Evaluation of Real-Time, Long-Range, Precise, Differential, Kinematic GPS Using Broadcast Orbits

O.L. Colombo, A.W. Sutter, A.G. Evans

Abstract:	A kinematic, differential GPS real-time navigation system is being developed at the NSWCDD research establishment of the US Navy in Dahlgren, Virginia. The immediate objective is to achieve highly precise geolocation of ground objects using an advanced digital airborne camera flown at great distances from the nearest GPS ground station. Here the kinematic solution is used to locate and orient precisely the camera in space, by updating an inertial navigation unit attached to the camera. The main GPS data are the double-differenced, ionosphere-free combination of the L1 and L2 carrier-phases, or Lc. The real-time system has two major components. The first one, data retrieval, is for collecting, transmitting, and making available for analysis the receiver data from the vehicle and from the sites of a network of reference stations. The other component, data processing and navigation, is for editing, correcting and analyzing the data to obtain the precise position of the vehicle with a minimum of delay. The approach followed in this work is to double-difference the receiver data, and to use the Navigation Message broadcast satellite ephemerides, while estimating their errors. The system's real-time position accuracy has been evaluated using data from different test data sets, including two aircraft flights. The trajectories calculated with the real-time navigation Kalman filter are compared to precise solutions, relative to a nearby receiver, with correctly fixed carrier phase ambiguities. Early results indicate that decimeter-level positioning at more than 1000km from the nearest base station can be achieved in real time, once the filter has converged sufficiently, and that this accuracy can then be maintained over many hours.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	2622 - 2630
Cite this article:	Colombo, O.L., Sutter, A.W., Evans, A.G., "Evaluation of Real-Time, Long-Range, Precise, Differential, Kinematic GPS Using Broadcast Orbits," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 2622-2630.
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