Improved pointing information for SCIAMACHY from in-flight measurements of the viewing directions towards sun and moon

Kurzfassung

SCIAMACHY on Envisat (2002–2012) performed nadir, limb, solar/lunar occultation and various monitoring measurements. The pointing information of the instrument is determined by the attitude information of the Envisat platform with its star trackers together with the encoder readouts of both the azimuth and the elevation scanner of SCIAMACHY. In this work, we present additional sources of attitude information from the SCIAMACHY measurements itself. The basic principle is the same as used by the star tracker: We measure the viewing direction towards celestial objects, i.e. sun and moon to detect possible mispointings. Using these measurements, we fit improved mispointing parameters by minimising the pointing offsets in elevation and azimuth. The geolocation of all retrieved products will benefit from this, especially the altitudes assigned to SCIAMACHY's limb and occultation products will be improved.