Multidate Quality Assessment Of Alsat-1 Satellite’s Imager

Control of image quality of an earth observation satellite must be permanently carried out during all orbit life. To achieve this, reference images of three types of targets were taken into consideration, by Alsat-1 (First Algerian launched Satellite) between early 2004 and late 2006: The first target is a homogeneous white region (clear snow) of the Antarctica and above the Arctic regions. The second target is a dark region taken by night over the Pacific Ocean in order to emphasize variations of dark noise, The third target is a clear area along the Rail Road Valley (Nevada, United States) in which radiation is measured on the ground and simultaneously to get the absolute calibration of on board instruments. The purpose of this paper is to assess the variation of the camera quality over a three years period of Alsat-1 operations, by analyzing the images reference taken in the period stated above. We also analyzed the channel light sensitivity (green, red and infrared) through a radiometric estimation, pixel by pixel of two images for a typical homogeneous site (scenes with a uniform background radiation) at two distinguished periods of time, while maintaining the same setting. This radiometric evaluation concerns two types of targets only (dark target and bright target). To this aim, we used a variety of assessment methods, all based on mathematical and algorithmic tools. They includes objective assessment such as PSNR (sigle de Peak Signal to Noise Ratio), entropy, AMBE (Absolute Mean Brightness Error-AMBE), etc.., and much more other subjective methods, such as visual analysis,use of statistical indicator, etc...