The Comparison of Spectral Top-of-Atmosphere Reflectances Measured by AATSR, MERIS, and SCIAMACHY Onboard ENVISAT

The top-of-atmosphere reflectance measurements by advanced along-track scanning radiometer (AATSR), medium-resolution imaging spectrometer (MERIS), and scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) onboard ENVISAT have been compared for collocated scenes. The AATSR and MERIS observations were averaged to the scale of a SCIAMACHY ground scene (30 km times 60 km). The SCIAMACHY reflectances were averaged to account for much coarser spectral resolution of AATSR and MERIS observations. It was found that SCIAMACHY reflectances coincide with those of MERIS within 4% MERIS calibration error. This is also the case for AATSR reflectances, except at the wavelength of 0.865 mum, where SCIAMACHY gives, on average, 6% lower reflectances as compared to those of AATSR. They are 3% too low as compared to MERIS observations at this wavelength.