A codeless, real-time, high-accuracy NAVSTAR-GPS positioning system is under development for the offshore environment. The Marine Positioning Sensor (MPS-l) accuracy goal is 2 m CEP (5 m 2drms) out to distances of 500 km. Allowable marine vessel velocities are up to approximately 10 knots. Differential operation cancels effects of DoD-induced dither of the NAVSTAR signals, and dual Ll- and L2-band codeless operation provides for calibration of ionospheres delay effects.
A new technology whose first commercial application is in land surveying is now being applied to marine positioning and navigation as a civil use of the Department of Defense (000) NAVSTAR Global Positioning System (GPS).
This technology, named SERIES (Satellite Emission Range Inferred Earth Surveying), can do precision positioning with NAVSTARGPS signals with no knowledge of their secret codes, i.e., it is codeless. Because of this capability, SERIES technology circumvents the potentially serious security problem posed by civilian NAVSTARGPS P-code correlating receiver systems as discussed by Booda (1984).
SERIES was conceived and demonstrated at the California Institute of Technology, Jet Pro pu1s ion Lab 0 r a to r y (J PL), with fun din g from the National Aeronautics and Space Administration (NASA). The SERIES technology in its current configuration of codeless pseudo-ranging was developed in 1980 (MacDoran, Spitzmesser and Buennagel, 1982), but its roots began in 1975 with a purity interferometer approach (MacDoran, 1979). The SERIES invention was originally intended for highly precise measurements of the earth's crust in a search for crustal deformation patterns that could be used for tectonic studies and earthquake prediction. MacDoran discovered that signals from earth-orbiting satellites, especially the NAVSTAR satellites, could be used with no knowledge of the P or CiA codes, opening the door for use 0 f the technique in a wide array of commercial and scientific applications. MacDoran has been granted the waiver of commercial rights to the invention by Caltech and NASA. The SERIES invention is a method and apparatus (equipment and processing software) that provides three-dimensional relative position -latitude, longitude, and height with accuracy of a few centimeters if required. This accuracy is perhaps 1,000 times the level intended by the NAVSTAR-GPS.
ISTAC is an "equal opportunity radio signal consumer" because ISTAC will be able to use the radio illumination provided by satellite television transmissions or even the Soviet Union's global navigation satellite system (GLONASS) should the NAVSTAR satellites be unavailable for some unknown reason. However, the NAVSTAR satellites are clearly the radio illuminations of choice because of the excellent geometry and atomically stabi1ized radiofrequency transmissions. For a complete discussion of the NAVSTAR Global Positioning System, the reader is referred to Parkinson and Gilbert (1983).
