Determination of Sciamachy Line-of-sight Misalignments

Certain geolocation parameters derived in the early analyses of SCIAMACHY's limb measurements deviated from the expected values. After a corrective action in the ENVISAT flight operation segment concerning state vector parameters the situation improved significantly. However small inconsistencies persisted. These include a still existing bias and a leftright asymmetry in the limb tangent heights. We assume that the inconsistencies originate in additional small line-of-sight misalignments. This view is supported by azimuth/elevation features observed in solar occultation and sub-solar measurements around times when scanner control is switched from prediction to Sun Follower. In a model approach we use these specific measurements of SCIAMACHY to quantitatively determine extra misalignments in pitch, roll and yaw. The approach uses the features in elevation and azimuth to simulate misalignment effects. The determined extra misalignments will be used in operational tangent height retrievals.