12 research outputs found
Regional Assessment of COCTS HY1-C/D Chlorophyll-a and Suspended Particulate Matter Standard Products over French Coastal Waters
No full textChlorophyll-a (Chla) and suspended particulate matter (SPM) are key indicators of water quality, playing critical roles in understanding marine biogeochemical processes and ecosystem health. Although satellite data from the Chinese Ocean Color and Temperature Scanner (COCTS) onboard the Haiyang-1C/D satellites is freely available, there has been limited validation of its standard Chla and SPM products. This study is a first step to address this gap by evaluating COCTS-derived Chla and SPM products against in situ measurements in French coastal waters. The matchup analysis showed robust performance for the Chla product, with a median symmetric accuracy (MSA) of 50.46% over a dynamic range of 0.13–4.31 mg·m−3 (n = 24, Bias = 41.11%, Slope = 0.93). In contrast, the SPM product showed significant limitations, particularly in turbid waters, despite a reasonable performance in the matchup exercise, with an MSA of 45.86% within a range of 0.18–10.52 g·m−3 (n = 23, Bias = −14.59%, Slope = 2.29). A comparison with another SPM model and Moderate Resolution Imaging Spectroradiometer (MODIS) products showed that the COCTS standard algorithm tends to overestimate SPM and suggests that the issue does not originate from the input radiometric data. This study provides the first regional assessment of COCTS Chla and SPM products in European coastal waters. The findings highlight the need for algorithm refinement to improve the reliability of COCTS SPM products, while the Chla product demonstrates suitability for water quality monitoring in low to moderate Chla concentrations. Future studies should focus on the validation of COCTS ocean color products in more diverse waters
Combining an Eddy Detection Algorithm with In-Situ Measurements to Study North Brazil Current Rings
No full textNorth Brazil Current (NBC) rings are believed to play a key role in the Atlantic Ocean circulation and climate. Here, we use a new collection of high-resolution in-situ observations acquired during the EUREC4A-OA field experiment together with satellite altimetry to define, with unprecedented detail, the structure and evolution of these eddies. In-situ observations reveal a more complex structure than previously documented. In particular, we highlight a measurable impact of the Amazon outflow in creating a barrier layer over a large portion of the eddies. We show that this unprecedented data set allows us to estimate the accuracy of satellite altimetry gridded fields. The geostrophic velocities derived from satellite altimetry turn out to be considerably lower (up to 50% in amplitude) than the values measured by current meters. However, eddy properties as detected by TOEddies, a newly developed algorithm show to be relatively precise. For example, the eddy center and maximum azimuthal velocity contour fall within 25 ± 5 km and 16 ± 9 km, respectively, from the in-situ observed values. We apply TOEddies to 27 years of satellite altimetry to investigate the generic NBC rings behavior. We found a mean generation rate of 4.5 ± 1.1 rings per year, and a strong seasonal cycle in all eddy properties
Evaluation of twelve algorithms to estimate suspended particulate matter from OLCI over contrasted coastal waters
No full textInternational audienceRemote sensing of suspended particulate matter (SPM) is crucial for water-quality monitoring, as it influences turbidity, light availability, or nutrient transport. This study aims to provide a comprehensive evaluation of twelve common and well-used SPM models for the Ocean and Land Color Instrument (OLCI) on-board Sentinel-3 satellite, based on different methods and assumptions, including estimation from water-leaving reflectance or proxies, a combination of semi-analytical equations, and machine learning algorithms. The models are tested in three stages: 1) performance assessment on in-situ measurements, 2) matchup exercise with OLCI and 3) visual assessment of satellite SPM products. The models are first tested on the GLORIA dataset (n = 767, 0.21 g.m -3 <SPM <2,626.82 g.m -3 ). The matchup analysis is then conducted in French coastal waters using the SOMLIT dataset (n = 71, 0.2 g.m -3 <SPM <722 g.m -3 ), based on the standard OLCI L2 remote sensing reflectance product. Finally, the visual assessment of the SPM maps provided by the twelve models is conducted for two French coastal sites. Results show that the algorithms proposed by Jiang et al. [Remote. Sens. Environ. 258, 112386 (2021)] and Novoa et al. [Remote. Sens. 9, 61 (2017)] exhibit the highest score and the most accurate retrievals when compared to in-situ measurements. However, the matchup exercise shows that the method from Jiang et al. demonstrates more overall accurate SPM retrievals (Error = 49.85%, Bias = 0.55%, RMSLE = 0.35, Slope = 1.06). The visual assessment of SPM maps reveals that this model displays a larger dynamic range, making it suitable for applications in regions with a wide range of SPM concentrations. The sensitivity of these models to the atmospheric correction procedure is further explored. When all OLCI spectra are taken into account for the matchup exercise, the performance of the algorithms from Han et al. [Remote. Sens. 8, 211 (2016)] improve, relative to the other one. Finally, the standard OLCI SPM product is evaluated, and the advantages of using the OLCI standard product over the MODIS one for studying coastal waters are discussed.</div
Mesoscale dynamics and transport in the North Brazil Current as revealed by the EUREC4A-OA experiment
No full textInternational audienceThe North Brazil Current (NBC) rings are key features for interhemispheric water transport, facilitating exchange between the South Atlantic and North Atlantic Ocean. However, significant uncertainties persist regarding the total volume transported by these structures and the water masses they advect. In this study, we integrate high-resolution in situ observations from the EUREC4A-OA field experiment with satellite altimetry to address these knowledge gaps. Using a novel methodology, we estimate that surface NBC rings transport approximately 1.5 Sv, while subsurface eddies contribute between 0.4 and 9.7 Sv, underscoring their critical role in the regional total transport. Combined, these transports may significantly contribute to closing the Atlantic Meridional Overturning Circulation transport at low latitudes. Surface NBC rings predominantly advect Salinity Maximum Waters and fresh waters from the Amazon River, whereas subsurface NBC rings play a critical role in transporting Eastern South Atlantic Central Waters, Western South Atlantic Central Waters, and Antarctic Intermediate Waters northward. We estimate that the heat transport by surface and subsurface NBC rings is 5.8 and 0.3 TW, respectively, which is significantly lower than previous findings. Overall, these findings underscore the pivotal role of subsurface NBC rings as conduits for South Atlantic Waters across the Equator to the tropical North Atlantic. This study confirms the intricate dynamics of NBC rings and their essential role in interhemispheric water transport
Mesoscale Dynamics and Transport in the North Brazil Current as revealed by the EUREC4A-OA experiment
No full textThe North Brazil Current (NBC) rings are a key mechanism for interhemispheric water transport, facilitating the exchange between the South Atlantic Ocean and the North Atlantic. However, significant uncertainties persist regarding the total volume transported by these structures and the properties of the water masses they advect. In this study, we integrate high-resolution in situ observations from the EUREC4A-OA field experiment with satellite altimetry to address these knowledge gaps. Using a novel methodology, we estimate that surface NBC rings transport approximately 1.5 Sv while subsurface eddies contribute between 0.4 Sv and 9.7 Sv underscoring their critical role in the regional total transport. Combined, these transports, may significantly contribute to closing the Atlantic Meridional Overturning Circulation transport at low latitudes. Surface NBC rings predominantly advect Salinity Maximum Waters and fresh waters from the Amazon River, whereas subsurface NBC rings play a critical role in transporting Eastern South Atlantic Central Waters, Western South Atlantic Central Waters, and Antarctic Intermediate Waters northward. We also found that the heat transports by surface and subsurface NBC rings are here evaluated at 5.8 TW and 0.3 TW which is much less than previous estimation. Overall, these findings underscore the pivotal role of subsurface NBC rings as conduits for South Atlantic Waters across the equator and the Tropical North Atlantic. This study confirms the intricate dynamics of NBC rings and their essential role into interhemispheric water transport
Lowered ADCP data during Maria S. Merian cruise MSM89
No full textLADCP measurements used a two-instrument configuration with two Teledyne RDI 300 kHz workhorse ADCPs mounted in down- and up-looking positions. Data collection and processing was performed according to recommendations in the GO-SHIP manual (Thurnherr et al., 2010)
ADCP current measurements (38 and 75 kHz) during Maria S. Merian cruise MSM89
No full textTwo Teledyne RDI Ocean Surveyor systems with 38 and 75 kHz transmission frequency were used. Data was processed with a software package developed at GEOMAR following the GO-SHIP standards (Firing and Hummon, 2010). The data was subsequently averaged over one minute intervals and converted to a NetCDF based format
Moving vessel profiler (MVP) data collected during Maria S. Merian cruise MSM89
No full textThe Moving Vessel Profiler (MVP) is a CTD system that can be deployed from a moving ship, allowing for the sampling of water masses at high horizontal resolution with high accuracy of pressure, temperature, conductivity and other attached sensors. Processing of the data includes a fall-rate dependent correction of the thermal lag of the conductivity sensor and follows the approach described by Ullman and David (2014) for Underway CTD (UCTD) systems. Subsequently the corrected data was calibrated against the calibrated coincident Thermosalinograph and the calibrated nearby CTD data
Physical oceanography (CTD) during Maria S. Merian cruise MSM89
No full textSeabird 911plus systems equipped with dual temperature-conductivity-oxygen sensors were employed. All systems had a 24-bottle water sampling rosette with 10 l Niskin bottles. Water sampling, processing, and calibration followed GO-SHIP recommendations (Swift, 2010; McTaggart et al., 2010; Uchida et al., 2010) and included the recommended steps Data Conversion, Sensor Time-Alignment, Creation of Bottle Files, Outlier Removal, Pressure Sensor Filtering, Conductivity Cell Thermal Mass Correction, Ship Roll Correction and Deck Offset Correction by Loop Editing, as well as Derivation of Calculated Properties. After these steps, conductivity and oxygen readings were calibrated against values determined with salinometry and Winkler titration , respectively. Finally, the downcast data was averaged over 1 dbar wide intervals. An independent upcast calibration was used to obtain calibrated CTDO values coincident with the discrete water samples
Underway CTD data collected during Maria S. Merian cruise MSM89
No full textThe UCTD is a CTD system that can be deployed from a moving ship, allowing for the sampling of water masses at high horizontal resolution (ranging from less than 1 km for the Rapidcast system to 10 km for deep UCTD casts) with good accuracy of the pressure, temperature, and conductivity sensors. Processing of the data involved mostly the fall-rate dependent correction of the thermal lag of the conductivity sensor and followed the approach described by Ullman and David (2014). Subsequently the corrected data was calibrated against the calibrated coincident Thermosalinograph and the calibrated nearby CTD data.
The typical accuracies of the final pressure, temperature, and salinity data are 1 dbar, 0.01 °C, and 0.01 g/kg, respectively
