Wide-band target depth estimation in a scattering ocean environment

This paper concerns target depth estimation using wideband active sonar multipath returns. Detailed full-field modeling of target returns is complicated by spectral amplitude and phase distortions induced by unknown target scattering, uncertainty in the bulk group delay, and unmodeled propagation effects. However, since the relative delays of the multipath return are relatively robust to modeling errors, the approach considered in this work consists of estimating a subset of the relative delays present in the data and using them with a depth-dependent likelihood function derived from ray-traces based on the ocean environment. This maximum-likelihood depth estimate (MLDE) algorithm is compared with an alternative full-field matched-field depth estimate (MFDE) approach in terms of results obtained with a real mid-frequency active sonar.