Retrieval of Trace Gas Concentrations from Lunar Occultation Measurements with SCIAMACHY on ENVISAT

Abstract

SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) is a UV-Vis-NIR spectrometer on-board ENVISAT, dedicated to measure atmospheric trace gas distributions in nadir, limb, and occultation geometries. In occultation mode, SCIAMACHY tracks the rising Sun or Moon directly through the atmosphere. Dividing the atmospheric measurements by extraterrestrial references gives transmission spectra, which are suitable for a DOAS-like retrieval approach. Here, we report on the major retrieved data products (ozone, NO2, and NO3) obtained from SCIAMACHY lunar occultation observations. We validated our ozone and NO2 data products. Ozone validation was carried out with other satellite instruments (HALOE, SAGE II, and POAM III). The NO2 results were validated with photochemically scaled HALOE and SAGE II profiles. The validation results reveal that the biases in the SCIAMACHY lunar occultation ozone and NO2 are within ±15%, with standard deviations and the uncertainties of the biases are less than 20% and 6%, respectively. Comparisons of NO3 results carried out with a 1-D photochemical model show that the accuracy of our NO3 data product is better than 30%.