Retrieval of carbon monoxide, methane, and nitrous oxide from SCIAMACHY measurements

Abstract

The atmospheric spectrometer SCIAMACHY to be launched on board ESA's Envisat satellite in 2000 will measure UV, visible and IR spectra from nadir, limb and occultation with spectral resolution between 0.2 and 1.4 nm. SCHIAMACHY's channel 8 covering the wavelength range 2265-2380 nm will allow the global determination of concentrations of methane, carbon monoxide and nitrous oxide. Sensitivity studies using the most recent values for the instrument parameters show that the minimum values for the accuracies for total vertical columns are of order 5 Dobson units (DU) for carbon monoxide, 3 DU for methane, and 6 DU for nitrous oxide, for a 1 s SCIAMACHY nadir observation. The detection of the IR spectra features novel InGaAs detectors, specially developed for the SCIAMACHY project. While providing the required sensitivity in this wavelength domain, these detectors are limited by noise levels that vary strongly from pixel to pixel. This poses special challenges to the retrieval of molecule concentrations from the measured detector signals. Ways to overcome this problem are discussed.