Spin-scanning Cameras for Planetary Exploration: Imager Analysis and Simulation

In this thesis, a novel approach to spaceborne imaging is investigated, building upon the scan imaging technique in which camera motion is used to construct an image. This thesis investigates its use with wide-angle (≥90° field of view) optics mounted on spin stabilised probes for large-coverage imaging of planetary environments, and focusses on two instruments. Firstly, a descent camera concept for a planetary penetrator. The imaging geometry of the instrument is analysed. Image resolution is highest at the penetrator’s nadir and lowest at the horizon, whilst any point on the surface is imaged with highest possible resolution when the camera’s altitude is equal to that point’s radius from nadir. Image simulation is used to demonstrate the camera’s images and investigate analysis techniques. A study of stereophotogrammetric measurement of surface topography using pairs of descent images is conducted. Measurement accuracies and optimum stereo geometries are presented. Secondly, the thesis investigates the EnVisS (Entire Visible Sky) instrument, under development for the Comet Interceptor mission. The camera’s imaging geometry, coverage and exposure times are calculated, and used to model the expected signal and noise in EnVisS observations. It is found that the camera’s images will suffer from low signal, and four methods for mitigating this – binning, coaddition, time-delay integration and repeat sampling – are investigated and described. Use of these methods will be essential if images of sufficient signal are to be acquired, particularly for conducting polarimetry, the performance of which is modelled using Monte Carlo simulation. Methods of simulating planetary cameras’ images are developed to facilitate the study of both cameras. These methods enable the accurate simulation of planetary surfaces and cometary atmospheres, are based on Python libraries commonly used in planetary science, and are intended to be readily modified and expanded for facilitating the study of a variety of planetary cameras

Inner FoV Stitching of Spaceborne TDI CCD Images Based on Sensor Geometry and Projection Plane in Object Space

High-quality inner FoV (Field of View) stitching is currently a prerequisite step for photogrammetric processing and application of image data acquired by spaceborne TDI CCD cameras. After reviewing the technical development in the issue, we present an inner FoV stitching method based on sensor geometry and projection plane in object space, in which the geometric sensor model of spaceborne TDI CCD images is used to establish image point correspondence between the stitched image and the TDI CCD images, using an object-space projection plane as the intermediary. In this study, first, the rigorous geometric sensor model of the TDI CCD images is constructed. Second, principle and implementation of the stitching method are described. Third, panchromatic high-resolution (HR) images of ZY-1 02C satellite and triple linear-array images of ZY-3 satellite are utilized to validate the correctness and feasibility of the method. Fourth, the stitching precision and geometric quality of the generated stitched images are evaluated. All the stitched images reached the sub-pixel level in precision. In addition, the geometric models of the stitched images can be constructed with zero loss in geometric precision. Experimental results demonstrate the advantages of the method for having small image distortion when on-orbit geometric calibration of satellite sensors is available. Overall, the new method provide a novel solution for inner FoV stitching of spaceborne TDI CCD images, in which all the sub-images are projected to the object space based on the sensor geometry, performing indirect image geometric rectification along and across the target trajectory. At present, this method has been successfully applied in the daily processing system for ZY-1 02C and ZY-3 satellites