A Coupled Retrieval Of Columnar Water Vapor and Canopy Water Content From Spaceborne Hyperspectral Measurements

Imaging spectroscopy allows to identify and quantify water in different states based upon their discriminative absorption lines in the solar spectrum. We developed a coupled columnar water vapor (CWV) and canopy water content (CWC) retrieval method for spaceborne hyperspectral measurements like DESIS, PRISMA or the upcoming EnMAP mission. We linked the MODTRAN radiative transfer code to a surface reflectance model based on the Beer-Lambert law and quantified uncertainties using the maximum likelihood estimation. We simulated EnMAP TOA radiances using a coupling of PROSPECT, HySimCaR and EeteS. CWV and CWC were retrieved showing an R2 of 0.991 and 0.965, respectively. We observed a systematic overestimation of CWC by a factor of 3.374 since our model does not take into account volume scattering and different penetration depths within the canopy.