A set of advanced broadband processing algorithms and a broadband classifier are being proposed for clutter rejection and detection/classification of weak targets in sonobuoy returns. Novel algorithms for the harsh shallow water acoustic environment are needed since the threat model for the ASW has shifted from deep to shallow water. Recent efforts by the underwater community have identified the advantages of using broadband signals and new processing techniques to limit the effects of reverberation. This effort proposes an unconventional approach that exploits the broadband nature of explosive or impulse-like sources, as well as the new generation of coherent broadband acoustic sources the Navy uses. This broadband approach achieves very good array gain and dynamic range using a limited number of sensors. This technique uses degrees of freedom in the frequency domain, by drawing an analogy with degrees of freedom in space in a discrete line-array. The algorithms being proposed include broadband adaptive filtering, beam canceling and modified eigen-vector beamforming techniques. These algorithms are used to feed a broadband classifier based on a time/frequency wavelet analysis, and are expected to enhance the performance of future ASW systems operating in high clutter environments.
Benefits: Broadband processing based sensors are becoming more and more appealing because they are compatible with low-cost, small-size systems. The technology trend for the next century both in underwater and air acoustics is shifting to the use of broadband rather than narrow band signals. Even if broadband processing is associated with increased computing requirements, we have reached the point today where computing power is no longer the limitation. Commercial applications for this technology are broad since these algorithms could be applied to any sonar bistatic and monostatic or acoustic array that must work in a cluttered environment (depth profiler, fish finders, sub-layers characterization in shallow water for the petroleum industry, and seismic sensors).
Keywords: Broadband Signal Processing Adaptive Beam Canceling Broadband Adaptive Beamforming ASW Clutter rejection Low-cost Small-size Sparse Arrays Broadband Classifier
