Light Scattering by Nonspherical Particles: Theory, Measurements, and Applications

Abstract

Almost all solid particles and very many liquid drops are not spherical. In addition, particles may have internal structure, both homogeneous and heterogeneous, and there may be agglomeration. It has long been recognized that the well-known Mie theory for homogeneous spheres, and similar theories for simple shapes such as the infinite cylinder, are not adequate representations of the scattering by more complex shapes and structures. There may be significant differences in the calculated phase function to that in reality, and a theory for homogeneous spheres will completely fail to predict polarization effects. In the absence of rigorous analytical solutions for particles of general shape and structure, recourse is made to numerical techniques. The development of powerful computers has enabled these calculations to be performed rapidly and accurately for a wide range of particle types and sizes. The growth in numerical techniques has been exponential. For these reasons this book has come at a very opportune time, and is a welcome review of a large field of expertise. Authors who are recognized masters review each subject, and all the major methods are covered. For completeness there are also sections dealing with examples of practical applications of the calculations to nature. The book opens with a foreword by the renowned H C van de Hulst, who provides an interesting historical review and perspective. An introductory section of three chapters follows, dealing with fundamental concepts and definitions. The first of these deals with scattering by single particles and moves on to multiple scattering and radiative transfer. The second chapter is concerned with methods for nonspherical particles. It briefly reviews the limited exact theories available and then covers numerical and approximate methods. Finally, there is a chapter covering the basic properties of the scattering matrix for small particles. Overall, this section provides a most welcome review and grounding in the necessary basics of the subject. The next two sections form the backbone of the book and are concerned with reviewing developments in numerical techniques. The first of these has chapters covering the method of separation of variables, the discrete dipole approximation, the T-matrix method and the finite difference time domain (FDTD) technique. The second section pursues inhomogeneous particles with refractive index profiles, heterogeneous particles with inclusions, multiple interacting particles and aggregates. At the end of this section is a chapter reviewing developments to date in the theory of scattering by statistically irregular particles. This is very welcome in light of the fact that the bulk of natural particles are not regular in the sense that their shapes can be predicted. The latter part of the book is the province of measurements and applications. Here it is slightly less satisfactory, being perhaps a little narrower in scope. Under measurements there is a description of one experimental method for the determination of the elements of the Stokes matrix and a description of one microwave facility for large scale modelling of particles. The final section is a review of applications. This is largely concerned with environmental situations, covering LIDAR and radiative transfer methods for studies of clouds, microwave measurements of precipitation, scattering in marine environments and interplanetary dust. The book ends with a short chapter of biological applications. These are all interesting and useful illustrative examples, but I wonder whether a wider view may have been appropriate. Applications in industrial situations come to mind. In summary this is a very worthwhile research publication. It is attractively presented and comprehensive. It will prove to be a most useful addition to the literature in the ever-expanding field of light scattering. A R Jones