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. Specialattention 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.

The contents of this volume reflect to a large extent the efforts made by a group of Institutes at the ETH Zurich to develop new techniques for measurements of flows in fluids in the last decade. The motivation came from the study of tr sport and mixing processes in natural and industrial systems. One of the characteristic properties of turbulence is its high mixing efficiency. The techniques developed are therefore suitable, although not exclusively, for turbulence measurements. They can be subdivided into point-measurements and field-measurements. The aim of the point-measurements developed is to determine the three components of the velocity and all their first derivatives with good temporal resolution and accuracy in turbulent flows. The old and weIl established method of hot-wire anemometry was used for this purpose. One of the main achievements in this context is the construction of miniature multi-wire probes. This technique was introduced to the Institute of Hydromechanics and Water Resources Management of ETH Zurich by Profs. A. Tsinober and E. Kit from Tel-Aviv University. This was made possible by the generous financial support by ETH, for which I would like to express my gratitude on this occasion. In addition, Dr. F.E. Joergensen from DANTEC contributed an example of recent developments in the hardware ofConstant Temperature Anemometry (CTA), for which I am very thankful."