Oral Session 3

Vicarious Calibration and Validation of the Watersat Imaging Spectrometer Experiment In Québec Coastal Waters

The Watersat Imaging Spectrometer Experiment (WISE), an airborne hyperspectral sensor prototype, was deployed for validation and benthic ecosystem mapping during two fieldwork in optically shallow waters along the Estuary and Gulf of St Lawrence. Coincidentally to the WISE flights, in-situ water reflectance was measured with above-water and underwater radiometers at fixed stations, and along transects with a platform (jetski) combining in-water radiometers and acoustic sensors for bottom depth and type. The jetski transects covered various benthic surfaces, including mud, sand, rock, and micro and macroalgae. The first objective of the present study was to check the robustness of the actual absolute calibration from the manufacturer and to perform a vicarious calibration of WISE. In-situ measurements of water reflectance and aerosol optical thickness were used as input to the 6S atmospheric radiative transfer model. The at-sensor radiance modeled with 6S was compared with the WISE matchup measurement to derive the vicarious calibration gains. The gains values show a good agreement with a previous vicarious calibration performed with land targets and the MODTRAN atmospheric radiative transfer model. However, our results also suggest the importance of consistency in the method used for vicarious calibration and atmospheric correction. The second objective was to adapt the dark spectrum fitting atmospheric correction algorithm implemented in ACOLITE for airborne sensors. We applied ACOLITE to WISE imagery and validated the retrieved water reflectance in both optically shallow and deep waters. Our results highlight the difficulties of water reflectance validation in optically shallow water with a heterogeneous benthic substrate.

*Raphael Mabit, L’Institut des Sciences de La Mer de l’Université du Québec à Rimouski (ISMAR UQAR), Canada, https://orcid.org/0000-0002-5341-873X

Gabriela Ifimov, Aerospace, National Research Council, Canada

Raymond Soffer, Aerospace, National Research Council, Canada

Yanqun Pan, Arctus Inc., Canada

Soham Mukherjee, l’Université du Québec à Rimouski (UQAR), Département de Biologie, Chimie et Géographie, Canada

Simon Bélanger, l’Université du Québec à Rimouski (UQAR), Département de Biologie, Chimie et Géographie, Canada

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