Rapid static and kinematic global positioning system solutions using the ambiguity function technique


  • Gerald L. Mader


This paper describes an ambiguity function technique by which phase data from the Global Positioning System (GPS) maybe used to obtain survey positions for monuments occupied using a suitable GPS receiver. The principal benefit of the technique is the speed with which it may be used and its immunity to cycle slips or other discontinuities in the phase data that commonly occur. The technique uses phase measurements from satellites at both L1 and L2 frequencies from various directions in the sky. When sufficient measurements are available, the signals will destructively interfere at all but the correct location. Depending on the satellite geometry, the number of satellites in view, and the a priori knowledge of the station's position, a sufficient number of measurements may be obtained from a single monument occupation. The data collected over an occupation lasting only a few minutes maybe averaged to a single value at a particular epoch. Equivalently, the data collected at only a single epoch may also be used. The ability of the technique to work with data from a single epoch allows the integer ambiguities on moving platforms to also be determined. This will greatly enhance the practical operation of kinematic GPS for a variety of remote sensing applications. A computer program employing this ambiguity function technique has been written and used to process static as well as kinematic data. The results indicate horizontal precisions and accuracies of 1 cm or better and vertical precisions and accuracies of 1 to 3 cm. The data processing requires no data editing, is easy to use, and can be operated without any specialized knowledge of kinematic GPS techniques. The correction for the effects of the ionosphere are also demonstrated at distances up to 250 km. The use of the ambiguity function for geophysical monitoring and kinematic remote sensing applications appears limited in distance only by the accuracy of the GPS orbits. The utility of the ambiguity function for rapid static surveying and on-the-fly bias fixing out to distances of several hundred kilometers appears practical.