A review of laser Doppler anemometry (LDA) and particle image velocimetry (
PIV) with their application to the measurement of sound is presented. The f
undamental principles behind LDA and PIV are discussed and extended to the
application of sound measurement. Special attention is paid to analysis of
LDA signals including the Hilbert transform, which enables amplitude inform
ation to be obtained about various frequency components of a signal and wav
elet analysis. which allows non-stationary signals to he accurately analyse
d. The influence of the refractive index variations in a medium due to a so
und wave on the laser beams of an LDA signal is discussed. Attention is als
o paid to acoustic streaming which arises due to high-intensity sound, and
PIV results are presented to demonstrate the effect. (C) 2001 Elsevier Scie
nce Ltd. All rights reserved.