Broadband Doppler-Sensitive Waveforms for Energy-Constrained Distributed Active Sonar Systems

The Doppler cue obtained from using narrowband Doppler-sensitive sonar waveforms is an effective discriminator of moving targets from clutter. Often, however, targets will exhibit low Doppler, caused by slow-moving or cross-range motion, with Doppler further reduced in multistatic sonar for targets between source and receiver. Moreover, the strategically important littoral conditions exhibit increased reverberation levels over longer ranges, masking low Doppler targets. The classic way to manage the low Doppler target is to transmit a Doppler insensitive broadband waveform, which gives improved range resolution, enhancing target discrimination in high reverberation regions. Unfortunately, broadband Doppler-insensitive waveforms are difficult to discriminate from bottom clutter, often resulting in high numbers of false alarms. Simultaneous transmission of the two waveforms is not favorable, diminishing the lifetime of battery-operated sources. Broadband Doppler-sensitive waveforms have been discussed in the literature for several decades, and have been shown in theory to provide discrimination in both Doppler and range. In order to effectively use these waveforms, however, the sonar processing must be optimized accordingly. We propose to use our previous experience modifying AN/SQS-53C sonar signal processing algorithms for broadband Doppler-sensitive waveforms to provide innovative algorithms that will account for the unique problems and opportunities presented by the waveforms.