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

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 electronics-countermeasures 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.