Hydroacoustic Positioning

Hydroacoustic positioning fixes the location of an underwater asset by measuring acoustic travel times between transponders, since radio and GNSS signals do not propagate in water. Ultra-short baseline (USBL) measures range and bearing from a single hull-mounted array to a seabed or vehicle beacon; long baseline (LBL) trilaterates against an array of seabed transponders surveyed in beforehand; short baseline (SBL) uses hull-mounted hydrophones spread across the ship. Accuracy ranges from sub-meter LBL to a depth-dependent fraction of slant range for USBL, and it positions ROVs, AUVs, and divers when surface GNSS is tied to the array.