Articles

Els filtres actuals son: Any inici = 2021, Any final = 2022
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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)
Resum: Veure
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.
Paraules clau: HPLC CHEMTAX Spring bloom Synechococcus bloom Ecological preferences Size distribution
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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)
Resum: Veure
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.
Paraules clau: Ocean color, remote sensing, uncertainties
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Boutin J., Reul N., Koehler J., Martin A., Catany R., Guimbard S., Rouffi F., Vergely J.L., Arias M., Chakroun M., Corato G., Estella-Perez V., Hasson A., Josey S., Khvorostyanov D., , Mignot J., Olivier L., Reverdin G., Stammer D., Supply A., Thouvenin-Masson C., Turiel A., Vialard J., Cipollini P., Donlon C., Sabia R., Mecklenburg S. (2021)
Journal of Geophysical Research: Oceans, 126, 11 DOI: 10.1029/2021JC017676. (BibTeX: boutin.etal.2021)
Resum: Veure
Sea Surface Salinity (SSS) is an increasingly used Essential Ocean and Climate Variable. The Soil Moisture and Ocean Salinity (SMOS), Aquarius, and Soil Moisture Active Passive (SMAP) satellite missions all provide SSS measurements, with very different instrumental features leading to specific measurement characteristics. The Climate Change Initiative Salinity project (CCI + SSS) aims to produce a SSS Climate Data Record (CDR) that addresses well-established user needs based on those satellite measurements. To generate a homogeneous CDR, instrumental differences are carefully adjusted based on in-depth analysis of the measurements themselves, together with some limited use of independent reference data. An optimal interpolation in the time domain without temporal relaxation to reference data or spatial smoothing is applied. This allows preserving the original datasets variability. SSS CCI fields are well suited for monitoring weekly to interannual signals, at spatial scales ranging from 50 km to the basin scale. They display large year-to-year seasonal variations over the 2010–2019 decade, sometimes by more than ±0.4 over large regions. The robust standard deviation of the monthly CCI SSS minus in situ Argo salinities is 0.15 globally, while it is at least 0.20 with individual satellite SSS fields. r2 is 0.97, similar or better than with original datasets. The correlation with independent ship thermosalinographs SSS further highlights the CCI data set excellent performance, especially near land areas. During the SMOS-Aquarius period, when the representativity uncertainties are the largest, r2 is 0.84 with CCI while it is 0.48 with the Aquarius original data set. SSS CCI data are freely available and will be updated and extended as more satellite data become available
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Cazzaniga I., Zibordi G., Mélin F., Kwiatkowska E., Talone M., Dessailly D., Gossn J.I., Müller D. (2021)
IEEE Geoscience and Remote Sensing Letters DOI: 10.1109/LGRS.2021.3136291. (BibTeX: cazzaniga.etal.2021)
Resum: Veure
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.
Paraules clau: Remote Sensing, Ocean Color, Validation
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Herbert C., Munoz-Martin J.F., Llaveria D., Pablos M., Camps A. (2021)
Remote Sensing, 13, 1366. DOI: 10.3390/rs13071366. (BibTeX: herbert.etal.2021)
Resum: Veure
Several methods have been developed to provide polar maps of sea ice thickness (SIT) from L-band brightness temperature (TB) and altimetry data. Current process-based inversion methods to yield SIT fail to address the complex surface characteristics because sea ice is subject to strong seasonal dynamics and ice-physical properties are often non-linearly related. Neural networks can be trained to find hidden links among large datasets and often perform better on convoluted problems for which traditional approaches miss out important relationships between the observations. The FSSCat mission launched on 3 September 2020, carries the Flexible Microwave Payload-2 (FMPL-2), which contains the first Reflected Global Navigation Satellite System (GNSS-R) and L-band radiometer on board a CubeSat—designed to provide TB data on global coverage for soil moisture retrieval, and sea ice applications. This work investigates a predictive regression neural network approach with the goal to infer SIT using FMPL-2 TB and ancillary data (sea ice concentration, surface temperature, and sea ice freeboard). Two models—covering thin ice up to 0.6 m and full-range thickness—were separately trained on Arctic data in a two-month period from mid-October to the beginning of December 2020, while using ground truth data derived from the Soil Moisture and Ocean Salinity (SMOS) and Cryosat-2 missions. The thin ice and the full-range models resulted in a mean absolute error of 6.5 cm and 23 cm, respectively. Both of the models allowed for one to produce weekly composites of Arctic maps, and monthly composites of Antarctic SIT were predicted based on the Arctic full-range model. This work presents the first results of the FSSCat mission over the polar regions. It reveals the benefits of neural networks for sea ice retrievals and demonstrates that moderate-cost CubeSat missions can provide valuable data for applications in Earth observation.
Paraules clau: predictive regression neural networks, sea ice thickness, microwave radiometry, CubeSats
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Hernández-Morales D.P., Romaña-Torres Y., Jaramillo-Vélez A., Pelegrí J.L., Toro V.G. (2021)
Bulletin of Marine and Coastal Research, 50, 2, 9-30. DOI: 10.25268/bimc.invemar.2021.50.2.993. (BibTeX: hernandezmorales.etal.2021)
Resum: Veure
Good knowledge of the coastal circulation patterns is essential for a proper management of the coastline, especially in areas with a high anthropic pressure. In order to determine the main characteristics of the coastal currents in the Gulf of Urabá, the seasonal patterns of surface circulation were measured and analyzed during times of high and low rainfall along 6 km of coastline, between the Punta de Las Vacas and Punta Yarumal coastal spit systems, in the municipality of Turbo, Antioquia. These measurements were made with surface drifters, which were launched at different tide stages and tracked for time periods based on the semi-diurnal cycle. The in-situ measurements were analyzed alongside tide and wind data from a climatic station located near the gulf. The circulation patterns behaved differently depending on the season of the year. In the rainy season, with southerly winds, the drifters moved mainly towards the north while during the dry season, with northerly winds, all the drifters moved to the south. Although the circulation patterns showed a strong relationship with the tidal cycle and wind conditions, the Turbo and El Uno Bays modified some of the drifter’s paths.
Paraules clau: surface circulation, wind, tide, drifters, coastal currents
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Isern-Fontanet J., García-Ladona E., González-Haro C., Turiel A., Rosell-Fieschi M., Company J.B., Padial A. (2021)
Remote Sensing, 13, 3635 DOI: 10.3390/rs13183635. (BibTeX: isernfontanet.etal.2021)
Resum: Veure
Current observations of ocean currents are mainly based on altimetric measurements of Sea Surface Heights (SSH), however the characteristics of the present-day constellation of altimeters are only capable to retrieve surface currents at scales larger than 50–70 km. By contrast, infrared and visible radiometers reach spatial resolutions thirty times higher than altimeters under cloud-free conditions. During the last years, it has been shown how the Surface Quasi-Geostrophic (SQG) approximation is able to reconstruct surface currents from measured Sea Surface Temperature (SST), but it has not been yet used to retrieve velocities at scales shorter than those provided by altimeters. In this study, the velocity field of ocean structures with characteristic lengths between 10 and 20 km has been derived from infrared SST using the SQG approach and compared to the velocities derived from the trajectories of Lagrangian drifters. Results show that the SQG approach is able to reconstruct the direction of the velocity field with observed RMS errors between 8 and 15 degrees and linear correlations between 0.85 and 0.99. The reconstruction of the modulus of the velocity is more problematic due to two limitations of the SQG approach: the need to calibrate the level of energy and the ageostrophic contributions. If drifter trajectories are used to calibrate velocities and the analysis is restricted to small Rossby numbers, the RMS error in the range of 10 to 16 cm/s and linear correlations can be as high as 0.97.
Paraules clau: sea surface temperature; quasi-geostrophic equations; mesoscale and submesoscale dynamics; ocean velocity determination; mediterranean sea
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Isern-Fontanet J., Turiel A. (2021)
Journal of Physical Oceanography, 51, 8, 2639-2653. DOI: 10.1175/JPO-D-20-0256.1. (BibTeX: isernfontanet.turiel.2021)
Resum: Veure
The multifractal theory of turbulence is used to investigate the energy cascade in the northwestern Atlantic Ocean. The statistics of singularity exponents of horizontal velocity gradients computed from in situ measurements at 2-km resolution are used to characterize the anomalous scaling of the velocity structure functions at depths between 50 and 500 m. Here, we show that the degree of anomalous scaling can be quantified using singularity exponents. Observations reveal, on one side, that the anomalous scaling has a linear dependence on the exponent characterizing the strongest velocity gradient and, on the other side, that the slope of this linear dependence decreases with depth. Since the observed distribution of exponents is asymmetric about the mode at all depths, we use an infinitely divisible asymmetric model of the energy cascade, the log–Poisson model, to derive the functional dependence of the anomalous scaling with the exponent of the strongest velocity gradient, as well as the dependence with dissipation. Using this model we can interpret the vertical change of the linear slope between the anomalous scaling and the exponents of the strongest velocity gradients as a change in the energy cascade. This interpretation assumes the validity of the multifractal theory of turbulence, which has been assessed in previous studies.
Paraules clau: Atlantic Ocean; Mesoscale processes; Turbulence; In situ oceanic observations
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Llaveria D., Munoz-Martin J.F., Herbet C., Pablos M., Park H., Camps A. (2021)
Remote Sensing, 13, 1139. DOI: 10.3390/rs13061139. (BibTeX: llaveria.etal.2021)
Resum: Veure
CubeSat-based Earth Observation missions have emerged in recent times, achievingscientifically valuable data at a moderate cost. FSSCat is a two 6U CubeSats mission, winner ofthe ESA S3challenge and overall winner of the 2017 Copernicus Masters Competition, that waslaunched in September 2020. The first satellite,3Cat-5/A, carries the FMPL-2 instrument, an L-bandmicrowave radiometer and a GNSS-Reflectometer. This work presents a neural network approachfor retrieving sea ice concentration and sea ice extent maps on the Arctic and the Antarctic oceansusing FMPL-2 data. The results from the first months of operations are presented and analyzed,and the quality of the retrieved maps is assessed by comparing them with other existing sea iceconcentration maps. As compared to OSI SAF products, the overall accuracy for the sea ice extentmaps is greater than 97% using MWR data, and up to 99% when using combined GNSS-R and MWRdata. In the case of Sea ice concentration, the absolute errors are lower than 5%, with MWR and lowerthan 3% combining it with the GNSS-R. The total extent area computed using this methodology isclose, with 2.5% difference, to those computed by other well consolidated algorithms, such as OSISAF or NSIDC. The approach presented for estimating sea ice extent and concentration maps is acost-effective alternative, and using a constellation of CubeSats, it can be further improved
Paraules clau: sea ice, microwave radiometry, GNSS-R; nanosatellite, earth observation, neural networs
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Medina-Lopez E., McMillan D., Lazic J., Hart E., Zen S., Angeloudis A., Bannon E., Browell J., Dorling S., Dorrell R.M., Forster R., Old C., Payne G.S., Porter G., Rabaneda A.S., Sellar B., Tapoglou E., Trifonova N., Woodhouse I.H., Zampollo A. (2021)
Remote Sensing of Environment, 264, 112588 DOI: 10.1016/j.rse.2021.112588. (BibTeX: medinalopez.etal.2021)
Resum: Veure
Can satellite data be used to address challenges currently faced by the Offshore Renewable Energy (ORE) sector? What benefit can satellite observations bring to resource assessment and maintenance of ORE farms? Can satellite observations be used to assess the environmental impact of offshore renewables leading towards a more sustainable ORE sector? This review paper faces these questions presenting a holistic view of the current interactions between satellite and ORE sectors, and future needs to make this partnership grow. The aim of the work is to start the conversation between these sectors by establishing a common ground. We present offshore needs and satellite technology limitations, as well as potential opportunities and areas of growth. To better understand this, the reader is guided through the history, current developments, challenges and future of offshore wind, tidal and wave energy technologies. Then, an overview on satellite observations for ocean applications is given, covering types of instruments and how they are used to provide different metocean variables, satellite performance, and data processing and integration. Past, present and future satellite missions are also discussed. Finally, the paper focuses on innovation opportunities and the potential of synergies between the ORE and satellite sectors. Specifically, we pay attention to improvements that satellite observations could bring to standard measurement techniques: assessing uncertainty, wind, tidal and wave conditions forecast, as well as environmental monitoring from space. Satellite–enabled measurement of ocean physical processes and applications for fisheries, mammals and birds, and habitat change, are also discussed in depth.
Paraules clau: Satellite data, Offshore renewable energy (ORE), Wind, Tidal, Wave, SAR, Sustainable ORE secto
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Munoz-Martin J.F., Onrubia R., Pascual D., Park H., Pablos M., Camps A., Rüdiger C., Walker J., Monerris A. (2021)
Remote Sensing, 13, 4, 797. DOI: 10.3390/rs13040797. (BibTeX: munozmartin.etal.2021)
Resum: Veure
Global Navigation Satellite System—Reflectometry (GNSS-R) has already proven its potential for retrieving a number of geophysical parameters, including soil moisture. However, single-pass GNSS-R soil moisture retrieval is still a challenge. This study presents a comparison of two different data sets acquired with the Microwave Interferometer Reflectometer (MIR), an airborne-based dual-band (L1/E1 and L5/E5a), multiconstellation (GPS and Galileo) GNSS-R instrument with two 19-element antenna arrays with four electronically steered beams each. The instrument was flown twice over the OzNet soil moisture monitoring network in southern New South Wales (Australia): the first flight was performed after a long period without rain, and the second one just after a rain event. In this work, the impact of surface roughness and vegetation attenuation in the reflectivity of the GNSS-R signal is assessed at both L1 and L5 bands. The work analyzes the reflectivity at different integration times, and finally, an artificial neural network is used to retrieve soil moisture from the reflectivity values. The algorithm is trained and compared to a 20-m resolution downscaled soil moisture estimate derived from SMOS soil moisture, Sentinel-2 normalized difference vegetation index (NDVI) data, and ECMWF Land Surface Temperature
Paraules clau: GNSS-R; dual-band; airborne; soil moisture; surface roughness; vegetation
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Munoz-Martin J.F., Llaveria D., Herbert C., Pablos M., Park H., Camps A. (2021)
Remote Sensing, 13, 5, 994. DOI: 10.3390/rs13050994. (BibTeX: munozmartin.etal.2021a)
Resum: Veure
The Federated Satellite System mission (FSSCat) was the winner of the 2017 Copernicus Masters Competition and the first Copernicus third-party mission based on CubeSats. One of FSSCat’s objectives is to provide coarse Soil Moisture (SM) estimations by means of passive microwave measurements collected by Flexible Microwave Payload-2 (FMPL-2). This payload is a novel CubeSat based instrument combining an L1/E1 Global Navigation Satellite Systems-Reflectometer (GNSS-R) and an L-band Microwave Radiometer (MWR) using software-defined radio. This work presents the first results over land of the first two months of operations after the commissioning phase, from 1 October to 4 December 2020. Four neural network algorithms are implemented and analyzed in terms of different sets of input features to yield maps of SM content over the Northern Hemisphere (latitudes above 45 ºN). The first algorithm uses the surface skin temperature from the European Centre of Medium-Range Weather Forecast (ECMWF) in conjunction with the 16 day averaged Normalized Difference Vegetation Index (NDVI) from the Moderate Resolution Imaging Spectroradiometer (MODIS) to estimate SM and to use it as a comparison dataset for evaluating the additional models. A second approach is implemented to retrieve SM, which complements the first model using FMPL-2 L-band MWR antenna temperature measurements, showing a better performance than in the first case. The error standard deviation of this model referred to the Soil Moisture and Ocean Salinity (SMOS) SM product gridded at 36 km is 0.074 m3/m3. The third algorithm proposes a new approach to retrieve SM using FMPL-2 GNSS-R data. The mean and standard deviation of the GNSS-R reflectivity are obtained by averaging consecutive observations based on a sliding window and are further included as additional input features to the network. The model output shows an accurate SM estimation compared to a 9 km SMOS SM product, with an error of 0.087 m3/m3. Finally, a fourth model combines MWR and GNSS-R data and outperforms the previous approaches, with an error of just 0.063 m3/m3. These results demonstrate the capabilities of FMPL-2 to provide SM estimates over land with a good agreement with respect to SMOS SM
Paraules clau: GNSS-R; L-band; microwave radiometry; CubeSat; soil moisture
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Niell A.E., Barrett J.P., Cappallo R.J., Corey B.E., Elosegui P., Mondal D., Rajagopalan G., Ruszczyk C.A., Titus M.A. (2021)
Journal of Geodesy, 95, 65 DOI: 10.1007/s00190-021-01505-9. (BibTeX: niell.etal.2021)
Resum: Veure
We measured the components of the 31-m-long vector between the two very-long-baseline interferometry (VLBI) antennas at the Kokee Park Geophysical Observatory (KPGO), Hawaii, with approximately 1 mm precision using phase delay observables from dedicated VLBI observations in 2016 and 2018. The two KPGO antennas are the 20 m legacy VLBI antenna and the 12 m VLBI Global Observing System (VGOS) antenna. Independent estimates of the vector between the two antennas were obtained by the National Geodetic Survey (NGS) using standard optical surveys in 2015 and 2018. The uncertainties of the latter survey were 0.3 and 0.7 mm in the horizontal and vertical components of the baseline, respectively. We applied corrections to the measured positions for the varying thermal deformation of the antennas on the diferent days of the VLBI and survey measurements, which can amount to 1 mm, bringing all results to a common reference temperature. The diference between the VLBI and survey results are 0.2±0.4 mm, −1.3±0.4 mm, and 0.8±0.8 mm in the East, North, and Up topocentric components, respectively. We also estimate that the Up component of the baseline may sufer from systematic errors due to gravitational deformation and uncalibrated instrumental delay variations at the 20 m antenna that may reach ±10 and −2 mm, respectively, resulting in an accuracy uncertainty on the order of 10 mm for the relative heights of the antennas. Furthermore, possible tilting of the 12 m antenna increases the uncertainties in the diferences in the horizontal components to 1.0 mm. These results bring into focus the importance of (1) correcting to a common reference temperature the measurements of the reference points of all geodetic instruments within a site, (2) obtaining measurements of the gravitational deformation of all antennas, and (3) monitoring local motions of the geodetic instruments. These results have signifcant implications for the accuracy of global reference frames that require accurate local ties between geodetic instruments, such as the International Terrestrial Reference Frame (ITRF).
Paraules clau: Geodetic VLBI · Reference Frames · ITRF · Global Geodetic Observing System · Core sites · Local vector ties · Phase delay VLBI · Antenna thermal deformation
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Nunziata F., Li X., Marino A., Shao W., Portabella M., Yang X., Buono A. (2021)
Remote Sensing, 13, 3126 DOI: 10.3390/rs13163126. (BibTeX: nunziata.etal.2021)
Resum: Veure
In this project report, the main outcomes relevant to the Sino-European Dragon-4 cooperation project ID 32235 “Microwave satellite measurements for coastal area and extreme weather monitoring” are reported. The project aimed at strengthening the Sino-European research cooperation in the exploitation of European Space Agency, Chinese and third-party mission Earth Observation (EO) microwave satellite data. The latter were exploited to perform an effective monitoring of coastal areas, even under extreme weather conditions. An integrated multifrequency/polarization approach based on complementary microwave sensors (e.g., Synthetic Aperture Radar, scatterometer, radiometer), together with ancillary information coming from independent sources, i.e., optical imagery, numerical simulations and ground measurements, was designed. In this framework, several tasks were addressed including marine target detection, sea pollution, sea surface wind estimation and coastline extraction/classification. The main outcomes are both theoretical (i.e., new models and algorithms were developed) and applicative (i.e., user-friendly maps were provided to the end-user community of coastal area management according to smart processing of remotely sensed data). The scientific relevance consists in the development of new algorithms, the effectiveness and robustness of which were verified on actual microwave measurements, and the improvement of existing methodologies to deal with challenging test case
Paraules clau: microwave satellites; multipolarization; multifrequency; oceans; coastal areas; coastline; sea wind field; ocean pollution; ships
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Olivé A., Pelegrí J.L., Machín F.J., Vallès-Casanova I. (2021)
Journal of Geophysical Research: Oceans, 126, 7 DOI: 10.1029/2020JC017025. (BibTeX: olive.etal.2021)
Resum: Veure
Southern Ocean waters enter the South Atlantic Ocean through the Scotia Sea along pathways constrained by the bathymetry of the northern Scotia Sea passages. We use the Argo profiling-float data set to calculate the water transports in and out of the region, focusing on the water balances down to the deepest isoneutral sampled in all passages (γn = 28.0 kg m−3, located between about 500 and 2,000 m in the Drake Passage and even shallower in the Northern Passages). Down to this reference level, the water inflow through the Drake Passage is 140.8 ± 7.4 Sv and the water outflow through the deeper portions of the Northern Passages is 115.9 ± 8.3 Sv, implying a leakage of about 25 ± 11.1 Sv over topography shallower than 1,000 m. Below the reference isoneutral and down to 2,000 m, an additional 23.4 Sv enter through the Drake Passage; when added to reported inputs of about 20 Sv through the South Scotia Ridge, this accounts well for the observed 43.4 Sv outflow–from 28.0 kg m−3 to 2,000 m–through the Northern Passages. Relative to the 2,000 m reference level, the mean barotropic contribution always represents over half the total transports. We also observe substantial seasonal and moderate interannual variations in the water transports and composition (peak differences occur seasonally in the Drake Passage, with a range of 111–174 Sv), associated with changes in water exchange across the frontal systems. Two independent measures set the water mean-residence time in the Scotia Sea at about 6–8 months.
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Olivé A., Vinha B., Machín F., Zerbetto F., Bakalis E., Fraile-Nuez E. (2021)
Geosciences, 11, 374 DOI: 10.3390/geosciences11090374. (BibTeX: olive.etal.2021a)
Resum: Veure
Temperature and conductivity fluctuations caused by the hydrothermal emissions released during the degasification stage of the Tagoro submarine volcano (Canary Islands, Spain) have been analysed as a robust proxy for characterising and forecasting the activity of the system. A total of 21 conductivity-temperature-depth time series were gathered on a regular high-resolution grid over the main crater of Tagoro volcano. Temperature and conductivity time series, as manifestations of stochastic events, were investigated in terms of variance and analysed by the Generalised Moments Method (GMM). GMM provides the statistical moments, the structure functions of a process whose shape is an indicator of the underlying stochastic mechanisms and the state of activity of the submarine volcano. Our findings confirm an active hydrothermal process in the submarine volcano with a sub-normal behaviour resulting from anti-persistent fluctuations in time. Its hydrothermal emissions are classified as multifractal processes whose structure functions present a crossover between two time scales. In the shorter time scale, findings point to the multiplicative action of two random processes, hydrothermal vents, which carries those fluctuations driving the circulation over the crater, and the overlying aquatic environment. Given that both temperature and conductivity fluctuations are nonstationary, Tagoro submarine volcano can be characterised as an open system exchanging energy to its surrounding
Paraules clau: Tagoro submarine volcano; time series; volcanic activity; generalised moments method; stochastic processes
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Olmedo E., González-Haro C., Hoareau N., Umbert M., González-Gambau V., Martínez J., Gabarró C., Turiel A. (2021)
Earth System Science Data, 13, 857-888. DOI: 10.5194/essd-13-857-2021. (BibTeX: olmedo.etal.2021)
Resum: Veure
After more than 10 years in orbit, the Soil Moisture and Ocean Salinity (SMOS) European mis-sion is still a unique, high-quality instrument for providing soil moisture over land and sea surface salinity(SSS) over the oceans. At the Barcelona Expert Center (BEC), a new reprocessing of 9 years (2011–2019)of global SMOS SSS maps has been generated. This work presents the algorithms used in the generation ofBEC global SMOS SSS product v2.0, as well as an extensive quality assessment. Three SMOS SSS fields aredistributed: a high-resolution level-3 product (with DOI https://doi.org/10.20350/digitalCSIC/12601, Olmedoet al., 2020a) consisting of binned SSS in 9 d maps at 0.25◦×0.25◦; low-resolution level-3 SSS computedfrom the binned salinity by applying a smoothing spatial window of 50 km radius; and level-4 SSS (with DOIhttps://doi.org/10.20350/digitalCSIC/12600, Olmedo et al., 2020b) consisting of daily 0.05◦×0.05◦maps thatare computed by multifractal fusion with sea surface temperature maps. For the validation of BEC SSS products,we have applied a battery of tests aimed at the assessment of quality of the products both in value and in structure.First, we have compared BEC SSS products with near-to-surface salinity measurements provided by Argo floats.Secondly, we have assessed the geophysical consistency of the products characterized by singularity analysis,and the effective spatial resolutions are also estimated by means of power density spectra and singularity densityspectra. Finally, we have calculated full maps of SSS errors by using correlated triple collocation. We have com-pared the performance of the BEC SMOS product with other satellite SSS and reanalysis products. The mainoutcomes of this quality assessment are as follows. (i) The bias between BEC SMOS and Argo salinity is lowerthan 0.02 psu at a global scale, while the standard deviation of their difference is lower than 0.34 and 0.27 psu forthe high- and low-resolution level-3 fields (respectively) and 0.24 psu for the level-4 salinity. (ii) The effectivespatial resolution is around 40 km for all SSS products and regions. (iii) The results from triple collocation showthe BEC SMOS level-4 product as the product with the lowest estimated salinity error in most of the globalocean and the BEC SMOS high-resolution level-3 as the one with the lowest estimated salinity error in regionsstrongly affected by rainfall and continental freshwater discharge
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Ortigosa I., Castells-Sanabra M., Mateu J., Bardaji R., Hoareau N., Simon C., Pelegrí J.L., Vallès-Casanova I. (2021)
Journal of Maritime Research, 17, 3, 88-94. (BibTeX: ortigosa.etal.2021)
Resum: Veure
This paper presents the first results of the Barcelona Institute of Culture’s grant for research and innovation projects under the 2019 Barcelona Science Plan entitled “Development of a citizen monitoring program for the Barcelona waters: The Scientific Patí a Vela”. The main objective of this project is to develop a small Patí a Vela (PV) fleet that can routinely sample the Barcelona coastal waters and report their observations to an open-access interactive web. The Pat´ı a Vela boat was designed in 1942 by the Monge brothers. It is a lightweight one- person catamaran with a single Marconi sail and no boom. The main objective of this contribution is to adapt the Patí a Vela model attaching an on-board platform with scientific instruments (sensors and devices) and determine the new stability characteristics and seakeeping performance. This will allow an adequate sampling of the Barcelona coast waters and the systematic measurements of the essential physical and biogeochemical variables detecting variations along the coast, hence identifying potential sources of contamination. It will also provide the necessaryknowledge of natural and anthropogenic seasonality.
Paraules clau: Stability; seakeeping, recreational sailing; ocean monitoring, low cost environmental sensors.
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Orué-Echevarría D., Pelegrí J.L., Alonso-González I.J., Benítez-Barrios V.M., Emelianov M., García-Olivares A., Gasser-Rubinat M., De La Fuente P., Herrero C., Isern-Fontanet J., Masdeu-Navarro M., Peña-Izquierdo J., Piola A.R., Ramírez-Garrido S., Rosell-Fieschi M., Salvador J., Saraceno M., Valla D., Vallès-Casanova I., Vidal M. (2021)
Deep-Sea Research. Part I: Oceanographic Research Papers, 172, 103533 DOI: 10.1016/j.dsr.2021.103533. (BibTeX: orueechevarria.etal.2021)
Resum: Veure
The encountering of the subtropical Brazil Current (BC) and the subantarctic Malvinas Current (MC) along the western margin of the Argentine Basin forms the Brazil-Malvinas Confluence (BMC), one of the most intense open-ocean fronts in the world ocean and a site for the formation of intermediate water masses. Here, we provide a comprehensive description of the BMC based on physical and biogeochemical data – hydrographic stations, profiling floats and subsurface drifters – gathered in March 2015. We use these data in order to characterize the impinging and outflowing currents and to describe the cross- and along-frontal thermohaline structure. In addition, we compare the in-situ measurements with both climatological data and the Mercator Ocean eddy-resolving reanalysis. The hydrographic sections illustrate the contrasting properties between the two western boundary currents: warm, salty, nutrient- and oxygen-poor oligotrophic subtropical waters carried southward by the BC and the cold, fresh, oxygen- and nutrient-rich subantarctic waters carried northward by the MC. The frontal system is also characterized by the presence of thermohaline intrusions, with the cross-frontal gradients and along-front velocities sharpening as the colliding currents shape the frontal system. We also observe brackish waters spreading on top of the frontal jet as a result of both the confluence dynamics and off-shelf advection favored by north-easterly winds. These low-salinity waters are positively correlated with surface ageostrophic speeds over the frontal jet. The cruise data illustrates the high regional and mesoscale variability as compared with climatological conditions, and further document the submesoscale subsurface complexity, which is not properly captured by available operational models
Paraules clau: Brazil-Malvinas Confluence Ocean currents River plume Ageostrophic velocity Lagrangian description Hydrographic data
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Pontes M., Salvador X., Parera A., Álvarez G., Ballesteros M. (2021)
Monografies de la Institució Catalana d’Història Natural, 3 DOI: 10.2436/20.1502.04.03. (BibTeX: pontes.etal.2021)
Resum: Veure
The Mediterranean Sea is a hotspot for biodiversity and endemic species (between 4 % and 18 % of known species are endemic, depending on the group), but this environment, favourable for native species, also favours exotic species. To ascertain how biodiversity has been impacted by intense human activity, we surveyed the marine life in the Barcelona Forum bathing area, an artificial beach receiving large amounts of waste from neighbouring areas and effluent from the nearby sewage treatment plant. Despite such eutrophic influences and the replacement of natural substrates with artificial ones, a surprisingly rich marine biota of 514 species was found. The groups with most species identified were molluscs (176), fish (88), crustaceans (65) and algae (50). These results include 15 exotic species that have settled in this ecosystem, such as the sea hare Bursatella leachii and the polychaete Branchiomma luctuosum, and some iconic natives such as the Fan mussel (Pinna nobilis) and the Dusky grouper (Epinephelus marginatus). Urban litter was sampled and no significant deleterious effects on the biota were detected. The site acts as a refuge for fish and is conducive to the settlement of encrusting species that colonize new substrates.
Paraules clau: Marinas, Biodiversity, alien species, marine litter, Barcelona Forum
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Rieger N., Corral A., Olmedo E., Turiel A. (2021)
Journal of Climate, 34, 24, 9861–9878. DOI: 10.1175/JCLI-D-21-0244.1. (BibTeX: rieger.etal.2021)
Resum: Veure
A proper description of ocean–atmosphere interactions is key for a correct understanding of climate evolution. The interplay among the different variables acting over the climate is complex, often leading to correlations across long spatial distances (teleconnections). On some occasions, those teleconnections occur with quite significant temporal shifts that are fundamental for the understanding of the underlying phenomena but that are poorly captured by standard methods. Applying orthogonal decomposition such as maximum covariance analysis (MCA) to geophysical datasets allows us to extract common dominant patterns between two different variables, but generally suffers from (i) the nonphysical orthogonal constraint as well as (ii) the consideration of simple correlations, whereby temporally offset signals are not detected. Here we propose an extension, complex rotated MCA, to address both limitations. We transform our signals using the Hilbert transform and perform the orthogonal decomposition in complex space, allowing us to correctly correlate outof-phase signals. Subsequent varimax rotation removes the orthogonal constraints, leading to more physically meaningful modes of geophysical variability. As an example, we have employed this method on sea surface temperature and continental precipitation; our method successfully captures the temporal and spatial interactions between these two variables for (i) the seasonal cycle, (ii) canonical ENSO, (iii) the global warming trend, (iv) the Pacific decadal oscillation, (v) ENSO Modoki, and finally (vi) the Atlantic meridional mode. The complex rotated modes of MCA provide information on the regional amplitude and, under certain conditions, the regional time lag between changes on ocean temperature and land precipitation.
Paraules clau: Atmosphere-ocean interaction, Teleconnections, Precipitation, Sea surface temperature, Empirical orthogonal functions, Pattern detection, Principal components analysis, Dimensionality reduction
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Rodero C., Olmedo E., Bardaji R., Piera J. (2021)
Sensors, 21, 5537 DOI: 10.3390/s21165537. (BibTeX: rodero.etal.2021)
Resum: Veure
Measuring the diffuse attenuation coefficient (Kd ) allows for monitoring the water body’s environmental status. This parameter is of particular interest in water quality monitoring programs because it quantifies the presence of light and the euphotic zone’s depth. Citizen scientists can meaningfully contribute by monitoring water quality, complementing traditional methods by reducing monitoring costs and significantly improving data coverage, empowering and supporting decisionmaking. However, the quality of the acquisition of in situ underwater irradiance measurements has some limitations, especially in areas where stratification phenomena occur in the first meters of depth. This vertical layering introduces a gradient of properties in the vertical direction, affecting the associated Kd . To detect and characterize these variations of Kd in the water column, it needs a system of optical sensors, ideally placed in a range of a few cm, improving the low vertical accuracy. Despite that, the problem of self-shading on the instrumentation becomes critical. Here, we introduce a new concept that aims to improve the vertical accuracy of the irradiance measurements: the underwater annular irradiance (Ea). This new concept consists of measuring the irradiance in an annular-shaped distribution. We first compute the optimal annular angle that avoids self-shading and maximizes the light captured by the sensors. Second, we use different scenarios of water types, solar zenith angle, and cloud coverage to assess the robustness of the corresponding diffuse attenuation coefficient, Ka. Finally, we derive empirical functions for computing Kd from Ka. This new concept opens the possibility to a new generation of optical sensors in an annular-shaped distribution which is expected to (a) increase the vertical resolution of the irradiance measurements and (b) be easy to deploy and maintain and thus to be more suitable for citizen scientists.
Paraules clau: annular irradiance; water quality; marine citizen science; diffuse attenuation coefficient; oceanography; light
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Schild K.M., Sutherland D.A., Elosegui P., Duncan D. (2021)
Geophysical Research Letters, 48, 3 DOI: 10.1029/2020GL089765. (BibTeX: schild.etal.2021b)
Resum: Veure
Increasing freshwater input to the subpolar North Atlantic through iceberg melting can influence fjord-scale to basin-scale ocean circulation. However, the magnitude, timing, and distribution of this freshwater have been challenging to quantify due to minimal direct observations of subsurface iceberg geometry and melt rates. Here we present novel in situ methods capturing iceberg change at high-temporal and -spatial resolution using four highprecision GPS units deployed on two large icebergs (>500 m length). In combination with measurements of surface and subsurface geometry, we calculate iceberg melt rates between 0.10–0.27 m/d over the 9-day survey. These melt rates are lower than those proposed in previous studies, likely due to using individual subsurface iceberg geometries in calculations. In combining these new measurements of iceberg geometry and melt rate with the broad spatial coverage of remote sensing, we can better predict the impact of increasing freshwater injection from the Greenland Ice Sheet.
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Sotillo M.G., Campuzano F., Guihou K., Lorente P., Olmedo E., Matulka A., Santos F., Amo-Baladrón M.A., Novellino A. (2021)
Journal of Marine Science and Engineering, 9, 4, 401. DOI: 10.3390/jmse9040401. (BibTeX: sotillo.etal.2021)
Resum: Veure
River freshwater contribution in the European Atlantic margin and its influence on the sea salinity field are analyzed. The impacts of using a new river discharge database as part of the freshwater forcing in a regional ocean model are assessed. Ocean model scenarios, based on the CMEMS (Copernicus Marine Environment Monitoring Service) operational IBI-MFC (Iberia Biscay Ireland Monitoring Forecasting Centre) model set‑up, are run to test different (observed, modeled and climatological) river and coastal freshwater forcing configurations throughout 2018. The modelled salinity fields are validated, using as a reference all known available in-situ observational data sources. The IBI model application is proven to adequately simulate the regional salinity, and the scenarios showcase the effects of varying imposed river outflows. Some model improvement is achieved using the new forcing (i.e., better capture of salinity variability and more realistic simulation of baroclinic frontal structures linked to coastal and river freshwater buoyancy plumes). Major impacts are identified in areas with bigger river discharges (i.e., the French shelf or the northwestern Iberian coast). Instead, the Portuguese shelf or the Gulf of Cadiz are less impacted by changes in the imposed river inflows, and other dynamical factors in these areas play a major role in the configuration of the regional salinity.
Paraules clau: river freshwater discharges; operational ocean models; sea surface salinity field, IBI region, LAMBDA river database, IBI model validation, model sensitivity tests
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Umbert M., Gabarro C., Olmedo E., Gonçalves-Araujo R., Guimbard S., Martínez J. (2021)
Remote Sensing, 13, 3828 DOI: 10.3390/rs13193828. (BibTeX: umbert.etal.2021)
Resum: Veure
The overall volume of freshwater entering the Arctic Ocean has been growing as glaciers melt and river runoff increases. Since 1980, a 20% increase in river runoff has been observed in the Arctic system. As the discharges of the Ob, Yenisei, and Lena rivers are an important source of freshwater in the Kara and Laptev Seas, an increase in river discharge might have a significant impact on the upper ocean circulation. The fresh river water mixes with ocean water and forms a large freshened surface layer (FSL), which carries high loads of dissolved organic matter and suspended matter into the Arctic Ocean. Optically active material (e.g., phytoplankton and detrital matter) are spread out into plumes, which are evident in satellite data. Russian river signatures in the Kara and Laptev Seas are also evident in recent SMOS Sea Surface Salinity (SSS) Arctic products. In this study, we compare the new Arctic+ SSS products, produced at the Barcelona Expert Center, with the Ocean Color absorption coefficient of colored detrital matter (CDM) in the Kara and Laptev Seas for the period 2011–2019. The SSS and CDM are found to be strongly negatively correlated in the regions of freshwater influence, with regression coefficients between −0.72 and −0.91 in the studied period. Exploiting this linear correlation, we estimate the SSS back to 1998 using two techniques: one assuming that the relationship between the CDM and SSS varies regionally in the river-influenced areas, and another assuming that it does not. We use the 22-year time-series of reconstructed SSS to estimate the interannual variability of the extension of the FSL in the Kara and Laptev Seas as well as their freshwater content. For the Kara and Laptev Seas, we use 32 and 28 psu as reference salinities, and 26 and 24 psu isohalines as FSL boundaries, respectively. The average FSL extension in the Kara Sea is 2089–2611 km2, with a typical freshwater content of 11.84–14.02 km3. The Laptev Sea has a slightly higher mean FSL extension of 2320–2686 km2 and a freshwater content of 10.15–12.44 km3. The yearly mean freshwater content and extension of the FSL, computed from SMOS SSS and Optical data, is (as expected) found to co-vary with in situ measurements of river discharge from the Arctic Great Rivers Observatory database, demonstrating the potential of SMOS SSS to better monitor the river discharge changes in Eurasia and to understand the Arctic freshwater system during the ice-free season
Paraules clau: arctic; freshwater fluxes; remote sensing; physical oceanography; sea surface salinity; ocean color; data fusion
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Vargas-Yáñez M., Juza M., García-Martínez M.C., Moya F., Balbín R., Ballesteros E., Muñoz M., Tel E., Pascual J., Vélez-Belchi P., Salat J. (2021)
Frontiers in Marine Science, 8, 640535 DOI: 10.3389/fmars.2021.640535. (BibTeX: vargasyanez.etal.2021)
Resum: Veure
The analysis of a 24-year time series of Conductivity-Temperature-Depth (CTD) casts collected in the Balearic Channels (1996–2019) has allowed detecting and quantifying long-term changes in water mass properties in the Western Mediterranean. For the complete period, the intermediate waters have experienced warming and salting at rates of 1.4°C/100yr and 0.3–0.6/100yr for the Western Intermediate Water, and 1°C/100yr and 0.3–0.4/100yr for the Levantine Intermediate Water. The density of these two water masses has not changed. The deep waters, defined as those denser than 29.1 kg/m3, showed positive trends in temperature, salinity, and density (0.8°C/100yr, 0.2/100yr, and 0.02 kg.m–3/100yr, respectively). The high temporal variability of the upper layer makes the detection of long-term changes more difficult. Nevertheless, combining CTD data with temperature data from the oceanographic station at L’Estartit and simulated data from the NCEP/NCAR reanalysis, it can be established that the Atlantic Water increased its temperature at a rate of 2.1–2.8°C/100yr and likely its salinity at a rate of 0.6/100yr. The water column absorbed heat at a rate equivalent to 1–1.2 W/m2. All these trends are much higher than those reported in previous works (more than double in some cases). The warming of the water column produced an increase in the thermosteric component of sea level. However, this increase was compensated by the decrease in the halosteric component. Besides these changes, other alterations related to the Western Mediterranean Transition have been observed over shorter periods. The temperature and salinity of the intermediate waters increased before the winter of 2004/2005 and then the temperature and salinity of the deep waters increased dramatically in 2005. The density of the deep water reached values unprecedented before 2005. Deep and intermediate waters were uplifted by the presence of such dense deep waters. The arrival of warmer and saltier intermediate waters from the Eastern Mediterranean is also observed, mainly after 2010.
Paraules clau: water mass properties, linear trends, climate change, Balearic Channels, Western Mediterranean Transition
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Viúdez A. (2021)
Physics of Fluids, 33, 054103 DOI: 10.1063/5.0048128. (BibTeX: viudez.2021)
Resum: Veure
Solutions of robust axisymmetric neutral vortices, that is, vortices with zero amount of vorticity, in two-dimensional (2D) Euler flows with distributed vorticity are obtained. These solutions are particular linear combinations of vorticity layer-modes, which are defined as truncated, shifted, and conveniently normalized Bessel functions of order-0, each one occupying a circular layer defined by a zero of the Bessel function of order-1. It is found that some linear combinations of these modes have a vanishing net amount of vorticity and remain axysimmetrically robust to small amplitude vorticity perturbations. These neutral vortices are quiescent and remain steady in the presence of similar vortices. Other linear combinations of these vorticity layer-modes give rise to unstable neutral vortices that develop into neutral tripoles, pentapoles, etc. It is found numerically that the robustness of these neutral vortices is related to the spiralization and axisymmetrization of the initially growing vorticity disturbances as are advected by a convex azimuthal velocity distribution beyond its first inflection point. In particular, it is found that two co-rotating neutral tripoles attract due to the phase synchronization of their respective octupolar potential flow but repel when touched due to vorticity exchange. This interaction mechanism makes possible equilibrium states for sets of a large number of neutral tripoles. Other linear combinations of these vorticity layer-modes give rise to non-neutral shielded vortices which interact and may form coherent vortex structures as pairs of co-rotating shielded vortices sharing their outermost vorticity layer or counter-rotating shielded vortices translating with uniform speed as vortex dipoles
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Wagenknecht K., Woods T., García-Sanz F., Gold M., Bowser A., Rüfenacht S., Ceccaroni L., Piera J. (2021)
Data Intelligence, 3, 1, 136-149. DOI: 10.1162/dint_a_00085. (BibTeX: wagenknecht.etal.2021a)
Resum: Veure
Citizen Science (CS) is a prominent field of application for Open Science (OS), and the two have strong synergies, such as: advocating for the data and metadata generated through science to be made publicly available [1]; supporting more equitable collaboration between different types of scientists and citizens; and facilitating knowledge transfer to a wider range of audiences [2]. While primarily targeted at CS, the EU-Citizen. Science platform can also support OS. One of its key functions is to act as a knowledge hub to aggregate, disseminate and promote experience and know-how; for example, by profiling CS projects and collecting tools, resources and training materials relevant to both fields. To do this, the platform has developed an information architecture that incorporates the public participation in scientific research (PPSR)—Common Conceptual Model①. This model consists of the Project Metadata Model, the Dataset Metadata Model and the Observation Data Model, which were specifically developed for CS initiatives. By implementing these, the platform will strengthen the interoperating arrangements that exist between other, similar platforms (e.g., BioCollect and SciStarter) to ensure that CS and OS continue to grow globally in terms of participants, impact and fields of application.
Paraules clau: Citizen Science; Metadata; Open Science; Public participation in scientific research (PPSR)
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Yahia H., Schneider N., Bontemps S., Bonne L., Attuel G., Dib S., Ossenkopf-Okada V., Turiel A., Zebadua A., Elia D., Kumar Maji S., G. Schmitt and J.F. Robitaille F. (2021)
Astronomy and Astrophysics, 649, A33 DOI: 10.1051/0004-6361/202039874. (BibTeX: yahia.etal.2021)
Resum: Veure
Observations of the interstellar medium (ISM) show a complex density and velocity structure, which is in part attributed to turbulence. Consequently, the multifractal formalism should be applied to observation maps of the ISM in order to characterize its turbulent and multiplicative cascade properties. However, the multifractal formalism, even in its more advanced and recent canonical versions, requires a large number of realizations of the system, which usually cannot be obtained in astronomy. We present a self-contained introduction to the multifractal formalism in a “microcanonical” version, which allows us, for the first time, to compute precise turbulence characteristic parameters from a single observational map without the need for averages in a grand ensemble of statistical observables (e.g., a temporal sequence of images). We compute the singularity exponents and the singularity spectrum for both observations and magnetohydrodynamic simulations, which include key parameters to describe turbulence in the ISM. For the observations we focus on the 250 μm Herschel map of the Musca filament. Scaling properties are investigated using spatial 2D structure functions, and we apply a two-point log-correlation magnitude analysis over various lines of the spatial observation, which is known to be directly related to the existence of a multiplicative cascade under precise conditions. It reveals a clear signature of a multiplicative cascade in Musca with an inertial range from 0.05–0.65 pc. We show that the proposed microcanonical approach provides singularity spectra that are truly scale invariant, as required to validate any method used to analyze multifractality. The obtained singularity spectrum of Musca, which is sufficiently precise for the first time, is clearly not as symmetric as usually observed in log-normal behavior. We claim that the singularity spectrum of the ISM toward Musca features a more log-Poisson shape. Since log-Poisson behavior is claimed to exist when dissipation is stronger for rare events in turbulent flows, in contrast to more homogeneous (in volume and time) dissipation events, we suggest that this deviation from log-normality could trace enhanced dissipation in rare events at small scales, which may explain, or is at least consistent with, the dominant filamentary structure in Musca. Moreover, we find that subregions in Musca tend to show different multifractal properties: While a few regions can be described by a log-normal model, other regions have singularity spectra better fitted by a log-Poisson model. This strongly suggests that different types of dynamics exist inside the Musca cloud. We note that this deviation from log-normality and these differences between subregions appear only after reducing noise features, using a sparse edge-aware algorithm, which have the tendency to “log-normalize” an observational map. Implications for the star formation process are discussed. Our study establishes fundamental tools that will be applied to other galactic clouds and simulations in forthcoming studies.
Paraules clau: ISM: structure / ISM: individual objects: Musca / turbulence / ISM: clouds / magnetohydrodynamics (MHD)