We use reference images from the USGS Robotic Lunar Observatory (ROLO) to take into account the inhomogeneous surface and the variations by lunar libration and phase to parameterise the location of the intensity centroid from the observation geometry. The viewing direction is steered towards the intensity centroid of the illuminated part of the lunar disk. Moon over limb port measurements use for both the vertical and the horizontal direction the adjustment by the SFD. In horizontal direction, SCIAMACHY's sun follower device (SFD) is used to adjust the viewing direction.
In sun over limb port observations, we utilise the vertical scans over the solar disk. sun and moon, to detect possible mispointings. The basic principle is the same as used by the star tracker: we measure the viewing direction towards celestial objects, i.e. In this work, we present additional sources of attitude information from the SCIAMACHY measurements itself. 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. The SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) on Envisat (2002–2012) performed nadir, limb, solar/lunar occultation and various monitoring measurements.
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