Remote sensing image must be geocorrected traditionally based on ground control points (GCPs) which are surveyed in field or measured in map, but surveying and measuring are very time-consumed and labor-consumed. Now an air-to-ground positioning system has been developed by IRSA, CAS to be applied to airborne remote sensing, and this system can directly give the exact coordinates of sample points in the terrain. All these sample points are then used to geocorrect remote sensing image that is acquired simultaneously from the same airborne platform. The air-to-ground positioning system is constituted of DGPS, attitude measurement unit (AMU) and laser scanning range finder (LSRF). DGPS can locate the position of airborne platform, AMU which is developed from gyroscope and is combined with GPS can accurately record the roll, pitch and heading of the airborne platform, while LSRF can measure the distance from platform to the sample point at terrain. According to geometry principle we can get the coordinate of each sample point from air. When the sample points and the remote sensing image are acquired simultaneously using the same scanning optical system, then all these sample points may be thought as the GCPs to geocorrect the image and can also be used to generate DEM. In this paper, the positioning principle of the air-to-ground positioning system and the error propagation are presented.
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