Maintaining high accuracy GPS positioning `on the fly´

A series of airborne GPS (Global Positioning System) tests using the Ashtech XII receivers was used to demonstrate the effect of cycle slips and erroneous data on the positioning accuracy. The overall achievable accuracy is in the order 20 cm; however, errors of several decimeters were detected in some instances. Traverse closures and residual analysis are used to assess the occurrence and magnitude of these errors. The addition of an inertial navigation system in the aircraft, which provides accurate relative positions, is also used to detect cycle slips and outliers in the GPS data. Strategies to achieve consistent accuracies are discussed, and results for different alternatives are presented