Atmospheric correction for hyperspectral ocean colour remote sensing for the umpcoming EnMAP mission (ACENMAP)

A critical step for obtaining accurate retrievals of ocean colour remote sensing over waters from hyperspectral imagery is an effective atmospheric correction. Opposed to multispectral imagery, atmospheric scattering and absorbers have to be considered differently at the various spectral bands. Another challenge is the low signal of most water surfaces, which makes the atmospheric correction a crucial task to derive for the hyperspectral satellite mission EnMAP (Environmental Mapping and Analysis Program), with its expected signal-to-noise ratio, reliable water leaving reflectance measurements. The major goal of this project, ACENMAP, is to develop an efficient atmospheric correction over water with defined uncertainties. With simulated data by the coupled atmosphere-ocean radiative transfer model (RTM) SCIATRAN, atmospheric absorbing and scattering effects on TOA reflectance can be precisely located and accounted for in the correction scheme, as well as other effects as glint and due to the proximity to the coast (e.g. mixed land-water pixels). These simulations will also be used to develop a correction scheme for these effects, as well as for estimating water leaving reflectance from TOA reflectance data. The uncertainty will be derived from RTM simulations, intercomparison and validation with in situ water leaving reflectance and satellite TOA reflectance from multispectral sensors (e.g. MERIS). The developed algorithm will be tested on HICO and SCIAMACHY data (downscaled to EnMAP spectral resolution but keeping the spatial resolution) before EnMAP operation. After verification, the atmospheric correction scheme allowing the retrieval of water leaving reflectance will be implemented into the EnMAP box.