Geoacoustic inversion of data collected in two ‘‘typical’’ shallow-water environments

Abstract

Two distinct types of shallow-water experiments were recently conducted by SACLANTCEN in different shallow-water areas (<150 m) to perform geoacoustic inversion of received acoustic signals. A towed sound source–horizontal line array was used in one of the experiments, and in the other the source and vertical array were moored on the bottom. The two experimental configurations were deployed in two areas with soft and hard bottom properties in order to investigate (1) the performance of geoacoustic inversion using horizontal and vertical line arrays, and (2) the robustness of the inversion method to different bottom characteristics. The transmitted signals were 1-s linear frequency modulated sweeps in the band from 200–800 Hz. The source–horizontal array separation was 300 m and the fixed path between the source and the vertical array was 2 km. This short source–receiver separation minimizes the impact of the range-dependent water-column and seabed properties on the acoustic propagation. The applied geoacoustic inversion technique of the data is the traditional model-based matched-field processing utilizing a global search algorithm. Results from successful geoacoustic inversion in the regions with soft-bottom properties are presented for the two experimental configurations. Severe difficulties appeared when inverting data from the hard-bottom regions and possible causes are given.