Intercomparison of vertical column densities derived from SCIAMACHY Infrared Nadir Observations

Abstract

Nadir observations in the shortwave infrared channels of SCIAMACHY onboard the ENVISAT satellite can be used to derive information on CO, CH4, N2O, CO2, and H2O. Several scientific data analysis tools have been developed for retrieval of vertical column densities, and a significant upgrade of the operational level 2 data processor has been prototyped recently. WFM-DOAS, developed by University of Bremen, is a modified DOAS algorithm: A linearized radiative transfer model plus a low order polynomial is linear least squares fitted to the logarithm of the measured sun-normalized radiance. On the other hand, BIRRA (implemented at DLR) is a nonlinear least squares fit of the measured radiance. Trace gas vertical profiles are scaled in both cases to fit the observed data, further auxiliary parameters are code dependant. In this contribution we present results of an intercomparison of vertical column densities, nb. carbon monoxide, retrieved from SCIAMACHY infrared nadir observations.