An Accurate Search and Rescue Location System

Joseph H. Zablotney, Dennis D. Husch, Kerry M. Rowe, Joseph Discenza

Abstract:	This paper describes an accurate, inexpensive distress signal location system that supports search and rescue operations. Many distress signals are from vessels that have no position- finding equipment. The system described here locates these signals using a combination of direction finding (DF) and time-difference-of-arrival (TDOA) information derived from transmissions from standard marine or citizen band radios. The system consists of receivers situated around the periphery of a harbor to detect the transmitted signal. Inexpensive off-the-shelf units are used to intercept the emergency transmission, and each receiving site is configured so that the probability of intercept is high. When a distress signal is received, the direction to the transmission is measured from at least two sites to provide an initial fix. Additionally, at all receiving sites, the signal is demodulated, digitized, and immediately passed via phone line or radio frequency (RF) link to a master station. The data from each station is cross- correlated with the others to determine TDOA of the distress signal between receiver locations. Transmissions are time tagged and synchronized using a rubidium or cesium standard updated by GPS time data. A refined position is calculated from the TDOA measurements. This paper explores both the operational and performance characteristics of the system. Subjects include: (1) the differences between the DF and TDOA location methodologies; (2) the operation of the system in an environment of many signals; and (3) the quality of the fix based upon measurement data. Other than the obvious benefit of saving lives in search and rescue missions, the system will help reduce the cost of search and rescue efforts and help identify and apprehend abusers of the search and rescue system.
Published in:	Proceedings of the 47th Annual Meeting of The Institute of Navigation (1991) June 10 - 12, 1991 Williamsburg Hilton and National Conference Center Williamsburg, VA
Pages:	459 - 467
Cite this article:	Zablotney, Joseph H., Husch, Dennis D., Rowe, Kerry M., Discenza, Joseph, "An Accurate Search and Rescue Location System," Proceedings of the 47th Annual Meeting of The Institute of Navigation (1991), Williamsburg, VA, June 1991, pp. 459-467.
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