Measurement of Phase of the Surface Reflection Coefficient Using Two Harmonically-Related Signals.

Two harmonically-related signals maintain a constant relative phase when propagating over identical paths in a nondispersive medium. This property was examined theoretically and experimentally to determine its usefulness in gaining certain information about a reflecting surface. Specifically, the research question was the following: If two harmonically -related signals of known initial phase are propagated simultaneously over the same path, reflected, and then detected, can the phase angle of the complex surface reflection coefficient be determined by comparing the two reflected signals?. The theoretical study resulted in equations which show the reflection coefficient to be a function of frequency and of the material properties (sound velocity, density, and absorption) of a medium and a reflecting or boundary surface. These specialized equations were used to predict the amplitude and phase of the reflection coefficient for a variety of materials based on published values of their material properties. An underwater acoustic experiment was conducted using collinear, harmonic acoustic signals. These signals were reflected from a number of different material samples. Values of measured parameters compared closely with predicted values. The answer to the question is affirmative for the following conditions: (a) The incident medium is nondispersive, and (b) The phase angles of the complex reflection coefficients are approximately equal for both frequencies.