quasi-geostrophic (SQG) theory, both at the surface and in depth, using outputs from an ocean general circulation model. At these scales, the model surface eddy kinetic energy (EKE) spectra show slopes close to k−5/3 (k−3) in winter (summer), characterizing the SQG and quasi-geostrophic (QG) turbulence regimes. We use surface density and temperature to (a) reconstruct the stream function under the SQG theory, (b) assess its capability of reproducing mesoscale motions, and (c) identify the main parameters that improve such reconstruction. For mixed layers shallower than 100 m, the changes in the mixed-layer depth contributes nine times more to the surface SQG reconstruction than the EKE, indicating the strong connection between the quality of the reconstruction and the seasonality of the mixed layer. To further explore the reconstruction vertical extension, we add the barotropic and first baroclinic QG modes to the surface solution. The SQG solutions reproduce the model density and geostrophic velocities in winter, whereas in summer, the interior QG modes prevail. Together, these solutions can improve surface correlations (>0.98) and can depict spatial patterns of mesoscale structures in both the horizontal and vertical domains. Improved spatial resolution from upcoming altimeter missions poses a motivating scenario to extend our findings into future observational studies.
0 Kb
Moreno G., Salvador J., Zudaire I., Murua J., Pelegrí J.L., Uranga J., Murua H., Grande M., Santiago J., Restrepo V. (2022)
Marine Policy, 147 DOI: https://doi.org/10.1016/j.marpol.2022.105352. (BibTeX: moreno.etal.2022)
Abstract: See
Fishers and scientists in the tropical Pacific, Atlantic and Indian Oceans are jointly designing biodegradable fish aggregating devices (bio-FADs) that are efficient for fishing. The tactic followed by most fishers to construct bioFADs is to maintain the same conventional drifting FAD (dFAD) design (i.e., large, submerged net panels hanging from a floating raft) but replacing plastic ropes and netting with organic ropes and canvases. Results from these experiences show that the lifetime of bio-FADs made with conventional FAD designs is notably shorter than what fishers require, thus precluding their adoption. The short lifespan of these bio-FADs is due to the inefficient design of conventional dFADs, which results in major structural stress. Thus, to successfully replace plastic with organic materials and increase the lifespan of bio-FADs, a paradigm shift is needed. Bio-FAD structures should be re-designed to minimize structural stress in the water. The present study summarizes what we have learned from testing bio-FADs in the three tropical oceans, and it proposes a new concept in dFAD design, the jelly-FAD. Mirroring jellyfish, this new dFAD design will aim for quasi-neutral buoyancy, which should reduce (i) the structural stress of the FAD at sea and (ii) the need for additional plastic flotation. The jelly-FAD is not necessarily a fixed design; it is more of a change in the concept of conventional dFAD construction. Preliminary results show that jelly-FADs aggregate tuna as well as conventional FADs do, with lifespans greater than 6 months at sea. In addition, the jelly-FAD showed average drifting speeds similar to a conventional dFAD. To accelerate the adoption of bio-FADs worldwide, recommendations for jelly-FAD construction and tests are provided
Keywords: Fish Aggregating Devices Ecosystem impact Ghost fishing FAD Biodegradable Tuna fisheries ALDFG Marine Pollution
0 Kb
Nicolaus M., Perovich D.K., Spreen G., Granskog M.A., von Albedyll L., Angelopoulos M., Anhaus P., Arndt S., Belter H.J., Bessonov V., , Brauchle J., Calmer R., Cardellach E., Cheng B., , Dadic R., Damm E., de Boer G., Demir O., Dethloff K., Divine D.V., Fong A.A., Fons S., Frey M.M., Fuchs N., Gabarró C., , Goessling H.F., Gradinger R., Haapala J., Haas C., , Hannula H.R., Hen.dricks S, Herber A., Heuzé C., , Hoyland K.V., Huntemann M., Hutchings J.K., Hwang B., , Jacobi H.W., Jaggi M., Jutila A., Kaleschke L., Katlein C., , Krampe D., Kristensen S.S., Krumpen T., Kurtz N., , Lange B.A., Lei R., Light B., Linhardt F., Liston G.E., , Macfarlane A.R., Mahmud M., Matero I.O., Maus S., , Naderpour R., Nandan V., Niubom A., Oggier M., Oppelt N., Pätzold F., Perron C., Petrovsky T., Pirazzini R., Polashenski C., , Raphael I.A., Regnery J., Rex M., Ricker R., Riemann-Campe K., Rinke A., Rohde J., Salganik E., Scharien R.K., Schiller M., , Semmling M., Shimanchuk E., Shupe M.D., Smith M.M., , Sokolov V., Stanton T., Stroeve J., Thielke L., , Tonboe R.T., Tavri A., Tsamados M., Wagner D.N., , Webster M., Wendisch M. (2022)
Elementa: Science of the Anthropocene, 10, 1 DOI: 10.1525/ elementa.2021.000046. (BibTeX: nicolaus.etal.2022a)
Abstract: See
Year-round observations of the physical snow and ice properties and processes that govern the ice pack
evolution and its interaction with the atmosphere and the ocean were conducted during the
Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition of the
research vessel Polarstern in the Arctic Ocean from October 2019 to September 2020. This work was
embedded into the interdisciplinary design of the 5 MOSAiC teams, studying the atmosphere, the sea ice,
the ocean, the ecosystem, and biogeochemical processes.The overall aim of the snow and sea ice observations
during MOSAiC was to characterize the physical properties of the snow and ice cover comprehensively in the
central Arctic over an entire annual cycle. This objective was achieved by detailed observations of physical
properties and of energy and mass balance of snow and ice. By studying snow and sea ice dynamics over nested
spatial scales from centimeters to tens of kilometers, the variability across scales can be considered. On-ice
observations of in situ and remote sensing properties of the different surface types over all seasons will help
to improve numerical process and climate models and to establish and validate novel satellite remote sensing
methods; the linkages to accompanying airborne measurements, satellite observations, and results of
numerical models are discussed. We found large spatial variabilities of snow metamorphism and thermal
regimes impacting sea ice growth. We conclude that the highly variable snow cover needs to be considered
in more detail (in observations, remote sensing, and models) to better understand snow-related feedback
processes.The ice pack revealed rapid transformations and motions along the drift in all seasons. The number
of coupled ice–ocean interface processes observed in detail are expected to guide upcoming research with
respect to the changing Arctic sea ice
0 Kb
Olivar M.P., Castellón A., Sabatés A., Sarmiento-Lezcano A., Emelianov M., Bernal A., Yang Y., Proud R., Brierley A.S. (2022)
Frontiers in Marine Science DOI: 10.3389/fmars.2022.1028717. (BibTeX: olivar.etal.2022)
Abstract: See
Mesopelagic fish populations are characterised by high species richness and
abundance, and have been identified as important contributors to the active
carbon fluxes in the open ocean. We report variability in communities of
mesopelagic fish between five zones around the Iberian Peninsula, i.e.
Balears and Alboran in the Mediterranean, and Cadiz, Lisboa and Galicia in
the Atlantic. Day and night samples were collected from 7 layers of the water
column with a midwater trawl fitted with a multisampler. Temperature and
salinity regimes were very different on the Mediterranean and Atlantic sides of
the peninsula, with much higher values through the entire water column in the
Mediterranean, characterized by a strong pycnocline. The highest productivity
was observed off Lisboa, where Chlorophyll a concentrations were two orders
of magnitude higher than in any other zone. Samples from the western
Mediterranean held 22 fish species, while 67 were found in the Atlantic. The
lowest diversity and the highest dominance were observed in Balears, and the
highest diversity in Cadiz zone. In all zones, but particularly in those in the
Mediterranean, mesopelagic populations were dominated by a high number of
small fish with low individual biomasses. The species Benthosema glaciale,
Cyclothone pygmaea and Ceratoscopelus maderensis were common in the
Mediterranean populations, whereas in the Atlantic, Cyclothone microdon/
livida, Valenciennellus tripunctulatus, Ceratoscopelus warmingii and
Benthosema suborbitale were the most common species. Temperature and
salinity (both at surface and in the mesopelagic zone) were the main
environmental factors explaining variability in assemblage composition. A
persistent (day-night) deep scattering layer was observed using the vessel
based echosounder in all zones, and was comprised primarily of the
gonostomatid Cyclothone spp. Night-time echosounder observations of
scattering layers near the surface were observed in Balears, Alboran, Cadiz
and Lisboa, where night surface net collections indicated that Myctophidae,
Stomiidae and Phosichthyidae migration extended to the upper 100 m.
Sternoptychids and the gonostomatid Sigmops elongatus seldom reached
the upper 100 m in their night vertical migrations. Night stratified hauls of 30
m resolution carried out in the epipelagic zone showed that abundances
maxima of migratory fish coincided with the location of the Chlorophyll
a maxima.
Keywords: diversity, bristlemouths, lanternfishes, vertical migration, deep scattering layers
0 Kb
Olmedo E., Turiel A., González-Gambau V., González-Haro C., García- Espriu A., Gabarró C., Portabella M., Corbella I., Martín-Neira M., Arias M., Catany R., Sabia R., Oliva R., Scipal K. (2022)
Scientific Reports, 12, 6279 DOI: 10.1038/s41598-022-10265-1. (BibTeX: olmedo.etal.2022)
Abstract: See
Changes in the Earth’s water cycle can be estimated by analyzing sea surface salinity. This variable reflects the balance between precipitation and evaporation over the ocean, since the upper layers of the ocean are the most sensitive to atmosphere–ocean interactions. In situ measurements lack spatial and temporal synopticity and are typically acquired at few meters below the surface. Satellite measurements, on the contrary, are synoptic, repetitive and acquired at the surface. Here we show that the satellite-derived sea surface salinity measurements evidence an intensification of the water cycle (the freshest waters become fresher and vice-versa) which is not observed at the in-situ near-surface salinity measurements. The largest positive differences between surface and near-surface salinity trends are located over regions characterized by a decrease in the mixed layer depth and the sea surface wind speed, and an increase in sea surface temperature, which is consistent with an increased stratification of the water column due to global warming. These results highlight the crucial importance of using satellites to unveil critical changes on ocean–atmosphere fluxes.
0 Kb
Ortigosa I., Bardaji R., Carbonell A., Carrasco O., Castells-Sanabra M., Figuerola R., Hoareau N., Mateu J., Piera J., Puigdefabregas J., Salvador J., Simon C., Vallès-Casanova I., Pelegrí J.L. (2022)
Journal of Marine Science and Engineering, 10, 591 DOI: 10.3390/jmse100505. (BibTeX: ortigosa.etal.2022)
Abstract: See
Shelf waters near large cities, such as Barcelona, are affected not only by meteorological
episodes but also by anthropogenic influence. Scientists usually use data from on-site coastal platforms to analyze and understand these complex water ecosystems because remote sensing satellites have low spatiotemporal resolution and do not provide reliable data so close to the coast. However, platforms with conventional oceanographic instrumentation are expensive to install and maintain. This study presents the scientific adaptation and initial measurements from a “patí a vela”, which is a very popular unipersonal catamaran in Barcelona. This versatile sailing vessel has been adapted to contain several low-cost sensors and instruments to measure water properties. Here, we describe the setup of a multi-parameter prototype, and then focus on results obtained using a low-cost temperature profiler. First, the temperature data are compared and validated with another conventional oceanographic instrument used in monthly oceanographic cruises. Then, field measurements between July and November 2021 are used to explore the relationship between air and water temperature in the Barcelona coastal area, showing the seasonal evolution of the temperature profile. We conclude that citizen sampling from fully sustainable sailing boats may turn into an effective strategy to monitor the urban coastal waters.
Keywords: scientific sailing boat; low-cost sensors; temperature-depth profiler; citizen science
0 Kb
Ostrovskii A.G., Emelianov M.V., Kochetov O.Y., Kremenetskiy V.V., Shvoev D.A., Volkov S.V., Zatsepin A.G., Korovchinsky N.M., Olshanskiy V.M., Olchev A.V. (2022)
Journal of Marine Science and Engineering, 10, 322 DOI: 10.3390/jmse10030322. (BibTeX: ostrovskii.etal.2022)
Abstract: See
Biogeochemical cycles of carbon transformation throughout the euphotic zone of the sea are controlled by physical processes, e.g., daily thermocline, variation in solar irradiance, thermohaline convection, and intermittent mixing. These processes should be regularly observed with sufficient time resolution at fixed geographical locations. This study provides a brief overview of the carbon observational site in the Northeastern Black Sea. The focus is on the design of a new tethered profiler Winchi for the inner continental shelf part of the site. The profiler hull and two outriggers comprise an open trimaran platform that is positively buoyant and tends to maintain a horizontal position in the water. The lower end of the winch wire is secured to the bottom anchor. By unwinding/winding the wire, the profiler ascends/descends while measuring the depth profiles of marine environment parameters ranging from the seafloor to air–sea interface. After surfacing, the profiler determines its location using the Global Positioning System (GPS) and transmits data to (and from) a server on land through the Global System for Mobile Communications (GSM). Initial field tests with the Winchi profiler at the Northeastern Black Sea shelf exhibited promising results. We report these early tests to demonstrate the use of Winchi.
Keywords: greenhouse gases; carbon flux; tethered profiler; winch; real-time data transmission; Black Sea
0 Kb
Polverari F., Portabella M., Lin W., Saap J.W., Stoffelen A., Jelenak Z., Chang P.S. (2022)
IEEE Transactions on Geoscience and Remote Sensing, 60 DOI: 10.1109/TGRS.2021.3079898. (BibTeX: polverari.etal.2022)
Abstract: See
Accurate high and extreme sea surface wind
observations are essential for the meteorological, ocean, and
climate applications. To properly assess and calibrate the current
and future satellite-derived extreme winds, including those from
the C-band scatterometers, building a consolidated high and
extreme wind reference data set is crucial. In this work, a new
approach is presented to assess the consistency between moored
buoys and stepped-frequency microwave radiometer (SFMR)-
derived winds. To overcome the absence of abundant direct collocations between these two data sets, the reprocessed Advanced
Scatterometer (ASCAT)-A winds at the 12.5-km resolution, from
2009 to 2017, have been used to perform an indirect SFMR/buoy
winds’ intercomparison. The ASCAT/SFMR analysis reveals
an ASCAT wind underestimation for winds of above 15 m/s.
SFMR measurements are calibrated using GPS drop-wind-sondes
(dropsondes) data and averaged along-track to represent ASCAT
spatially. On the other hand, ASCAT and buoy winds are in
good agreement up to 25 m/s. The buoy high-wind quality has
been confirmed using a triple collocation approach. Comparing
these results, both SFMR and buoy winds appear to be highly
correlated with ASCAT at the high-wind regime; however, they
show a very different wind speed scaling. An SFMR-based
recalibration of ASCAT winds is proposed, the so-called ASCAT
dropsonde-scale winds, for use by the extreme wind operational
community. However, further work is required to reconcile
dropsonde (thus, SFMR) and buoy wind measurements under
extreme wind conditions
Keywords: High and extreme wind speeds, microwave radiometry, ocean wind reference, spaceborne scatterometry
0 Kb
Polverari F., Sapp J.W., Portabella M., Stoffelen A., Jelenak Z., Chang P.S. (2022)
IEEE Transactions on Geoscience and Remote Sensing, 60 DOI: 10.1109/TGRS.2022.3189310. (BibTeX: polverari.etal.2022a)
Abstract: See
The airborne Stepped Frequency Microwave
Radiometer (SFMR) provides measurements of 10-m ocean-
surface wind speed in high and extreme wind conditions. These
winds are calibrated using the surface-adjusted wind estimates
from the so-called dropsondes. The surface-adjusted winds are
obtained from layer-averaged winds scaled to 10-m altitude to
eliminate the local surface variability not associated with the storm
strength. The SFMR measurements and, consequently, the
surface-adjusted dropsonde winds represent a possible reference
for satellite instrument and model calibration/validation at high
and extreme wind conditions. To this end, representativeness
errors that those measurements may introduce need to be taken
into account to ensure that the storm variability is correctly
resolved in satellite retrievals and modelling. In this work, we
compare the SFMR winds with the dropsonde surface-adjusted
winds derived from the so-called WL150 algorithm, which uses the
lowest 150-meter layer between 10 m to 350 m. We use nine years
of data from 2009 to 2017. We focus on the effects of the layer
altitude and thickness. Our analysis shows that the layer altitude
has a significant impact on dropsonde/SFMR wind comparisons.
Moreover, the averaged winds obtained from layers thinner than
the nominal 150 m and closer to the surface are more
representative of the SFMR surface wind speed than the WL150
speeds. We also find that the surface-adjusted winds are more
representative of 10-km horizontally averaged SFMR winds. We
conclude that for calibration/validation purposes, the WL150
algorithm can introduce noise and the use of actual 10-m
dropsonde measurements should be further investigated.
Keywords: Calibration, dropsondes, ocean surface high and extreme wind reference, tropical cyclones, microwave radiometry
0 Kb
Portal G., Vall-llosera M., Piles M., Jagdhuber T., Camps A., Pablos M., López-Martínez C., Das N.N., Entekhabi D. (2022)
IEEE Transactions on Geoscience and Remote Sensing, 60, 1, 18. DOI: 10.1109/TGRS.2022.3187467. (BibTeX: portal.etal.2022)
Abstract: See
Incidence angle diversity of space-borne radiometer1
and radar systems operating at low microwave frequencies needs2
to be taken into consideration to accurately estimate soil mois-3
ture (SM) across spatial scales. In this study, the single channel4
algorithm (SCA) is first applied to Soil Moisture and Ocean5
Salinity (SMOS) brightness temperatures at vertical polarization6
(TBV ) to estimate SM at coarse resolution (25 km) and develop a7
land cover-specific and incidence angle (32.5◦ , 42.5◦, and 52.5◦ )-8
adaptive calibration of single scattering albedo (ω) and soil9
roughness (h s ) parameters. These effective parameters are used10
together with fine-scale multiangular Sentinel-1 backscatter in a11
single-pass active–passive downscaling approach to estimate TBV12
at fine scale (1 km) for each SMOS incidence angle. These TBV s13
are finally inverted to obtain the corresponding high-resolution14
SM maps. Results over the Iberian Peninsula for year 2018 show15
an increasing trend of ω and a decreasing trend of h s with16
SMOS incidence angle, with almost no variability of ω across17
land cover types. The active–passive covariation parameter is18
shown to increase with SMOS incidence angle and decrease with19
Sentinel-1 incidence angle. Coarse and fine TBV maps from the20
three SMOS incidence angles show similar distributions (mean differences below 0.38 K). Resulting high-resolution SM maps 22
have maximum differences in mean and standard deviation of 23
0.016 and 0.015 m3 /m3 , respectively, and compare well with 24
in situ measurements. Our results indicate that model-based 25
microwave approaches to estimate SM can be adequately adapted 26
to account for the incidence angle diversity of planned missions, 27
such as Copernicus Microwave Imaging Radiometer (CIMR), 28
Radar Observing System for Europe in L-band (ROSE-L), and 29
Sentinel-1 next generation.
Keywords: Active–passive microwave, incidence angle, radiometry, signal covariation, spatial disaggregation.
0 Kb
Salvador X., Fernández-Vilert R., Moles J. (2022)
Journal of Natural history, 56, 5-8, 265-310. DOI: 10.1080/00222933.2022.2040630. (BibTeX: salvador.etal.2022)
Abstract: See
Citizen (or community) science has provided copious and valuable information about charismatic marine taxa such as heterobranch gastropods, thus contributing enormously to the known geographic distribution of many sea slug species. This study reports new records of elusive sea slugs in the coastal western Mediterranean (especially on the Catalan and French Mediterranean coasts) and contributes to new ecological information regarding their phenology, diet and behaviour. Out of 39 species reported here, 23 are new records for the Catalan coast (NE Spain), three are new records of pelagic pteropods for the Spanish Iberian coast, and eight are new records for the French Mediterranean coast. With 25 species found active at night, this study highlights the importance of sampling at night and in shallow, often under-sampled waters with high species diversity. Shallow waters usually have less diving activity and are harder to survey with heavy scuba equipment. We believe that the high-quality photos herein and the related species information will enable researchers, divers and the community to find and recognise these rare species in the Mediterranean basin.
Keywords: marine heterobranchs; new records; uncommon species; Mediterranean Sea; byodiversity
0 Kb
Umbert M., Hoareau N., Salat J., Salvador J., Guimbard S., Olmedo E., Gabarró C. (2022)
Journal of Marine Science and Engineering, 10, 8 DOI: 10.3390/jmse10081078. (BibTeX: umbert.etal.2022b)
Abstract: See
The Vendée Globe is the world’s most famous solo, non-stop, unassisted sailing race. The Institute of Marine Sciences and the Barcelona Ocean Sailing Foundation installed a MicroCAT on the One Ocean One Planet boat. The skipper, Dídac Costa, completed the round trip in 97 days, from 8 November 2020 to 13 February 2021, providing one measurement of temperature and conductivity every 30 s during navigation. More than half of the ship’s route was in the sub-Antarctic zone, between the tropical and polar fronts, and it passed through areas of oceanographic interest such as Southern Patagonia (affected by glacier melting), the Brazil–Malvinas confluence, the Southern Pacific Ocean, and the entire Southern Indian Ocean. This sailing race gave a rare opportunity to measure in-situ sea surface salinity in a region where satellite salinity measurements are not reliable. Due to the decreased sensitivity of brightness temperature to salinity in cold seas, retrieving sea surface salinity at high latitudes remains a major challenge. This paper describes how the data are processed and uses the data to validate satellite salinity products in the sub-Antarctic zone. The sailing race measurements represent surface information (60 cm depth) not available from drifters or Argo floats. Acquiring measurements using round-the-world sailing races would allow us to analyse the evolution of ocean salinity and the impact of changes in the ice extent around Antarctica.
Keywords: sea surface temperature; sea surface salinity; ocean circumnavigation; ships of opportunity; SMOS validation; sub-Antarctic zone
0 Kb
Vázquez A.J., Elosegui P., Lonsdale C.J., Crew G.B., Fish V.L., Ruszczyk C.A. (2022)
Publications of the Astronomical Society of the Pacific, 134, 1040, 12pp. DOI: https://doi.org/10.1088/1538-3873/ac8dc2. (BibTeX: vazquez.etal.2022)
Abstract: See
Correlation for radio interferometer array applications, including Very Long Baseline Interferometry (VLBI), is a multidisciplinary field that traditionally involves astronomy, geodesy, signal processing, and electronic design. In recent years, however, high-performance computing has been taking over electronic design, complicating this mix with the addition of network engineering, parallel programming, and resource scheduling, among others. High- performance applications go a step further by using specialized hardware like Graphics Processing Units (GPUs) or Field Programmable Gate Arrays (FPGAs), challenging engineers to build and maintain high-performance correlators that efficiently use the available resources. Existing literature has generally benchmarked correlators through narrow comparisons on specific scenarios, and the lack of a formal performance characterization prevents a systematic comparison. This combination of ongoing increasing complexity in software correlation together with the lack of performance models in the literature motivates the development of a performance model that allows us not only to characterize existing correlators and predict their performance in different scenarios but, more importantly, to provide an understanding of the trade-offs inherent to the decisions associated with their design. In this paper, we present a model that achieves both objectives. We validate this model against benchmarking results in the literature, and provide an example for its application for improving cost-effectiveness in the usage of cloud resources.
0 Kb
Viudez A. (2022)
Journal of Fluid Mechanics, 949, A-13 DOI: 10.1017/jfm.2022.754. (BibTeX: viudez.2022a)
Abstract: See
Exact solutions of the time-dependent three-dimensional nonlinear vorticity equation for
Euler flows with spherical geometry are provided. The velocity solution is the sum of a
multipolar oscillatory function and a rigid cylindrical motion with swirl. The multipolar
oscillation is a velocity mode whose radial and angular dependencies are given by
the spherical Bessel functions and vector spherical harmonics, respectively. The local
frequency of the velocity oscillations equals the angular speed of the rigid flow times the
angular azimuthal wavenumber of the oscillating flow. The unsteady motion corresponds
to inertial oscillations in multipolar flows with spatial azimuthal waves (non-vanishing
azimuthal wavenumber) in the presence of a background flow with constant axial vorticity.
In these nonlinear solutions, the curl of the Lamb vector has a linear dependence with the
oscillation velocity, a property that makes it possible for the oscillating motion to satisfy
different linear wave equations. Based on these inviscid time-dependent velocity modes,
new exact solutions to the time-dependent Navier–Stokes equation are also provided.
Keywords: waves in rotating fluids, Navier–Stokes equations, vortex dynamics
0 Kb
Viúdez A. (2022)
Journal of Fluid Mechanics, 936, A13 DOI: 10.1017/jfm.2022.73. (BibTeX: viudez.2022)
Abstract: See
Multipolar spherical solutions to the three-dimensional steady vorticity equation are
provided. These solutions are based on the separation of radial and angular contributions
in terms of the spherical Bessel functions and vector spherical harmonics, respectively. In
this set of multipolar vortex solutions, the Hicks–Moffatt swirling vortex is categorized
as a vortex of degree l = 1 and therefore as a vortex dipole. This swirling vortex is
the three-dimensional dipole in spherical geometry equivalent to the two-dimensional
Lamb–Chaplygin dipole in polar geometry. The three-dimensional dipole solution admits
two linearly superposable solutions. The first one is a Trkalian flow and the second one is a
cylindrical solid-body rotation with swirl. The higher l > 1 multipolar vortices found are
either vanishing-helicity vortices or Trkalian flow vortices. The multipolar Trkalian flows
admit two circular polarizations given by the sign of the wavenumber k. It is also found
that piecewise vortex solutions, consisting of interior rotational and exterior potential flow
domains, satisfying velocity continuity conditions at the vortex boundary, are possible in
the general multipolar Trkalian spherical vortex. A particular polarized dipole solution
in three-dimensional cylindrical geometry, consisting as well in the superposition of a
Trkalian flow and a rigid motion, is also analysed. This swirling vortex may be interpreted
as the three-dimensional dipole in cylindrical geometry equivalent to the two-dimensional
Lamb–Chaplygin dipole in polar geometry.
Keywords: vortex flows
0 Kb
Viúdez A. (2022)
European Journal of Mechanics B/Fluids, 98, 247-252. DOI: 10.1016/j.euromechflu.2022.12.011. (BibTeX: viudez.2022b)
Abstract: See
It is shown that a superposition of an arbitrary number of multipolar spherical and cylindrical oscillations in a cylindrical rigid flow with swirl is an exact solution to the time-dependent nonlinear vorticity equation. The oscillations are normal modes whose fundamental frequency and radial wavenumber are given by the angular speed and scaled inverse pitch, respectively, of the rigid flow.
Keywords: exact solucions, vortex flows, waves in swirling flow
0 Kb
Wang S., Yang X., Portabella M., Yuen K.V., Zhang M., Du Y. (2022)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 15, 8806-8818. DOI: 10.1109/JSTARS.2022.3213822. (BibTeX: wang.etal.2022)
Abstract: See
The tangential wind speed increases from the center
to the eyewall of tropical cyclones (TC) along the radial direction
and begins to decay when it extends outward. The tangential wind
profile model is one of the most effective and widely used methods
to reconstruct the TC radial wind speed. This article proposes a
parametric tangential wind profile (TWP) model based on high-
spatial-resolution synthetic aperture radar (SAR) imagery. The
new model functions are piecewise with maximum tangential wind
speed as a threshold, and all of them are designed as nonlinear.
Notably, the derivative at the segmentation threshold is zero to
ensure a smooth transition of the estimated wind speed profile. With
the SAR-derived azimuth-averaged wind speed, we can determine
the model parameters and get the tangential wind speed. The TWP
model outperforms the commonly used single-modified Rankine
vortex (SMRV) model, as it better resolves the tangential wind
profile shape as depicted by both SAR-derived winds and hurricane
hunter stepped-frequency microwave radiometer derived winds. A
comprehensive analysis of the TWP model parameters is carried
out by fitting tangential winds for 620 hurricane hunter flights.
Interestingly, the tangential wind profiles for major hurricanes
show a similar shape. The proposed TWP model can be used for
improved TC characterization and forecasting purposes
Keywords: Parametric modeling, synthetic aperture radar (SAR), Tangential wind speed, tropical cyclone (TC)
0 Kb
Woods S.M., Daskolia M., Joly A., Bonnet P., Soacha K., Liñán S., Woods T., Piera J., Ceccaroni L. (2022)
Sustainability, 14, 4078 DOI: 10.3390/su14074078. (BibTeX: woods.etal.2022)
Abstract: See
There is a growing acknowledgement that citizen observatories, and other forms of citizen-
generated data, have a significant role in tracking progress towards the Sustainable Development Goals. This is evident in the increasing number of Sustainable Development Goals’ indicators for which such data are already being used and in the high-level recognition of the potential role that citizen science can play. In this article, we argue that networks of citizen observatories will help realise this potential. Drawing on the Cos4Cloud project as an example, we highlight how such networks can make citizen-generated data more interoperable and accessible (among other qualities), increasing their impact and usefulness. Furthermore, we highlight other, perhaps overlooked, advantages of citizen observatories and citizen-generated data: educating and informing citizen scientists about the Sustainable Development Goals and co-creating solutions to the global challenges they addres
Keywords: citizen science; citizen observatory; Sustainable Development Goals; interoperability; co-design; education
0 Kb
Zhao X., Lin W., Portabella M., Wang Z., He Y. (2022)
Remote Sensing of Environment, 274, 113015 DOI: 10.1016/j.rse.2022.113015. (BibTeX: zhao.etal.2022)
Abstract: See
The Ku-band scatterometer onboard China France Oceanography Satellite (CFOSAT) observes the sea surface with two conically scanning fan beams. Compared to the prior Ku-band pencil beam scatterometers, this innovative observing mechanism provides more independent backscatter measurements at varying incidence and azimuth angles, as such it brings challenges for the sea surface wind inversion, particularly under rainy conditions. In this paper, the rain effects on the CFOSAT SCATterometer (CSCAT) are investigated using the collocated numerical weather prediction (NWP) wind data and the Global Precipitation Measurement (GPM) microwave imager (GMI) rain data. Similar to the prior Ku-band or C-band scatterometers, the sensitivity of CSCAT radar backscatter to rain substantially varies with wind speed, radar polarization and incidence angle. However, due to the complex observation geometries, rain effects on the CSCAT retrieved winds is more complex than that of prior scatterometers, which may lead to a remarkable underestimation of CSCAT wind speed at high winds and heavy rain conditions. A simple simulation method is used to clarify the relation between the retrieved wind speed and the dependency of radar rain effects on the incidence angle. It is found that the backscatter measurements at low incidence angles, which are generally underestimated at high winds and heavy rainy conditions, have a larger influence on the wind inversion minimization, leading to much lower retrieved wind speeds than those of ECMWF and the pencil beam scatterometer (e.g., Haiyang-2B scattometer). Under low and moderate rain conditions though, a more compensated effect between low and high incidence angle measurements is found, leading to generally unbiased CSCAT high winds, in contrast to the generally underestimated pencil-beam scatterometer winds.
Keywords: CFOSAT Scatterometer Backscatter Rain effects Wind quality
0 Kb
Zibordi G., Talone M., Mélin F. (2022)
IEEE Geoscience and Remote Sensing Letters, 19, 1502905, 1-5. DOI: 10.1109/LGRS.2021.3134876. (BibTeX: zibordi.etal.2022)
Abstract: See
The quantification of uncertainties affecting satellite ocean color products is a fundamental step to ensure their compliance with mission and science requirements. This work investigated a methodology relying on the use of in situ radiometric data with known uncertainties to determine those affecting matching satellite data. By exploiting in situ radiometric data from the Ocean Color component of the Aerosol Robotic Network (AERONET-OC), an advanced method was applied to radiometric data products from the Ocean and Land Color Instruments onboard the Sentinel-3A satellite (OLCI-A) and the
Visible Infrared Imager Radiometer Suite onboard the Suomi
National-Polar Orbiting Partnership satellite (VIIRS-S). The
results from the analysis support the relevance of the method
proposed.
Keywords: Ocean color, remote sensing, uncertainties
0 Kb
Zibordi G., Kwiatkowska E., Mélin F., Talone M., Cazzaniga I., Dessailly D., Gossn J.I. (2022)
Remote Sensing of Environment, 272, 112911. DOI: 10.1016/j.rse.2022.112911. (BibTeX: zibordi.etal.2022a)
Abstract: See
The Ocean and Land Color Instruments (OLCI) operated onboard the Copernicus Sentinel-3 satellites are providing globally distributed Ocean Color Radiometry (OCR) data products of relevance for environmental and climate applications. This work summarizes results on the assessment of fundamental OCR data from the Operational Baseline 3 Collection OL_L2M.003.01 of OLCI-A and OLCI-B onboard Sentinel-3A and Sentinel-3B, respectively. Evaluated products are the satellite derived normalized water-leaving radiance LWN(λ), aerosol optical depth at 865 nm τa(865) and Ångstrom ¨ exponent α determined in the near-infrared spectral region. The analyses were performed relying on in situ reference data from the Ocean Color component of the Aerosol Robotic Network (AERONET-OC) from sites representative of diverse water types. The comparison of OLCI-A and OLCI-B with AERONET-OC LWN(λ) for oligotrophic/mesotrophic waters shows cross-mission consistent spectral median percent differences (i.e., biases) varying within ±6% at the blue-green center-wavelengths. The analysis of data from regions characterized by optically complex waters, however, displays systematic negative biases for both OLCI-A and OLCI-B further increasing for waters dominated by chromophoric dissolved organic matter, thus suggesting a dependence of the atmospheric correction on water type. The direct inter-comparison of OLCI-B and OLCI-A LWN(λ) from the Tandem Phase characterized by Sentinel-3B and Sentinel-3A flying 30 s apart on the same orbit, shows spectral median percent differences lower than ±1% in the 412–560 nm interval, of approximately +5% at 620 and 665 nm, and − 7% at 400 nm. However, outside the Tandem Phase, the intercomparison of OLCI-B and OLCI-A data products indicates large and systematic differences explained by a notable dependence on the viewing angle. The evaluation of τa(865) and α across different geographic regions exhibits overestimated values between +48 and + 79% for the former and underestimated values between − 28% and − 41% for the latter. A complementary evaluation of OCR data products from the Visible Infrared Imager Radiometer Suite on board the Suomi National Polar-orbiting Partnership (VIIRS-S), proposed as a further indirect term of reference for OLCI-A and OLCI-B data, shows large underestimates of LWN(λ) with respect to the in situ reference data in the various water types at 410 nm. Nevertheless, opposite to OLCI-A and OLCI-B data products, absolute differences between VIIRS-S and in situ reference data do not reveal any large or systematic dependence on water type and satellite viewing angle. Overall results suggest the need for further developing the OLCI-A and OLCI-B atmospheric correction, possibly improving the capability to identify aerosol types and to model scattering processes.
