Range Estimation of Snapping Shrimp Sounds Using TDOA Structures and a Multilayer Perceptron

This study proposes a TDOA-MLP method for estimating the range of snapping shrimp sources from the array-wide time-difference-of-arrival (TDOA) structure measured by a vertical line array. BELLHOP arrival-time replicas were generated for the SAVEX15 environment by varying source range, array tilt, and maximum water depth, and a multilayer perceptron was trained to estimate source range with array tilt as an auxiliary output. To provide a more stringent assessment of range generalization, six continuous source-range intervals were excluded from training, and only their inner portions were used for blocked-holdout evaluation, providing an approximately 2-m separation from the nearest training ranges. The resulting overall range-estimation mean absolute error (MAE) and root mean square error (RMSE) were 0.864 and 1.056 m, respectively, with regional MAEs of 0.762, 0.728, and 1.119 m for the near-, mid-, and far-range regions. Additional analyses showed that the estimation error increased with controlled arrival-time perturbations and varied with the maximum-depth condition. When applied to experimental SAVEX15 snapping shrimp data, the TDOA-MLP produced range distributions and snap-to-snap variations generally consistent with those obtained using template matching, steered frequency-wavenumber analysis, and frequency-difference matched-field processing. Relative to template matching, the mean absolute relative range difference was 4.54%. Because ground-truth source ranges were unavailable for the experimental data, the field results demonstrate consistency among the methods rather than absolute localization accuracy. The proposed method provides a low-dimensional learning-based approach for estimating the range of impulsive snapping shrimp signals from array-wide TDOA structures.