Oral Session 2 | Monday, October 3, 14:00–14:20 | Abstract 475

Nighttime observations of river discharges into coastal waters using the panchromatic band of VIIRS satellite sensor

The satellite remote sensing of river discharges into the ocean is of primary importance for a better understanding of the biogeochemical processes occurring in coastal ecosystems. The observation of these ecosystems is currently performed under solar illumination conditions for which the radiometric sensitivity of ocean color sensors is designed. The VIIRS sensor (NASA/NOAA) is equipped with a panchromatic camera (Day-Night-Band-DNB) that offers the opportunity of measuring extremely low level signals (about 10–5 W m–2 sr–1 ) from the Earth. Night observations of the ocean color is a promising field of research that has not yet been deeply undertaken. Here, the nighttime radiances as measured by the VIIRS DNB band are analyzed to investigate their relevance for the detection and monitoring of river plumes in turbid waters. The observations are studied over two coastal areas, namely the delta of Mekong (Vietnam) and Rhône (France) rivers. The sensitivity of the top of atmosphere radiances to the amount of the incident lunar irradiance is examined. It is shown that the radiance seasonal cycle is pronounced near the full moon phase. Daily river plumes could be satisfactorily distinguished, including for a weak lunar illumination (20% of full moon light). The influence of the adjacency effects caused by the diffuse glow from city lights on the magnitude of nocturnal radiances has been estimated. It could be as high as 45% over water targets, thus suggesting the preferential use of areas far from shorelines to properly observe water turbidity at night. Finally, the impact of the ocean dynamics, particularly the wind-driven current, on the spatial and temporal variations of nighttime radiances is examined for the case of river flooding events. This study demonstrates the high benefit of performing nighttime remote sensing measurements of the ocean color for the analysis of the transport of suspended matter in coastal areas. 

Malik Chami, LATMOS–Sorbonne Université, 000-0001-7815-0533

Zacharie Aoulad, OCA

Sébastien Migeon, Geoazur–Sorbonne Université

Audrey Minghelli, Université de Toulon

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