Time frequency investigation and representation of acoustic backscatter signatures

Abstract

Observation of an object’s structural acoustic response, considered in the aspect-dependent frequency response domain, is a data representation used for characterizing the target strength of an object. Geometric and elastic wave features in the angle-frequency domain are difficult to distinguish. Time varying characteristics such as attenuation are lost with a single frequency transform across the entire time collection of the acoustic return. Research in the aspect angle-frequency domain primarily applies the fast Fourier transform to an entire time series collection for a single ping cycle. This work aims to extend the dimensional space of analysis for the acoustic backscatter representation by investigating time-frequency resolution across aspect angle for acoustic elastic responses of an object. Empirical analysis of the data is presented with application of various time frequency transforms. These methods are assessed using time frequency localization metrics to quantify their performance with the AirSAS dataset. This exploratory work will develop the intuition regarding how the time frequency distribution can be localized, measured, and vary among objects of differing compositions. The ways in which time frequency localization can support distinguishing features of the acoustic return beyond the traditional aspect angle-frequency domain will be discussed as well.