Abstract
Abstract. Chang'E-1(CE-1) and Chang'E-2(CE-2) are the two lunar orbiters of China's lunar exploration program. Topographic mapping using CE-1 and CE-2 images is of great importance for scientific research as well as for preparation of landing and surface operation of Chang'E-3 lunar rover. In this research, we developed rigorous sensor models of CE-1 and CE-2 CCD cameras based on push-broom imaging principle with interior and exterior orientation parameters. Based on the rigorous sensor model, the 3D coordinate of a ground point in lunar body-fixed (LBF) coordinate system can be calculated by space intersection from the image coordinates of con-jugate points in stereo images, and the image coordinates can be calculated from 3D coordinates by back-projection. Due to uncer-tainties of the orbit and the camera, the back-projected image points are different from the measured points. In order to reduce these inconsistencies and improve precision, we proposed two methods to refine the rigorous sensor model: 1) refining EOPs by correcting the attitude angle bias, 2) refining the interior orientation model by calibration of the relative position of the two linear CCD arrays. Experimental results show that the mean back-projection residuals of CE-1 images are reduced to better than 1/100 pixel by method 1 and the mean back-projection residuals of CE-2 images are reduced from over 20 pixels to 0.02 pixel by method 2. Consequently, high precision DEM (Digital Elevation Model) and DOM (Digital Ortho Map) are automatically generated.
Highlights
Chinese Lunar Exploration Program (CLEP), usually known as the Chang’E program is a program of robotic and human missions to the Moon undertaken by the China National Space Administration (CNSA) (Wikipedia, 2012)
Based on the rigorous sensor model, the 3D coordinate of a ground point in LBF can be calculated by space intersection from the image coordinates of the conjugate points in stereo images, and the image coordinate can be calculated from 3D coordinate by back-projection
In order to reduce the inconsistencies of stereo images and improve mapping precision, we propose two methods to refine the rigorous sensor model: 1) refining exterior orientation parameters (EOPs) by correcting the attitude angle bias, 2) refining the interior orientation model by calibration of the relative position of the two linear CCD arrays
Summary
Chinese Lunar Exploration Program (CLEP), usually known as the Chang’E program is a program of robotic and human missions to the Moon undertaken by the China National Space Administration (CNSA) (Wikipedia, 2012). CE-1 orbiter is the first lunar probe of China launched on October 24, 2007 It carries a three-line push-broom CCD camera which has a ground resolution of 120m and a swath width of 60km at 200km orbit altitude. It is implemented on an area array CCD sensor and uses only the 11th, 512th and 1013th rows to generate the forward-, nadir-, and backward-looking images simultaneously in the flight direction (Li et al, 2010; Peng et al, 2010). Comparing with the three-line array mode of CE-1 CCD camera, CE-2 adopts a two-line push-broom camera to reduce the pressure of mass data, and assures stereo imaging condition (Zhao et al, 2010b) It can acquire forward- and backward-looking images simultaneously to consist stereo pairs. Experimental results with CE-1 and CE-2 images are presented to demonstrate the effectiveness of the proposed methods
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