Chang’e-3（ CE-3） was successfully soft landed on the Moon on Saturday

December 14

2013. The descent camera onboard lander acquired a large amount of descent images during the landing process. In addition to visualization of the landing process to the public

these images are supportive for pinpointing locations of lander and rover after landing. With a detailed analysis of the geometric characteristics of these sequence descent images

we propose a method to recover the descending and landing trajectory using descent images with bundle adjustment techniques.Descending and landing trajectory can provide critical information of the motion state of lander during safe landing. So far

there is no report of recovery of descending and landing trajectory using descent images for Lunar or Mars landers. In this paper

we study the capability of trajectory recovery using CE-3 descent images. By fully utilizing the information of descent images

we r econstruct the trajectory and the three-dimensional terrain model of the CE-3 landing area. We provide a new approach to obtain-i ng the lander’s states in entry

descending

and landing phases. The derived Digital Terrain Model（ DTM） of landing area is of very high resolution and valuable in mission operations and scientific investigations.The method includes the following steps:（ 1） SIFT-based image matching is performed among the sequence images.（ 2）Match-i ng gross errors are eliminated by a RANSAC algorithm and the remaining matched points are used as tie points to form an image network.（ 3） Bundle adjustment of the image network is performed with control points which were acquired by matching the d escent images with a Digital Ortho Map（ DOM） generated from CE-2 images previously. As the output of bundle adjustment

the descending and landing trajectory is obtained

which includes the positions and attitudes of the lander when the descent images were taken. Based on the recovered trajectory

the lander’s states on entry

descending

and landing can be analyzed. DOM and DEM with much higher resolution than orbiter images have also been generated from the descent images.We obtain 26 control points and 18 check points from 1. 5 m resolution DOM and 4 m resolution DEM. The points are incorporated in the bundle adjustment. The RMS of control points and check points are 0. 60 m and 0. 75 m respectively. Based on the trajectory obtained from bundle adjustment

the lander’s motion state is analyzed

in which the speed curve and acceleration curve can reveal the engine thrust changes. The Digital Surface Model（ DSM） with a resolution of 0. 4 m has been produced and has been used in rover path planning and other mission operations. This method has been proved effective through applications in CE-3 m ission.