{'fraction_non_alphanumeric': 0.019479188025425465, 'fraction_numerical': 0.004921058027475908, 'mean_word_length': 5.318652849740933, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 2, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Lidar. Range-Resolved Optical Remote Sensing of the Atmosphere, in the Springer Series in Optical Sciences, Vol. 102, edited by Claus Weitkamp

Advances in lidar have tracked and sometimes stimulated advances in laser technology. As Herbert Walther remarks in the Foreword, ‘Improvement of laser technology was vital in the lidar field. At first, researchers were mainly concerned with keeping the laser of their lidar system working; finally, they were able to concentrate on optimising the measurement procedure itself and spend the time evaluating their data.’ This book is a collection of 14 articles from 19 contributors covering the basic theory and current practice of lidar in a consistent and fairly uniform style. It should be very useful to readers who, like me, have some knowledge of the basics of lidar and some of the standard techniques but would like to learn more about the state of the art. The first chapter provides an overview of basic lidar techniques and the lidar equation. It sets the stage for the remaining chapters by including brief summaries of ‘the five basic lidar techniques’: elastic backscatter, differential absorption (DIAL), Raman scattering, resonance fluorescence, and Doppler. It is noted, correctly, that ‘Each of the following chapters is self-sufficient and can in principle be understood without knowing any other chapter.’ The different chapters are well written and include historical background as well as many references. The next two chapters review two general aspects of lidar, namely depolarisation and multiple scattering effects. Polarisation techniques were used in radar methods in the 1950s; a linearly polarised field is transmitted and the depolarisation ratio of the backscattered light is measured. The much smaller wavelength of laser radiation leads to much stronger depolarisation (from particles larger than the wavelength) and therefore to more powerful polarisation techniques. The chapter on ‘Polarisation in Lidar’ reviews the causes of depolarisation as well as lidar methods that make use of it particularly for studies of clouds and aerosols. The chapter on ‘Lidar andMultiple Scattering’ reviews in considerable detail the theory and modelling of multiple scattering, which is an especially important consideration in the case of clouds and fog. The next five chapters review the basic concepts and applications of the five basic lidar techniques listed above. A chapter on ‘Lidar and Atmospheric Aerosol Particles’ describes the various types of aerosols and how their characteristics are inferred from elastic (Rayleigh) and Raman scattering lidars. This is followed by a chapter on ‘High Spectral Resolution Lidar’ which provides among other things another way to discriminate (based on Doppler shifts) between the light scattered by molecules and the light scattered by aerosols. A chapter on ‘Visibility and Cloud Radar’ describes the use of lidar for assessing visibility and determining visual range at airports, for example; an interesting application under development is a lidar system using a laser diode and an avalanche photodiode for use in an ‘intelligent automobile tail light’ which will monitor visibility as well as the distance and speed of other vehicles, and adjust its brightness accordingly. Two chapters are devoted to DIAL, which has benefitted from developments in tunable lasers and optical parametric oscillators. One of these chapters focuses on ozone and industrial emissions and the other on water vapour and temperature profiling; both also review briefly the basic theory of DIAL based on the lidar equation. Another chapter is devoted exclusively to Raman lidar, which does not demand specific laser wavelengths or a high degree of laser spectral purity but requires a signal averaging because of the low (Raman) scattering cross-section. This chapter also provides a nice summary of the basic theory of Raman scattering. One of the most important uses of lidar is the temperature profiling of the atmosphere. A separate chapter devoted to this topic focuses on rotational Raman lidar and an integration lidar technique that obtains the temperature of different range bins via the scattering particle density ratios in successive range bins; rotational Raman lidar appears to be a very accurate way to determine vertical temperature profiles in the troposphere and lower stratosphere, whereas the integration method based on Rayleigh scattering works well for temperature profiling of higher altitudes. Temperature profiling is also done by resonance fluorescence lidar, the subject of the next chapter. That chapter focuses on laser-excited resonance fluorescence of sodium and other metallic constituents of the mesosphere to determine density and temperature profiles. Temperature profiling with Contemporary Physics Vol. 50, No. 5, September–October 2009, 601–613