Abstract
Flight experiments of the differential GPS (DGPS) navigation system were conducted by NAL (National Aerospace Laboratory). The purpose of the experiments was to evaluate the performance of the DGPS for the terminal area operations. The Dornier-228-200 (Do-228), an experimental research aircraft of NAL, was used for the experiments. A C/A-code, 1 channel GPS receiver (Rockwell/Collins Navcore-1) was installed onboard the Do-228. As a ground reference, the identical receiver was placed at a precisely surveyed location in the airport.
In a post-flight analysis, navigation solutions were estimated by a DGPS navigation filter developed at NAL. This filter consists of a ground reference differential correction filter (DCF) and an airborne navigation filter (ANF). Differential corrections to the pseudorange and deltarange observations were caluculated and filtered by the DCF. Mesurement data obtained by the airborne receiver were differnitially corrected and processed by ANF to yield the position and velocity of the aircraft. The aircraft was tracked by a laser tracker, with subsequent data being used to provide a reference profile of the airplane.
This paper discribes the DGPS navigation system, the algorithms of the DGPS navigation filter, and the results of the post-flight analysis. DGPS mean vertical error showed a factor of 6 improvement over that of GPS, while lateral error showed a factor of 3 improvement. Since GPS was under SA (Selective Availability) during the flight experiments, effectiveness of DGPS was demonstrated.
