THE USE OF AIRBORNE DIFFERENTIAL GPS TO DETECT COORDINATE AND CALIBRATION ERRORS IN DME NAVIGATION AIDS

In May 1993, in support of Eurocontrol's WGS 84 Implementation Program me, a project was undertaken to assess the accuracy of navigation aid coordinates. The exercise involved flying a route over a number of Eur opean countries, in an aircraft which was equipped for multi-DME 'data puddle' position updating, and which also carried Global Positioning System (GPS) receivers. This test flight, carried out under contract t o Eurocontrol, involved two parties, namely the Defence Research Agenc y (DRA) Bedford, who provided the airborne trials facility and DME dat a, and the Institute of Engineering Surveying and Space Geodesy (IESSG ) at the University of Nottingham, who provided an analysis of the DME coordinate accuracy. The aim of this test flight was to assess whethe r it is possible to determine independently the (WGS 84) coordinates o f DME ground stations from the air, by using the same DME range measur ements which are used to update aircraft position information in-fligh t. The procedure used to determine DME coordinates involves reversing the position updating principle. Instead of taking the DME ground stat ion coordinates as known points and using the DME range measurements t o determine the aircraft's position, the aircraft's position is indepe ndently determined (from DGPS) and the range measurements are used to estimate the coordinates of the DME ground stations.