Characterizing Volume Reverberation Signals Using Level Crossing Information

Abstract

A point scatterer model is used to formulate expressions for the expected number of level and zero crossings of backscattered volume reverberation signals. It is shown that zero crossing measurements on narrow-band transmitted signals can yield quantitative estimates of scatterer population density in oceanic deep scattering layers. Level crossing data can be used to estimate scattering strengths. For wide-band transmitted signals, level crossing information can provide a relationship between scatterer Q and resonant frequency. Some features of using crossing data are (a) level and zero crossing systems are relatively simple to implement; (b) scattering strength measurements are independent of transmitted signal waveshape; and (c) since zero crossings are unaffected by the general time dependent decrease in reverberation level, zero crossing measurement systems do not require time-varying gain compensation. An experiment east of Bermuda compares scattering strength determination through level crossings to more conventional measurements. Also, the experiment gives scatterer density as a function of depth through a scattering layer. Peak densities of between 10−3 and 2 × 10−3 scatterers/m3 are found.