Influence of Attitude Parameters on Image Quality of Very High-Resolution Satellite Telescopes
Walid A. Wahballah, Fawzy Eltohamy, Taher M. Bazan
Abstract
The image quality of very high-resolution satellite telescopes (VHRSTs) is affected by several factors, including optics, detector, pointing accuracy errors, attitude stability errors, and altitude variations. The charge-coupled devices with a time delay and integration (TDI) feature play a significant role along with the satellite attitude parameters in characterizing the VHRST image quality. The imperfection of the satellite control system to maintain the required pointing accuracy and attitude stability can lead to severe degradation in the quality of the acquired imagery. Hence, it is required to investigate their impacts carefully during the satellite preliminary design phase. In this article, the combined effect of the TDI steps, satellite attitude parameters, and orbital altitude variations on the image quality are investigated in detail. The results show that the image quality in the along- and cross-track directions are affected seriously in certain situations by the roll and pitch angular velocity bias. Furthermore, the proposed mathematical model in this article reveals that total modulation transfer function (MTF), as an image quality metric, is affected severely by the satellite altitude variation, particularly when employing a high number of TDI steps. For example, for a given scenario, when employing TDI steps of 64, the mathematical results show that the effect of a satellite altitude variation of 10 km will result in a 65% reduction in total system MTF.