Analysis of LFM pulses received by a hydrophone array in shallow water

The report presents an analysis of linear FM pulses collected by a vertical 8-hydrophone receiver array in shallow water in the Stockholm archipelago in May 2001. The water depth at the trial site varied from 28 to 42 m, and the pulses were from an omnidirectional source at ranges 50 to 700 m from the receiver array. The source was located at depths 5 and 27 m. The purpose of the experiment was to (i) identify multiple arrivals in the data and estimate the arrival times, using pulse compression techniques by replica correlation. (ii) identify the propagation paths of the observed arrivals using sound propagation modelling by ray theory. (iii) if possible, estimate reflection coefficients at the seabed from bottom-reflected arrivals as a compliment of previous analyses with other techniques at the site. The data allowed identification of different arrivals in a few cases. For most experimental setups, surface echo arrivals could not be separated from direct arrivals. For the experiments where arrival separation could be done, the arrival time estimates from the sound propagation model fit the data well. Bottom echo arrivals could not be detected, except possible echoes of large bottom objects, located far from the experimental track.