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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.