Localized changes in the density of water induced by the presence of an acoustic field cause
perturbations in the localized refractive index. This relationship has given rise to a number of
nonperturbing optical metrology techniques for recording measurement parameters from underwater
acoustic fields. A method that has been recently developed involves the use of a Laser Doppler
Vibrometer (LDV) targeted at a fixed, nonvibrating, plate through an underwater acoustic field.
Measurements of the rate of change of optical pathlength along a line section enable the
identification of the temporal and frequency characteristics of the acoustic wave front. This
approach has been extended through the use of a scanning LDV, which facilitates the measurement
of a range of spatially distributed parameters. A mathematical model is presented that relates the
distribution of pressure amplitude and phase in a planar wave front with the rate of change of optical
pathlength measured by the LDV along a specifically orientated laser line section. Measurements of
a 1 MHz acoustic tone burst generated by a focused transducer are described and the results
presented. Graphical depictions of the acoustic power and phase distribution recorded by the LDV
are shown, together with images representing time history during the acoustic wave propagation
