Offsetting Image Rotation System in FY-3 MERSI's Geolocation

45°rotating scan mirror is one of the most popular scanning modes in optics and fine mechanics, but out-of-axis misalignment will be brought about for the multi-detector combined scanning system because image rotation is caused by 45°rotating scan mirror. In order to obtain high resolution, multi-detector or linear sensor techniques are often adopted by current remote sensing instruments. For example, Chinese Ocean Color and Temperature Scanner (COCTS) on HY-1 satellite is a four-detector combined scanning scheme, 10 detectors and 40 detectors for sampling are adopted by the Medium Resolution Spectral Imager (MERSI) on FY-3 satellite. In order to eliminate this misalignment of image rotation, K mirror is applied in COCTS and MERSI to offset image rotation from 45°rotating scan mirror. A larger out-of-axis error in geolocation of remote sensing image will also be produced if the rotation and reflection of 45°rotating scan mirror is considered only but not the K mirror.An algorithmic model in the remote sensing image's geolocation is introduced. In the model, K mirror's reflection matrix is deduced and the error in remote sensing image's geolocation has been eliminated by vector reflection and rotation. First, the cause of image rotation from 45°rotating scan mirror is analyzed, then the processing method of "45°mirror & K mirror" offsetting image rotation system in the geolocation, including building the coordinate system and calculating the reflection matrix of 45°rotating scan mirror and K mirror, is presented. This model has been applied in FY-3 MERSI's geolocation. The categories of land and water have been searched from global Land Water Mask database according to longitude and latitude. It is proved by the geolocation results that this method can offset the error of image rotation. Finally, the error resources which are produced from "45°mirror & K mirror" offsetting image rotation system in geolocation are discussed.This model is also fit for the geolocation of other remote sensors that use 45°mirror and K mirror and multiple detectors.