SCIAMACHY reflectance and polarisation validation: SCIAMACHY versus POLDER

We compare reflectance and polarisation as measured by the imager POLDER and the spectrometer SCIAMACHY. Both instruments measure the Earth reflectance and the linear polarisation of the incident radiation. Our goal is to validate SCIAMACHY using POLDER as a reference. A fruitful comparison is only possible if we restrict ourselves to suitable, collocated data having identical solar and viewing angles. For the reflectance, we find a disagreement between POLDER and SCIAMACHY of 10-20%. For the linear polarisation, there is also a significant disagreement. We attribute both results to the current calibration problems of SCIAMACHY.