Long Term Monitoring of GOME/ERS-2 Calibration Parameters
Sander Slijkhuis(1), Melanie Coldewey(1), Sandra Wahl(1), Bernd Aberle(1) and Diego Loyola(1)
(1) German Aerospace Centre, DLR-IMF Oberpfaffenhofen, 82234 Wessling, Germany
After more than 10 years of successful operation and data processing, the extensive data set of the most important GOME in-flight calibration parameters in the GDP database has been investigated, in order to analyse the long-term stability of the instrument.
This study focuses on the wavelength calibration, especially on the selection of the spectral lines from the PtCrNe lamp measurements. Several lines were identified to be inappropriate because of their asymmetric shape and instability problems. They should not be used anymore in operational data processing, in order to ensure highest quality of the wavelength calibration.
The detector's pixel-to-pixel gain (PPG) correction is quite small over the whole life time of GOME, but nevertheless not negligible, especially for the minor absorbers (e.g. BrO). In channel 2 an increase of the RMS of the PPG by more than 70% was detected, between 1995 and 2002. In all channels an abrupt decrease took place at the beginning of 2002.
The detector's leakage current behaviour is very stable. It does not show effects similar to that of the PPG.
The intensity of the sun mean reference spectra show a strong decrease by more than 80% at 240 nm in channel 1, and by more than 40% at 310 nm in channel 2, due to instrument degradation and the ERS-2 pointing problem.
In the PMD Q-factor's time series, several peaks and outliers were found . These correlate with GOME instrument anomalies such as cooler switch-offs, instrument and satellite switch-offs, as well as special operations.
Apart from the degradation in instrument throughput, the analysed calibration parameters show a good stability over the entire mission time frame of GOME.
The results of this study will be used to further improve the GOME data products.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,