Microwave imaging techniques, by Bernard D. Steinberg and Harish M. Subbaram, Wiley Series in Remote Sensing, Jin Au Kong, Ed., John Wiley & Sons, Inc., New York, 1991, 361 pp., $64.95, hardbound, ISBN 0‐471‐50078‐X

In microwave imaging a target is illuminated by a microwave transmitter, and the reflected or scattered energy is intercepted by a receiving antenna. The received microwave echoes are then processed to produce an image. The basic principle is the same as optical imaging in which the lens of a camera transforms the optical field at the lens into an image in the focal plane. Both optical imaging and microwave imaging require a sourcc of radiation, a reflecting or scattering surfacc, and rcceivers. Thc present book is the third book o f a series dealing with large arrays and microwave imaging. The first book. Principles of Aperture and Array System Design: Including Random and Adaptive Arrays (Wiley, 1Y76), introduced the designers of communications and radar systcms to the spatial domain. Its purpose was to bridge the gap between two disciplincs, one practiced by the antenna designer and the student of electromagnctics, and the other by the student of statistical communication theory and system design. While the first hook provided the intellectual basis for the study of large antenna arrays, the second one, Microwave lmuging with Large Antenna Arrays: Radio Camera Principles and Techniques (Wiley. 1983), was a how-to book describing the intrinsic problems of large microwave systems and ways to overcomc these problems. It demonstrated that it is possible to make very large antenna arrays that are highly distorted and highly thinned, and by using self-calibration procedures called adaptive beamforming to cause these arrays to produce microwave imagery as good as from diffraction-limited antennas. The primary thrust of this book was the achievement of high angular resolution in microwave imagery. The book recognized that high resolution was a ncccssary condition for high-quality imagery but that it was not a sufficient condition. I t left thc development of the subject “How To Make Good Microwave Pictures” to the present book. The present book is divided into two distinct parts. The first describes what microwave imagery is, how it is obtained, and what the problems are in obtaining good microwave images. This part consists of the first four chapters. Chapter I is an excellent introduction to the problems of microwave imaging, covcring terrestrial imaging systems and various measures of image quality. Chapter 2 deals with the necessary mathematics in a lucid and intuitive way, a strength of the book. Chapter 3, covering widcband effects, treats steering methods and concludcs with image processing in the computer. Chaptcr 4 addresses problems concerning long wavelengths, scattcring effects, and large-aperture effects. The remaining eight chaptcrs make up the second part of thc book. Thcy dcscribe many techniques for enhancing image quality. Chapters 5 and 6 deal with ways for achicving divcrsity-combining of images. Chapter 7 introduces dcconvolution for eliminating image artifacts and for the general improvement of image quality. An important feature is the interesting treatment of a technique called CLEAN, a method first dcvclopcd for radio astronomy. Chapters 8 and 9 discuss thc self-calibration mcthods necessary for successful operation of very large arrays. Chapter 10 describes means for rcducing the data-handling rcquirements of large, high-rcsolution phased-array systems. Chapter 11 treats thc theory and practice of super-resolution or non-Fouricr processing of spatial data. Espccially valuable is the treatment extcnding this method into the near field and applying it to microwavc imaging for the purpose of enhancing the available resolution from a given aperture. Much, but not all, of the work described in this book came out o f the authors’ experience at the Valley Forgc Research Center of the Moore School of Engineering of the University o f Pcnnyslvania. Very useful was the work at that Center on very high-resolution microwave imaging. Valuable experience was obtained from the large, complicated antenna arrays, including the 83-m array that for the first time providcd human-optical angular resolution at mircowaves. Display techniques found useful at the Valley Forge Research Center end the book in Chapter 12. The authors are always generous in acknowledging the work of their co-workers and students in this endeavor. The high quality of this book is evident from the successful integration of the theoretical with the practical. This book is a definitive work, and deserves the attention not only of students and workers in microwave imaging but in other fields where quality images are desired.