Earth reflectance and polarization intercomparison between SCIAMACHY onboard Envisat and POLDER onboard ADEOS-2

[1] In this paper, we compare reflectance and polarization measurements from two different satellite instruments, namely, the imager Polarization and Directionality of the Earth’s Reflectances (POLDER) and the spectrometer Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). Both instruments are able to measure not only the Earth reflectance but also the state of linear polarization of the detected light. The aim of this paper is to validate the SCIAMACHY reflectance and polarization data using the fact that POLDER is well calibrated. This validation requires a careful search for suitable, collocated data having identical solar and viewing angles. For the reflectance, there is a disagreement between POLDER and SCIAMACHY of up to 20% in the wavelength interval 400–1000 nm, which we attribute to SCIAMACHY. As for the linear polarization, we present for the first time clear evidence for the existence of discrepancies in the SCIAMACHY polarization retrieval for polarization measurement devices 2, 3, and 4.