Enhancing passive underwater localization with small mobile directional sensors using a source of opportunity.

A passive self-localization method is demonstrated to relatively position underwater two towed acoustic modules (TAM) located ∼1 km apart within a few meters using only a drifting source of opportunity-a broadband acoustic pinger (1.25-1.5 kHz) located 2-10 km away. Each TAM is equipped with a compact tetrahedron hydrophone array and an inertial navigation system and is controlled by an autonomous surface vehicle to provide ground truth localization. Correlation processing of these relocated TAMs' recordings yields the bearings of the source of opportunity and two low-frequency 200-300 Hz bottom-moored sources located in the sound fixing and ranging channel at ranges up to 178 km away.