Comparison of transmission loss for underwater sound pulses measured using matched filters and integrated received power

Abstract

Transmission loss (TL) may be found from the amplitude of a matched filter correlation applied to a pulsed acoustical signal. Use of matched filters to determine TL is advantageous because the technique can be applied continuously in real time without previously determining the pulse arrival time. However, distortion of the transmitted waveform by scattering, multiple path propagation, and Doppler frequency shift reduces the amplitude of the matched filter output thus increasing the TL determined in this way. The conventional TL calculation involves filtering the signal and integrating the received power for the duration of the pulse which yields a TL based on total received energy. This method must be applied after data is collected because the time of arrival of the pulses must first be determined. TL measurements derived using both methods were compared for data gathered during two trials in the Gulf of Mexico in both shallow and deep water environments. The transmitted waveforms were linear frequency-modulated pulses with a frequency range of 10 Hz, centered at 1055, 1225, and 1395 Hz. Results of the comparison will be presented.