OFDM for Underwater Acoustic Communications

Chapter 19Underwater Ranging and Localization

Underwater localization is a topic of great interest and study, and application demands drive the need for better and better solutions. Several current systems feature augmented inertial navigation methods, which use filtering and tracking methods to provide corrections and improvements upon traditional onboard navigational equipments [158, 231]. Aside from these methods, there are several localization techniques based on acoustic signaling.

• Long baseline (LBL) system. Several transponders are installed at the sea floor, and an underwater vehicle interrogates the transponders for round-trip delay estimation followed by triangulation [370]. LBL has good localization accuracy, but it requires long-time calibration.
• Short baseline (SBL) system. A series of closely spaced receivers can be installed on a platform such as a surface ship to monitor the incoming signals from an underwater emitter. The time differences of arrivals (TDoAs) are used for localization.
• Ultra-short-baseline (USBL) system. A small array of hydrophones is used to estimate the angle of arrival (AoA) of the incoming signal from an underwater emitter. The AoA information is combined with a range estimate for much improved localization performance than SBL systems.
• Floating buoy based system. This system acts like a long base line system except that the reference points are surface buoys. There are commercial products—the GPS Intelligent Buoys (GIB)—that route signals ...