Nonlinear signal processing techniques for active sonar localization in the shallow ocean with significant environmental uncertainty and reverberation

Sonar signal processing techniques based on acoustic models of shallow ocean environments are frequently of limited use for the mid-to high-frequency regimes typical for active sonar.To make use of acoustical models of the environment, signal processing algorithms typically require better-than-a-wavelength accuracy in the acoustic path estimates.Given this limitation, and practical knowledge that can be expected for shallow ocean environments, model-based signal processing schemes are often limited to frequencies below approximately 1 kHz.This frequency limitation is overcome by extending a recent passive source localization technique (frequency difference matched field processing, see Worthmann et al., JASA 138, 3549-3562, 2015) to monostatic active sonar target localization, where strongly reverberant environments can obscure a desired target echo.The frequency difference active sonar technique is presented along with comparisons to existing detection and localization algorithms.Additionally, simulations are provided of these algorithms' performance in a 200-m deep ideal waveguide with strong reverberation and environmental uncertainties that includes a mid-water-column target at 5-km range, using broadcast frequencies between 2 kHz and 5 kHz.Successful detection and localization of this target using this nonlinear frequency difference scheme is found to be possible at signal-to-reverberation levels as low as -12 dB in this simulation.