Approaches for Using Three Dimensional Sonar as a Supplemental Sensor to GNSS

W.R. Woodward, R. Webb, R. Kahrs Hansen, B. Cunningham J.N. Markiel

Abstract:	The core of an underwater vehicle’s navigation suite is the Inertial Navigation System (INS). Using a series of sensors, the INS estimates the position of the vehicle. One of the sensors is the Global Positioning System (GPS) receiver, which provides a position fix. Typically, a series of GPS position fixes are taken just before a vehicle submerges. After that, the INS must rely on other sensors such as the fathometer, speed log, and Doppler sonar to dead reckon (DR). A high quality INS, with the absence of GPS, may offer a Circular Error Probable Rate (CEPR) of 0.1% of the Distance Traveled (TR) per hour while a less expensive INS may only offer a CEPR of 0.5% or greater. However, regular underwater position fixes could offer a Circular Error Probable (CEP) of 10- meters without surfacing or having an antenna surface to obtain a GPS position fix. New real-time 3-D sonar technology offers multiple ways to obtain underwater position fixes with the accuracy of GPS. The Echoscope 3-D sonar from CodaOctopus uses a 128 X 128 array to produce 16384 beams with each ping in real time. Each ping from the sonar generates a 3-D dataset that can be used to accurately measure the position of an underwater object relative to own ship. The geo-spatial position of the vehicle is calculated from the position of the vehicle with respect to a fixed underwater navigation aid. Three-Dimensional maps of the underwater landscape can also be developed with multiple datasets and mosaic imaging techniques. Position fixes can be obtained from static features using imaged-based navigation algorithms. The ability to obtain an underwater position fix can greatly extend the time a vehicle can stay underwater, with a CEP of 10 meters without surfacing or having an antenna surface to obtain a GPS position fix. In an environment where regular 3-D sonar position fixes can be obtained, the vehicle would not have to surface for a GPS position update. UrsaNav, working with CodaOctopus, is developing a system to provide accurate real-time underwater position fixes as a supplemental sensor to GNSS.
Published in:	Proceedings of IEEE/ION PLANS 2010 May 4 - 6, 2010 Renaissance Esmeralda Resort & Spa Indian Wells, CA
Pages:	1112 - 1117
Cite this article:	Woodward, W.R., Webb, R., Hansen, R. Kahrs, Markiel, B. Cunningham J.N., "Approaches for Using Three Dimensional Sonar as a Supplemental Sensor to GNSS," Proceedings of IEEE/ION PLANS 2010, Indian Wells, CA, May 2010, pp. 1112-1117. https://doi.org/10.1109/PLANS.2010.5507197
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