On Airborne and Spaceborne SAR Image Quality Analysis

Synthetic Aperture Radar (SAR) imagery combines the high-resolution properties of pulse- compressed radar, along-track beam sharpening through Doppler effect, and sophisticated digital signal processing techniques, in order to obtain a highly focused ground map based on the electromagnetic characteristics of the illuminated surface. Hence, the information content of a SAR image and the effect of surface features on radar imagery are quite different from infrared or conventional photography, and are useful for feature extraction by using multisensor data. A fundamental topic -preliminary to any scientific investigation on the data sets obtained from airborne or spaceborne SAR systems- is to evaluate quantitatively the quality of the raw data and of the processed images. A set of image quality measures which characterise both the raw data quality and the processor performance has to be defined, before accepting the data for distribution to the user and to the scientific community. This report is concerned with such a definition, and reviews the most widely used quality measurements both on raw data and on processed data. Due to the importance of the SAR processor in the end-to-end SAR system chain, the most important issue of the Image Quality Assessment (IQA) performed on final images consists in evaluating quantitatively the worsening with respect to ideal processing, by means of a set of parameters derived from the analysis of the SAR Impulse Response Function (IRF).