Underwater Acoustic Scattering from Lake Surfaces. I. Theory, Experiment, and Validation of the Data

Abstract

A statistical analysis, based directly on ensemble averages, is made of reverberation data obtained from the wind-driven surface of a fresh water lake. To produce the reverberation, two types of signals consisting of gated (linear “chirp”) FM or CW pulses, are transmitted with a carrier frequency of 110 kHz. In the CW cases the pulse durations are 0.1 and 1.0 msec. The bandwidth of the FM signals (pulse durations 1.25 msec) is 9.6 kHz, and operation in all instances is monostatic (R@T). In the CW experiment the grazing angle is 22°, and in the FM experiment the grazing angle is 0°. Particular care is taken to insure that a valid sample ensemble is obtained by testing each sample ensemble for independence (from a one-sample runs test) and homogeneity (by a suitable Kolmogorov-Smirnov test). A recently developed point scattering model is introduced and adapted to the present experimental geometry to provide a theoretical description of the reverberation and a basis for later comparisons with the data. From this model covariance functions and intensities of the scattered signal are determined and quantitative insight obtained regarding the nonstationarity of the reverberation process.