Martin, S.An Introduction to Ocean Remote Sensing, 2nd Edition. Cambridge University Press, ISBN 9781107019386, $85.

Abstract

I remember, about 30 years ago, when J. T. O. Kirk's (1983) book, “Light and Photosynthesis in Aquatic Systems” came out. Ocean bio-optics, a synergy between optical physicists and biological oceanographers, was in its infancy. We thought then that this was “the Bible” for bio-optics. While Kirk's book may not have had the theoretical rigor of Preisendorfer's (1976) “Hydrologic Optics,” it covered all the important aspects of the interaction of light and biology in aquatic systems. The present book, I thought, might be something similar for remote sensing of the ocean, but is instead, as indicated by the title, an introduction (a second edition; I had not seen the earlier one from 2004). It can be considered a first stop before embarking on a more in-depth (sorry) treatment. That said, as a first stop, Prof. Martin's book is invaluable, and rewards the reader with clear explanations, and discussions of the limitations and advantages of satellite remote sensing. The perspective favors the technical, for example, differentiating between what is signal at the satellite sensor and what is noise. The book proceeds in orderly fashion beginning with a background and the basics. Chapter 1, a must-read for novices and veterans alike, traverses definitions, orbits and imaging, and also a brief, but useful history. Martin defines remote sensing as “the use of electromagnetic radiation to acquire information about the ocean, land, and atmosphere without being in physical contact…” According to this definition, as he states, remote sensing will also include sensors on a ship or other platform, and even the spectrophotometer app on my iPhone. He focuses, however, on remote sensing using satellite sensors, and then proceeds to discuss what that lack of physical contact entails in terms of satellite orbits and scanners, resolution issues, and data processing. He covers the definitions and the description of various kinds of satellite sensors (passive vs. active, spectrometers, radars) and how they are designed to sweep and survey the ocean's surface. His history, near the end of Chapter 1, shows the evolution of satellites from demonstration projects, for example the NIMBUS series, and from large multi-instrument satellites the size of a city bus, to constellations of smaller platforms. Constellations mean instrument failures are less catastrophic, there is greater international cooperation, and technology is easier to keep up to date. Martin then proceeds (Chapter 2) to a consideration of ocean surface phenomena, followed in succeeding chapters by treatments of electromagnetic radiation, atmospheric interferences, and the air–sea interface. From there, he introduces ocean color, IR observations, microwave imagers, scatterometers, altimeters, and radars. There is a good treatment of the optical theory underlying the measurement of ocean geophysical variables (temperature, sea level, winds, ice, and color) from space. There is also an excellent discussion of the atmospheric correction, and how it is done when there is no provision in the satellite spectrometer for IR bands (as on the Coastal Zone Color Scanner), wavelengths where the ocean will not have much (or any) reflectance. There is also a good analysis of the necessity for vicarious calibration of ocean color sensors such as for the SeaWiFS and MODIS sensors. There is an excellent chapter on how SAR (synthetic aperture radar) works. A minor error is the identification, in Chapter 6, of “chlorophytes” or “coccolithophores” as species. Chlorophytes in this case refer to a composite: model output meant to represent a variety of phytoplankton groups. Coccolithophores are a group with many different species. The book deals more with the problem of detecting geophysical variables from space, with all the interferences, orbital considerations, and surface complexities (e.g., sea foam, capillary waves), at the expense examining ocean processes. To be sure, there are some examples of the use of the data, but readers will have to look further for how the magnitude and distribution of remote sensing variables help us understand ocean circulation, the movement of sea ice, seasonality, and ocean productivity. The book concerns itself more with “nuts and bolts,” calibration and validation. For myself, I'll place Martin's book on the shelf next to reports from the International Ocean Colour-Coordinating Group, some of which consider the applications of remote sensing to oceanography. Perhaps as an introductory text, there are omissions. There is no consideration of LandSat, even though that platform has applications in coastal areas. (NASA's Earth Observatory often has captivating images from coastal environments.) There is also no consideration of remote sensing from aircraft, nor, in a look to the future, a treatment of LIDARs, such as aboard the CALIPSO satellite. But overall, this is a fine treatment of satellite remote sensing of ocean properties that will find use among students, instructors, and researchers. Reviewed by John Marra, Earth and Environmental Sciences, Aquatic Research and Environmental Assessment Center, Brooklyn College, CUNY, NewYork, NY, USA; jfm7780@brooklyn.cuny.edu