by Oleg I Yakovlev, Taylor & Francis 2002, ISBN 0415273501, £60 (€94).
The twinkling of radio sources due to propagation effects is a nuisance most of the time, and radio astronomers try hard to remove these effects and sharpen up their radio maps. However, the scintillation can also be used in a positive way to probe conditions in the Earth’s atmosphere and ionosphere, the interplanetary medium, the solar wind and the interstellar medium. For example, regular monitoring of the scintillations of extragalactic radio sources is now used to map out the interplanetary weather and the solar wind on a daily basis.
Artificial Earth satellites and deep-space probes have opened up even more elegant possibilities for remote sensing of planetary atmospheres and ionospheres and the solar wind. Satellites have many advantages compared with natural radio sources, as they are truly point-like and can transmit coherent monochromatic signals at several frequencies. Professor Yakovlev has devoted most of his scientific life to devising and interpreting such experiments. This extended monograph gathers together many of the insights he has gained, and provides a graduate-level introduction to this fascinating field of radio science. The book includes an extensive bibliography covering the period 1960-1999.
Chapter 1 starts with the basic physics of radio propagation through the Earth’s atmosphere and ionosphere between ground stations and spacecraft, and ends with the topical subject of ionospheric tomography, in which satellite systems (such as GLONASS and GPS) transmitting coherently at several frequencies are observed simultaneously from different locations on the ground. This is a powerful tool for studying the ionosphere.
Professor Yakovlev’s speciality, radio occultation studies, comes next. Reading between the lines I could glimpse the excitement of some of the early experiments. For example, the atmosphere of Venus is so thick that radio waves passing within 40 km of the surface are refracted by 6°, while waves that try to pass within 34 km of the surface of the planet suffer critical refraction and are captured. The radio occultation studies of the giant planets Jupiter, Saturn, Uranus and Neptune by the Pioneer and Voyager probes are outstanding achievements of space science in the 20th century. The same techniques have also been used to study the very rarefied plasmas around smaller bodies, including Halley’s Comet. Nearer to home, experiments between Mir and a geostationary satellite have demonstrated exciting possibilities for global monitoring of the Earth’s atmosphere using satellite-to-satellite paths at several frequencies.
The core of the book covers radio sounding of the solar wind and the interplanetary plasma. By ingenious application of the techniques already expounded, Yakovlev explains how to measure the scale sizes and velocities of irregularities in the solar wind, the magnetic field, how to study magnetosonic and Alfven waves, and much more. The book then changes direction slightly to deal with radar observations of planets, asteroids and comets, including detailed treatments of scattering from a rough surface, back scattering, effects of planetary rotation, bistatic radar experiments and sideways-looking synthetic-aperture radar. Finally there is a short, and to me disappointing, chapter covering basic principles for interstellar radio communications. This is fairly standard material, presented without the unique insights that make the rest of the book so much more interesting. Russian space probes have been monitored at Jodrell Bank since the early 1960s. Many of us wondered exactly what was going on up in Lab 5, and what became of the large number of data tapes forwarded to Russia. With the arrival of this book on my desk things have become clearer to me. I have enjoyed learning from an expert guide the joys of watching the signals twinkle and fade as spacecraft pass behind a planet.
