Long baseline
Long Baseline (LBL) is an underwater navigation system based on waterborne sound. For this purpose, several hydrophones are deposited at defined positions on the sea floor , a so-called array. The object whose position is to be determined (usually an AUV ) also has a transmit / receive hydrophone. It sends a signal to the hydrophone array on the ocean floor. The hydrophones answer. The distances are calculated from the transit times between sending the first and receiving the second signal.
Because of the great effort involved in deploying the hydrophones and positioning them on the seabed, the system for positioning objects floating on the surface, such as research vessels or drilling platforms, has now been completely replaced by satellite navigation . Compared to the less complex USBL method, LBL has the advantage of higher accuracy.