Environmentally tolerant waveguide-invariant target depth classification for active sonar

Shallow-water environments produce active sonar returns with many target-like returns from bottom clutter. Scatterer depth classification methods which can discriminate bottom clutter from water column targets are thus critical for controlling false alarms. In recent work, the waveguide invariant (WI) property of shallow-water channels has been used to obtain multiple snapshots of frequency-domain target return data from a single active sonar ping. These snapshots are, in turn, used to estimate a waveguide invariant spectral density matrix (WI-SDM), which can serve as a basis for depth classification. One method employing the WI-SDM performs minimum variance filtering (MVF) matched to depth-dependent signal replicas derived from a normal mode model. While MVF is capable of depth classification when the environment is known, it is sensitive to mismatch when the channel parameters are uncertain. In this paper, robustness of the WI MVF to mismatch is achieved by using environmental perturbation constraints derived from a WI-SDM for the signal averaged over the uncertain channel parameters. Simulated and real data results are presented from the CLUTTER-09 experiment in the Mediterranean Sea. [Work sponsored by ONR.]