False-Alarm Reduction for Low-Frequency Active Sonar With BPSK Pulses: Experimental Results

In the last two decades, low-frequency active sonar (LFAS) emerged as one of the most efficient tools for shallow-water antisubmarine warfare (ASW). Like any long-range active sonar system, LFAS produces a large amount of unwanted sea bottom echoes or clutter. These echoes give way to false alarms that increase the computational load of target trackers and delay the correct classification of each echo. The number of false alarms due to clutter can be reduced either through echo classification techniques or through Doppler filtering provided the targets of interest have a nonzero radial velocity. Much research has been carried out on waveform investigation for the efficient use of bandwidth capabilities of modern sonar transmitters. Among the quantity of waveforms, binary phase-shift keyed (BPSK) pulses have emerged as exhibiting cross-correlation properties relevant to Doppler filtering while maintaining a range resolution comparable to frequency-modulated (FM) pulses. In this paper, we have successfully applied a false-alarm reduction technique using contacts obtained with an FM pulse subsequently processed by Doppler filtering with a BPSK pulse. The Doppler filtering performance for this pulse is evaluated on an experimental data set and a few limitations of BPSK are identified.