Homography-Based Change Detection for Space-Based Satellite Inspection

In order to maintain space situational awareness, it is necessary to maintain surveillance of objects in Earth orbit. A system of space-based imaging sensors could make much more detailed inspections of the existing resident space objects (RSOs). However, in order to preserve bandwidth, it is desirable to send the groundstation only a subset of all images which are taken by the inspection system. This paper presents a change detection algorithm which can detect changes in the appearance of an RSO. A new inspection image is compared to a previously taken base image. In each image, the translation vector and rotation matrix between the camera and the RSO, or pose, is slightly different. Assuming that the points making up each image of the RSO are within a single plane, it is possible to generate a planar homography which is a linear mapping between the two images. The homography is used to estimate the rotation and translation between the camera coordinate systems. This knowledge can be used to warp the inspection image so that it appears as though it was taken from the same coordinate system as the base image. Finally, basic morphological image processing and image thresholding techniques are used to perform change detection. The algorithm was evaluated by applying it to raytraced inspection images exhibiting varying lighting and pose conditions. Simulation results show that the algorithm can reliably detect damage to the RSO or the rendezvous of a suspicious object.