Reflectance comparison between SCIAMACHY and a radiative transfer code in the UV

SCIAMACHY, onboard Envisat, is an Earth-monitoring spectrometer over the wavelength range 240-2400 nm. We compare its reflectance measurements in the UV with calculations by a polarised radiative transfer code for a cloud-free state over the Sahara desert. The SCIAMACHY reflectance between 240 and 400 nm is found to be too low by about 15-25%. The estimated error on this is less than 5%. The comparison method we present here can also be helpful for the in-flight calibration of other UV satellite spectrometers (like OMI, or GOME-2).