Investigations on the capability of CHRIS-PROBA for monitoring of water constituents in Lake Constance compared to MERIS

Abstract

CHRIS-PROBA data were acquired at 3 days in 2003 at the Eastern part of Lake Constance. Field campaigns were organised at these days in order to measure optical parameters of the water and the atmosphere and concentrations of water constituents from ship for validation. For two dates also MERIS full-resolution data are available. Based on the in-situ measurements, forward calculations were made to simulate for different conditions the expected CHRIS and MERIS top-of-atmosphere radiance spectra. The result is a comparison of CHRIS with MERIS and with simulated radiances. CHRIS spectra were reproduced in a satisfying way whereas MERIS spectra are disappointingly misaligned and have to be recalculated to exclude miscalculation as the source of this error. Further, the calculated spectra were adjusted to the measured ones by fitting the concentrations of 3 aerosol types (rural, maritime, urban) and 3 water constituents (suspended matter, chlorophyll, Gelbstoff). The values for concentrations of suspended matter and Gelbstoff have a mean relative difference of 16% and 26% respectively which is within the error margin of in-situ data, chlorophyll concentrations have a mean relative difference of 47%. All calculations were done using the modular inversion program MIP, which is being developed at DLR for processing multispectral and hyperspectral images from surface waters.