Atmospheric Acoustic Remote Sensing , Stuart Bradley , CRC Press/Taylor & Francis, Boca Raton, FL, 2008. $119.95 (271 pp.). ISBN 978-0-8493-3588-4
Modern atmospheric acoustic remote sensing began in 1968 with L. G. McAllister’s invention of sodar, sonic detection and ranging, also known as echosonde. The term “echosonde” accurately depicts the physical process underlying the operation of an acoustic sounder, which uses echoes for remote sensing. Over the years, however, sodar has become the most commonly used term to designate those systems. Remote sensing of the atmosphere also uses radio acoustic sounding systems, or RASS.
Low-cost, commercially available sodar systems quickly appeared on the market in the 1970s, and many groups from around the world explored various applications for the technology. Today, several prominent companies manufacture sodar systems that are typically used to determine wind speed and direction, and information about the turbulent atmosphere. They are also increasingly used for wind measurements to monitor conditions affecting wind-energy generation and to study and understand the atmospheric boundary layer in relation to air pollution and in dispersion modeling.
A wealth of research papers published in journals and conference proceedings cover applications of acoustic remote sensing. The first comprehensive survey is in Acoustic Remote Sensing Applications (Springer, 1997), a selection of research articles edited by Sagar Singal. Almost 20 years earlier, Edmund Brown and Freeman Hall Jr had published their excellent article, “Advances in Atmospheric Acoustics,” in the 1978 issue of Reviews of Geophysics and Space Physics . But for nonexpert scientists and engineers who want to understand and implement the technology in their own research, no reliable reference on sodar systems and RASS has been available—until now.
Atmospheric Acoustic Remote Sensing by Stuart Bradley fills the gap. Written by an internationally recognized authority in the design and use of sodar systems and RASS, the book accomplishes what it aims to do: provide “a useful description of how atmospheric acoustic remote sensing systems work and [give] the reader insights into their strengths and limitations.” Bradley’s book begins with a brief introduction of the subject, followed by background materials on basic meteorology and sound propagation. The background on meteorology is a useful review for scientists somewhat familiar with the subject; however, someone reading about it for the first time would do well to consult the references Bradley provides for a more complete treatment. For example, Geoffrey Taylor’s “frozen turbulence” hypothesis is discussed, and that hypothesis is not introduced in the background chapters.
The book systematically explains the underlying operation of sodar systems, a feature that is the core and strength of the book. The discussion includes how beams of sound are formed, how scattered sound is detected, and how systems are designed to optimize retrieving atmospheric parameters. Bradley considers calibration issues and gives details on actual designs; he thus makes the connection between the hardware and theoretical considerations. In addition, he covers dish antennas, phased-array antennas, and mono-static and bistatic sodar systems. His treatment of signal processing, a major part of sodar design, is relatively thorough. Often the author skips the detailed theoretical analysis and instead presents an intuitive description of the science. Ample numerical examples provided throughout demonstrate the intuitive understanding that Bradley is striving to achieve; the book also includes 15 full-color images and five appendices. No attempt is made to provide exhaustive references, but many key references in the field are cited.
The book seems to lose a bit of momentum toward the end. Bradley gives only a brief overview of RASS, and his discussion regarding specific applications is even shorter. In fact, the book is often somewhat uneven. Sections that present detailed coverage and numerical examples are often followed by sections that are terse. The text also shows evidence of perfunctory editing and proofreading. For example, in some of the figures, labels for the x-axis and y-axis are missing, and in a number of places in the text, equations are incorrectly cited. For instance, on page 96, equation 4.24 is given as the scattering cross section; however, equation 4.26 is the one that should have been cited. The last chapter seems to have missing or mislabeled figures.
Despite such minor blemishes, Atmospheric Acoustic Remote Sensing is a welcome contribution to the field of acoustic remote sensing. Moreover, it will be most useful for nonexpert scientists and engineers who wish to increase their knowledge of sodar and RASS—without muddling through the sometimes cursory treatment of the subject by manufacturers and without blindly diving into a huge body of literature.