The need for three-dimensional measurements of velocity and at least its first derivatives is increasing in science as well as in technology. Moreover, velocity field measurements are necessary in many fields of fluid mechanics and related disciplines. In the first chapter of this volume recent developments in the traditional method of hot-wire anemometry are presented. Optical methods are increasingly used for velocity field measurements. Among them, Particle Image Velocimetry is, in practice, the best established. The state of the art in commercially available systems and a look at future developments are described in Chapter Two. Novel approaches to this topic, based on videogrammetric principles, are treated in Chapters Three and Four. Chapter Three treats the application of videogrammetry in Particle Tracking Velocimetry. The basic principles and their implementation are described in some detail. Performance tests show that the accuracy of the method is comparable to that of LDA.It is, however, a fully three-dimensional measuring technique, capable of determining long particle trajectories which are needed for the study of particle dispersion in turbulent flows and the associated Lagrangian statistics. Least Squares Matching is applied in Chapter Four to track in space three-dimensional patterns in small cuboids obtained by Laser-Induced Fluorescence Tomography. The method yields fully three-dimensional information on the velocity field, the vorticity field and the field of the rate of strain tensor. In addition, concentration distribution and its derivatives can be determined. It is a powerful, novel method for the study, not only of flow, but also of mixing processes. Special attention is given to presenting the basic theoretical aspects of these new methods as well as practical information needed for their application. This book is aimed at scientists and engineers involved in experimental work.
