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SCIAMACHY Monitoring Factors: Observation and End-to-End Correction of Instrument Performance Degradation.

Klaus Bramstedt(1), Stefan Noel(1), Heinrich Bovensmann(1), John P. Burrows(1), Thorsten Fehr(2), G√ľnter Lichtenberg(3), Christophe Lerot(4), Gijsbert Tilstra(5) and Angelika Dehn(6)

(1) University of Bremen, Otto-Hahn-Allee 1, D-28359 Bremen, Germany
(2) ESA/ESRIN, Via Galileo Galilei, 00044 Frascati, Italy
(3) German Aerospace Center (DLR), Oberpfaffenhofen, D-82234 Wessling, Germany
(4) Belgian Institute for Space Aeronomy, 3 Avenue Circulaire, B-1180 Brussels, Germany
(5) Royal Netherlands Meteorological Institute (KNMI), , De Bilt, Netherlands
(6) Serco S.p.A., Via Sciadonna, 24, 00044 Frascati, Italy

Abstract

SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) is a grating spectrometer in the UV-Vis-NIR spectral range. SCIAMACHY is part of the ENVISAT payload and since April 2002 in a sun-synchronous orbit, observing Earth's atmosphere in nadir, limb and occultation geometry. To ensure the SCIAMACHY data quality over the life-time of the instrument, its performance is continuously monitored. The throughput of instrument is monitored end-to-end by regular observations of the sun. From these measurements, the so-called monitoring-factors (m-factors) are calculated. Each light path of the instrument (nadir light path, limb/occultation light path, sun over diffuser light path) has its own set of m-factors. By applying the m-factors, a stable radiometric calibration of the radiances and irradiances from SCIAMACHY over mission lifetime can be ensured.

We describe the measurements, the calculations and the operational implementation of the m-factors. Based on the m-factors, the performance of the SCIAMACHY over seven years in orbit is assessed. Furthermore, first examples will be shown how the retrieval of atmospheric parameters benefits from m-factors.