Laser Remote Sensing of the Ocean: Methods and Applications , Alexei Bunkin and Konstantin Voliak Wiley, New York, 2001. $99.95 (244 pp.). ISBN 0-471-38927-7
Although hydrographic applications are the focus of Alexei Bunkin and Konstantin Voliak’s Laser Remote Sensing of the Ocean , the title belies the book’s breadth: nearly half of the text is devoted to general, nonmarine techniques in laser remote sensing. The diverse range of topics covered includes airborne terrain mapping, Doppler measurement of wind speed, and the measurement of atmospheric composition, thermodynamic states, aerosol concentrations, and gaseous pollutants.
The book does not cover the most recent developments in the fast-moving area of ice and vegetation canopy-mapping lidars, made possible by advanced detector arrays and digitizers. It does, however, provide a review of much of the earlier literature, both Soviet and American. It also acts as a bridge between the hydrographic work through the 1980s of the General Physics Institute (GPI) of the Russian Academy of Sciences and US airborne laser practices at NASA’s Wallops Flight Facility in Virginia. This kind of remote-sensing research has many implications for remote environmental monitoring from aircraft.
Airborne and orbital lidars typically direct more than 1018 photons toward Earth’s surface each second. Some photons are scattered elastically at their original wavelength from the ground, and by Rayleigh and Mie scattering from water and clouds. A handful may be detected at the receiver. Time of signal arrival is the primary interest for mappers, whose spectral window is intentionally restricted to the transmitted frequency. In the visible spectrum—using doubled neodymium yttrium aluminum garnet (Nd:YAG) lasers at 532 nm—laser bathymetry can reach up to ten times the characteristic optical attenuation range, 50 m or more, before the signal is lost. Such penetration also makes possible the mapping of photo-synthetic pigments and suspended particles in depth, through scattering and induced emission. For inland and coastal mapping, aircraft lidar mapping with satellite navigation provides decimeter accuracy and is more cost-effective than sonar.
Inelastic (Raman, Brillouin) scattering yields additional information about the molecular composition of the atmosphere and hydrosphere. The authors provide a detailed theoretical and experimental treatment of the response of gases and liquids to laser illumination. The spectral scattering properties of the ocean may be digitized as functions of time. Spectral components of the Raman-scattered light depend on water-column temperature and salinity. Fluorescence of pigmented algae and inorganic material competes with Raman scattering in the temporally varying spectrum of returned light. Fluorescence permits quantification of sediment load and, through phytoplankton fluorescence, the major biota as well. Illuminated in the UV, petroleum oil spills may be identified: Fluorescence from lighter Ekofisk petroleum persists much longer than that from Arabian heavy oils.
This book should be a useful reference primarily for specialists in remote studies of the oceanic biosphere. Subjects are not always accurately indexed, the illustrations are monochromatic, and the equipment described is sometimes dated. But the book provides an excellent overview of the theory and practice of spectral lidar remote sensing for the evaluation of marine environments.
