The GOME-2 Level 1 Instrument Degradation Model Version 1 and its Application for Atmospheric Composition Retrievals

Abstract:

GOME-2 on Metop-A and -B is suffering from signal degradation in the shorter wavelength regime below 420 nm, like many instruments of this type. During its 8 years in orbit to date, GOME-2 on Metop-A has acquired enough data to enable correction of most (though not all) aspects of its signal degradation using a combination of empirical and instrument model correction. We present the first version of the GOME-2 Metop-A degradation model which covers the full spectral range between 240 nm and 790 nm and also includes signal correction for two polarisation measurement devices (PMDs). We discuss the individual model components, including a correction of the solar-spectrum and the calibration of the solar diffuser, a stray-light correction in the region below 295 nm, an angular correction of all earthshine data, as well as a correction in the spectral domain for low frequency patterns. The first version of the dataset covers the time period from launch until the start of tandem operations in July 2013, when the swath of GOME-2 Metop-A was reduced from 1920 km to 960 km.

We will discuss the individual degradation components accounted for, their physical origin, and will show the first results of the corrected spectra and their impact on level-2 retrieval quality. We also present the roadmap towards the implementation of a near real-time correction scheme of GOME-2 level-1 data and discuss various options concerning its potential operational and offline functionalities.