Strategic Planning Tool for GPS Surveys

Accuracy of a GPS baseline determination is a complex function of satellites selected and the duration and timing of the data collection interval. Satellite selection can be extremely important if the GPS receiver employed is one that tracks only four satellites simultaneously. Even with receivers that track all visible satellites, the timing and duration of the data collection interval can be significant. For short data collection intervals and short baseline observations, an order of magnitude difference in accuracy may result, depending on whether or not the whole cycle ambiguity can be resolved. The ability to resolve whole cycle ambiguities is in turn determined by which satellites are selected and the timing and duration of the tracking interval. Magnavox has developed a "Differential GDOP" program that provides a measure of the ability to resolve whole cycle ambiguities as a function of these parameters. This paper describes a method and rationale for "Differential GDOP" computations. A practical example is used to illustrate its benefits in generating a data collection strategy.