Two-Pass Continuous Active Sonar Processing

Sonar systems using Linear Frequency Modulated (LFM) Continuous Active Sonar (CAS) waveforms can provide a higher target update rate than conventional Pulsed Active Sonar (PAS) waveforms through sub-pulse processing. The higher target update rate promises to improve tracking performance. The drawback of sub-pulse processing is that reducing the duration and bandwidth of the processed waveform decreases the Signal-to-Noise Ratio (SNR) or Signal-to-Reverberation Ratio (SRR) of the target echoes. Previous work suggests that incoherently averaging CAS sub-pulses can exploit the range-Doppler bias to make an estimate of the target Doppler as well as improve overall detection performance. The drawback of this technique is that the higher target update rate of the CAS waveform is not exploited for tracking. Here a two pass approach is presented that both retains the higher target update rate while simultaneously removing the range-Doppler bias. Results using this two-pass approach will be shown using the Littoral Continuous Active Sonar 2016 sea trial (LCAS16).