GPS (Global Positioning System) navigation systems include a constellation of satellites each of which provides a coded signal which may be picked up by radio receivers on the surface of the earth. Separate coded signals from a set of satellites may be processed by a receiver system for use in determining location as defined by latitude, and longitude based on the code carried by the signals. The operation of GPS systems in determining location based on coded signals received from satellites reflects the conventional functioning of such systems.
However, it has been found that the signals generated by GPS satellites may be used in other ways and in particular the carrier phase of the signals may be used in certain surveying applications. For example, a pair of stationary antenna/receiver combinations may be located at the ends of a baseline (whose length is required to be determined) and, based on the observed relative phase of the GPS carrier signal from satellites at known positions, determine the orientation of the antenna pair relative to an earth reference.
Current GPS orientation techniques require two position measurements either accomplished using two antennas and two receivers as typical in surveying applications or requiring precise movement of a single antenna/receiver pair to two different relative positions. These approaches typically require significant separation (>1 meter) between measurements in order to mitigate position inaccuracy between measurements making for large, bulky equipment.
Digital magnetic compasses are currently used in handheld target systems to determine orientation relative to north. These devices may be easily influenced by local fields due to geological formations, metal vehicles and even equipment worn by the user. There is generally no indication when these devices are compromised leading to incorrect targeting solutions. GPS solutions are generally discounted as they can be influenced by multipath effects or jamming.
A need therefore exists for compact GPS, non-magnetic sensing of azimuth direction for target systems.