Chapter 3: The Instrument

Abstract

The objective of the SCIAMACHY mission requires the instrument to be capable of determining concentrations of a large number of trace gas species over the full vertical extent of the atmosphere from the troposphere up to the mesosphere. In addition, aerosol properties as well as pressure and temperature shall be derived. Therefore SCIAMACHY was designed as a passive imaging spectrometer, comprising a scan mirror system, a telescope and a spectrometer, controlled by thermal and electronic subsystems. Scan mirrors, telescopes and spectrometer together form the optical assembly. The scan mechanisms permit steering the line-of-sight according to the required viewing geometries. Solar radiance and irradiance are dispersed by the spectrometer into 8 channels from the UV to the SWIR range. With signals gained from the calibration unit and the Polarisation Measurement Device, the spectral and radiometric calibration of the science channels can be maintained over the mission lifetime. Thermal stability is ensured via active and passive thermal control systems including the Radiant Cooler assembly. Those units which control the entire instrument and interface electrically with the ENVISAT platform are hosted by the Electronic Assembly. SCIAMACHY was developed in a combined effort of German, Dutch and Belgian space agencies, industry and scientists and ready for the ENVISAT launch in March 2002.