SWAC 4: Broadband Data Analysis Using Sub-Band Processing - Part 2

摘要

The frequency dependence of reverberation is examined using the processing method as for the frequency analysis of target detection during the same experiment. In this experiment, reverberation is induced by abrupt changes in the bottom bathymetry (a 200 m sea mount). For the analysis of the received signal a sub-band matched filter scheme is devised, according to which, a replica of the transmitted pulse (2300 Hz-3500 Hz LFM signal) is segmented into ten 120 Hz sub-bands, each of which is processed independently through a matched filter detector. Following the necessary corrections for array gain and calibration, transmitted power spectrum and propagation loss, the matched filter data are compared to reveal the frequency dependence of reverberation. Due to insufficient in situ measurements, the propagation loss estimate is based on model calculations - a challenging task for the range dependent seafloor at the experimental site. After examining a large number of pings it is concluded that the reverberation energy calculated at the correlator output is comparable for all ten sub-bands. This leads to the conclusion that for the particular environment and experimental geometry, the frequency spectrum is not sufficiently wide to allow significant frequency variability which may indicate an optimum operational frequency.