Pulse compression in striation processing—Acoustic invariant as seen in the time domain

Abstract

The acoustic invariant is well known to produce broadband interference or striation patterns in spectrograms. These have been used for a variety of applications, including geo-acoustic inversion and target tracking, in both passive and active settings. The processing to extract parameters from these broadband interference patterns has typically been performed on the spectrograms. However, spectrogram striations have energy that is spread across a wide band. This paper will present a time domain approach, in which the striations are pulse-compressed via a correlation process, before extracting the parameters of interest. Narrowband signals pose an interesting conundrum for striation processing - they are typically much stronger iin level than the underlying broadband interference pattern, and can be mistaken for striations, thus corrupting the parameter extraction. As in time delay estimation, pre-whitening is needed to suppress narrowband components. At the same time, the narrowband components best reveal the underlying interference pattern, albeit in a very narrow band, because they are of such high SNR. We will discuss how to exploit this information content as well.