Principles of Modern Radar - Volume 2 1891121537

6.10 References 255due to broadening of the PSR, (2) image artifacts such as multiple copies of a single object,and (3) a rise in the background noise. Two important methods for autofocus, or postprocessingimage enhancement, were presented. Autofocus is a standard component ofmany SAR image formation systems because it helps remove any residual phase errors thatare otherwise unaccounted for. A primary example is uncompensated platform motion.The SAR system parameters can be used to predict image contrast, which is a goodmeasure of image quality. This analysis is often used in the design stage to ensure that theentire hardware and software chain can produce imagery that meets the needs of the endusers. Besides thermal noise, major factors affecting image contrast are range and crossrangeambiguities, quantization noise, and the character of the point scatterer response inthe image itself. Image rating scales are also used to assess image quality. These are moresubjective, as they rate the image in terms of its ability to provide information for specifictasks. A radar capable of making fine resolution high-contrast imagery can still producepoor imagery. For example, a poorly chosen collection geometry might cause a town tobe obscured by shadows from nearby mountains.Readers interested in exploring spotlight SAR in more detail are encouraged to reviewthe books by Curlander and McDonough [3], Jakowatz et al. [4], and Carrara et al. [5].Together, these three volumes provide a thorough reference library for SAR system designand image formation. Curlander and McDonough [3] offer a comprehensive view of radarsystem engineering and explain many ideas from the standpoint of basic physics. It isoriented toward stripmap imaging, so the discussion of image reconstruction algorithmsis of limited use. Nevertheless, the authors provide many details of SAR system designthat are difficult to find elsewhere in the literature. The books by Jakowatz et al. [5] andCarrara et al. [4] offer a modern view of image formation. Carrara et al. is probably themost comprehensive reference on the subject of spotlight SAR up to and including imageformation. It is particularly valuable because it covers many real-world effects such asallowable deviations from an ideal flight path and correcting PFA imagery for wavefrontcurvature effects. Jakowatz et al. focus on the polar format algorithm and the projectionslice theorem, and these ideas are used to develop the procedures for change detection andinterferometry. Their discussion is particularly clear and accessible.A more recent reference is the February 2010 issue of IEEE Transactions on Geoscienceand Remote Sensing [35]. It is dedicated to the German TerraSAR-X satellitemission, and this issue contains articles on many interesting topics such as system design,calibration procedures, and advanced processing modes such as moving target detectionand sea current observation. There are many other books on the subject of SAR and itsmore advanced applications, some of which are discussed in Chapter 8. Although thebasics of image formation are largely settled, the SAR literature is constantly growing.Cutting-edge research is being performed by institutions in several countries, so it is alwayswise to follow the current literature for innovations and trends.6.10 REFERENCES[1] A. W. Love. In memory of Carl A. Wiley. IEEE Antennas and Propagation Society Newsletter,pages 17–18, June 1985.[2] Carl A. Wiley. The clipper ships of space. Astounding Science Fiction, 1951.[3] John C. Curlander and Robert N. McDonough. Synthetic Aperture Radar: Systems and SignalProcessing. John Wiley and Sons, Inc., 1991.