The Positioning of SPOT Stereo Images with a Local Orbit
Jung-Sheng Hsia and Ji-Rung Chen
Department of Surveying and Mapping Engineering,
Chung Cheng Institute of Technology,
Yuansulin, Tashi, Taoyuan, 335, Taiwan, R.O.C.
Tel: (886)-3-380-0364 Fax: (886)-3-380-0364 # 168
E-mail: jshsia @ccit.edu.tw
China Taipei
Abstract:
The research aims at using the SPOT satellite ephemeris data with suitable weight when the bundle adjustment of SPOT stereo images is carried. With the aids of the weighted ephemeris data, the degree of the stability of the adjustment process can be increased. In addition, the number of ground control points needed for starting the adjustment can be reduced. In the mean time, a reasonable result can be given. The model uses SPOT satellite ephemeris data to determine the positions and attitudes of scan lines where the image points used in the bundle adjustment are located. The positions and the attitudes became as observations weighted in the model of bundle adjustment. As a result of that, a local orbit for SPOT stereo images is available to be determined. This may stabilize the adjustment process and decrease the number of ground control points needed.
The research shows the results of a sub-pixel level of positioning precision when using some ground control points as well as SPOT satellite orbital and ephemeris data with suitable weights. The model works well even when the number of ground control points is reduced to few. And its result is better than that of intersection method without using ground control points.
1. Introduction
The positioning method using stereo SPOT images have been developed in several models since the SPOT satellite was placed in the orbital in 1986. One way of positioning can be carried out with auxiliary satellite position and attitude data while using SPOT imagery without ground control points. The positioning accuracy however became very low. A general model of using collinearity condition equations can give results in a sub-pixel level of positioning accuracy. Exterior orientation parameters of a SPOT image are given as polynomial functions of time with second or third order. Therefore, an essential number of ground control points and iterations for estimating the coefficients of the polynomials increases. With the aids of constraints, satellite position and attitude rates, the essential number of ground control points can be decreased and the accuracy of SPOT image orientation can be improved (Shibasaki et al., 1988). A method has been developed with the aims of decreasing the number of ground control
points and stabilizing the adjustment process with the assistant of local orbits estimated for each SPOT image by the use of auxiliary satellite position and attitude.
