Atmospheric correction assessment of SPOT-6 image and its influence on models to estimate water column transparency in tropical reservoir

Remote sensing images have been increasingly used by its ability to collect data from extensive areas in a short time and with relatively low cost. Studies conducted in aquatic environments require great attention in relation to atmospheric correction, since the signal leaving water bodies is strongly attenuated. The present work aimed to assess the atmospheric correction of SPOT-6 image based on the variation of initial visibility parameter in FLAASH and analyze its influence on models to estimate Secchi depth (SD) and diffuse attenuation coefficient (Kd). The study was carried out in Nova Avanhandava Reservoir, which belongs to the chain of the Tietê River reservoirs (São Paulo, Brazil). The models calibration was based on remote sensing reflectance (Rrs) of simulated SPOT bands from data collected in the field. The best models were obtained using the band ratio Rrs(560 nm)/Rrs(660 nm) for SD (R2=92%, RMSE =11.45%) and the band Rrs(660 nm) for Kd (R2=92%, RMSE =11.98%). Maps of the spatial distribution of SD and Kd were made by applying the models on atmospherically corrected images. The main problem was the high amount of negative pixels when the suitable initial visibility value was not adopted in the atmospheric correction, which prevents the use of bio-optical models to retrieve limnological variables of the reservoir.