Launched in 2010

"Mapping Satellite-1 "（ TH-1） is the first stereo surveying and mapping satellite from China.During thereal operation of TH-1 in the space environment

the attitude angles of the star sensor

lens geometric parameters

and CCD undergo unpredictable changes that affect the positioning accuracy of satellite images. This study conducts self-calibration block adjustment research on TH-1 satellite images to achieve high image positioning accuracy. The following investigation method is used in this study: First

the lens and CCD geometric distortions of the three linear stereo surveying and mapping cameras of TH-1 are analyzed

and a self-calibration model suitable for the satellite’s three linear CCD images is proposed. The self-calibration block adjustment model is built for the satellite’s three linear CCD images. Overall adjustment is then applied on exterior orientation elements and self-calibration parameters to eliminate systematic errors present in the above observations and to improve the positioning accuracy. Finally

the Songshan testfield is utilized to support the self-calibration block adjustment processing for the three linear images of TH-1 and to verify the correctness and validity of the self-calibration and self-calibration block adjustment models.The influence of the number of control points on self-calibration is also analyzed. Experimental results demonstrate that using the self-calibration block adjustment technique can effectively eliminate systematic positioning errors and significantly improve positioning accuracy. The spatial resolution of the three linear array images of TH-1 is 5 m. After normal block adjustment

the optimal plane accuracy along the X- and Y-directions are approximately 20 m

with a height accuracyofapproximately 20 m and plane accuracy of 4 pixels. After self-calibration block adjustment

the optimal plane accuracy increased from 5 m to 6. 5 m（ i. e.

less than1. 3 pixels）

and the height accuracy increased to 5 m. Through a series of experimental research and analysis

the following conclusions can be drawn:（ 1） The auxiliary orbit and attitude determination files of the three linear CCD images of TH-1 contain clear systematic errors. A certain degree of geometric deformation also exists in the camera lens and CCD component. For direct space intersection using orbit and attitude determination files

a prominent systematic positioning error must be eliminated through the block adjustment approach.（ 2） If the self-calibration parameter Xsand its observation equation are not considered

Eq.（ 10）becomes the normal block adjustment model. Normal block adjustment considers only the control point error Xgand exterior orientation element error X; thus

it corrects only the attitude errors. Although normal block adjustment can effectively eliminate the positioning error caused by the attitude angle error

the impact of the lens and CCD component geometric deformation parameters still exists. The variation of the latter parameters is minor in a medium period

and the residual errors in the plane and elevation direction are still systemic.（ 3） Applying self-calibration block adjustment to the three-line array images of TH-1 with the self-calibration model presented in this paper can effectively eliminate the attitude errors and the combined effects of the focal length change

lens

and CCD geometric deformation and significantly improve positioning accuracy. The residual systematic errors of the checkpoints are effectively eliminated after self-calibration adjustment

which confirms the correctness and effectiveness of the self-calibration parameter and self-calibration block adjustment models presented in this paper.（ 4） Increasing the control points can efficiently improve the accuracy of self-calibration block adjustment in an appropriate range

but when the number of control points reaches a certain degree

the adjustment accuracy stabilizes.