Codeless GPS Systems for Positioning of Offshore Platforms and 3D Seismic Surveys

P. F. MacDoran, R. B. Miller, L. A. Buennagel, H. F. Fliegel, L. Tanida

Abstract:	A technique known as SERIES {Satellite Emission Range Inferred Earth Surveying), ,is a method by which radio signals from artificial satellites already in Earth orbit can be exploited for positioning and navigation. The existing satellites of choice are those of the Global Positioning System (GPS)The SERIES technique makes it possible to perform simultaneous pseudo ranging to multiple NAVSTAR-GPS satellites without knowledge of the codes usually required to make use of these satellites .. The accuracy achievable with the SERIES system in a dynamic environment is at the meter level when operated in a differential mode with a single base station ,which.may be several hundred km away. To achieve real time operation, it is necessary to cross-link the base station receiver output to the dynamic vessel which determines its position and velocity relative to the geodetic position of the base. The demands upon the cross-link communications are very modest at an average rate of only one byte per second. Since the technique has no requirement for a knowledge of the GPS codes, it is possible to use both of the P-code channels at L1 and L2 to accomplish the ionospheric calibrations which are essential for achieving one meter accuracy over distances of several hundred kilometers. The conditions under which the SERIES technique will function are compatible with all civilian needs but are not useful in military operations because of electronicscountermeasures already developed. By the use of a pair of receivers on a single vessel, it is possible to configure an angular orientation measurement system using the NAVSTAR satellites as the frame of reference and with an accuracy of 0.1 degree or better without any moving parts. SERIES feasibility demonstration equipment has been developed and sub-meter dimensional accuracy has been demonstrated. Early applications of the techniques will be for the positioning of offshore platforms and for vessels engaged in 30 seismic surveys. For 30 seismic surveys, both the boat and seismic streamer tail buoy will be positioned relative to each other with meter level accuracy and tied back to a shore based reference with similar accuracy. From its beginnings, NAVSTAR-GPS seemed to hold significant promise for high precision civilian applications. However, the perceived necessity to access the range codes and encrypted telemetry used to secure the system from potential hostile use against the U.S., has thwarted any serious civil commitments for NAVSTAR utilization. ISTAC, Inc. has an alternative utilization which needs no codes and offers the possibility of a service completely independent of military activity.
Published in:	Proceedings of the 1984 National Technical Meeting of The Institute of Navigation January 17 - 19, 1984 San Diego, CA
Pages:	39 - 37
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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