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Some Post Processing Results using Carrier-Phase GPS Data

These are some results obtained by post-processing carrier phase data from a pair of Motorola Oncore VP GPS receivers. The plot shows the baseline vector between two receivers that were about 3.5 km apart.

The vector was computed every 30 seconds for a run lasting about 1/2 hour. At each 30-second interval the integer ambiquity was estimated (using the LAMDBA method published by P. de Jonge and C. Tiberius at the Delft University of Technology) and the baseline vector was calculated.

The successive positions typically differ by 100 microns or less (over 3 km baseline!) and during the 1/2 hour run the position drifted 2-3 mm. This slow drift may be due to multipath or incomplete cancellation of ionospheric effects. The data were recorded at the ranch of a friend (N7ZT) in the basin & range country of Nevada, and both receivers were in separate shallow canyons. No special precautions were made to avoid multipath reflections (e.g. no choke ring mounts for the simple Motorola patch antennas).

The data were used to establish his property lines so he could put up a fence to keep his neighbors cows off his land. The accuracy of the data appears to be sufficient for the purpose.