Analysis of Suspended Sediment Variability in a Large Highly Turbid Estuary Using a 5-Year-Long Remotely Sensed Data Archive at High Resolution

International audienceSpatial variability of surface suspended particulate matter (SPM) concentration in the Gironde estuary and their relationships with environmental forcing are investigated through high spatial resolution multispectral data collected from July 2013 to August 2018 by the Operational Land Imager (Landsat-8/OLI) and MultiSpectral Instrument (Sentinel-2/MSI). A principal component analysis using the T-mode orientation is applied to the discontinuous multiannual time series composed of 41 remotely sensed images. The three first principal components (PC1, PC2, and PC3) explain 65.7% of the total variance. The SPM distribution associated with PC1 and PC2 exhibits a privileged along-estuary direction of the oscillation modes, while the spatial patterns of PC3 are clearly dominated by lateral oscillations opposing channels and shoals. The main environmental factors affecting the SPM distribution are identified by the analysis of their temporal patterns. The tidal range and the daily river discharge control the spatial patterns of PC1 and PC2, while the tidal cycles and the wind speed are significantly correlated with PC3. Furthermore, the analysis in the along-estuary and lateral directions shows marked longitudinal and transverse SPM gradients and a strong control of bathymetry on the SPM spatial distribution. For the first time, we highlight that the maxima of surface residual turbidity are located on the shoals regardless of the environmental (tidal and hydrological) conditions. Compared to previous studies, usually based on single-point in-water column measurements, these results provide a novel and complementary description of the spatial variability of SPM. They are useful to validate sediment transport numerical models, but also may improve our understanding of suspended sediment dynamics in estuarine systems governed by an estuarine turbidity maximum

Volume Changes of Lake Bracciano During the Sentinels Acquisition Period

International audienceLakes and reservoirs are considered sentinels of climate and anthropogenic changes. Lakes and reservoirs surface water storage is an essential hydrological variable but poorly known as this information is scarce. Earth Observation data are a reliable source of information to overcome this scarcity. Among these, the combined use of satellite images, to derive water extent, and radar altimetry, which enables to estimate water levels, provides valuable information on water storage changes. Here, we used Synthetic Aperture Radar images from Sentinel-1 and radar altimetry data from Sentinel-3 to monitor the water volume changes of Lake Bracciano from 2016 to 2021. This lake was affected by a water crisis in 2017 and the water supply to the city of Rome (Italy) was interrupted September 2017 to preserve its ecosystem. Hence, we demonstrate how Sentinel-1 and Sentinel-3 data can be useful to monitor water extent and level, which can be profoundly changed by the climate crisis