GPS Measurement Corrections for Geophysicists

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0317973LarsonFunds from this grant will support a graduate student at the University of Colorado and limited PI salary support over a two year period to conduct controlled measurements of global positioning system (GPS) pseudorange systematic errors for a variety of commercially available dual frequency geodetic GPS receivers. Unexplained and observed differences in the pseudoranges between available dual frequency GPS receivers are known to exist from previous zero-baseline measurements where a single antenna was used and the satellite signal was subsequently split and sent to two or more GPS receivers for redundant signal processing. Such biases are likely a result of a combination of biases imparted by the transmitting satellite, environmental factors and timing but also may result from specific GPS receivers use of differing observables on one or the other of the currently available GPS satellite frequencies. The situation will get more complicated in the future as the result of DOD plans to add another frequency (L5) and an additional civilian code on the existing L2 frequency. In this project, the PI and student will conduct further zero-baseline experiments to examine pseudorange biases of multiple GPS receivers under controlled temperature conditions using a thermal isolation chamber and for longer time periods than have been made to date. Results of tests of several GPS receivers available through the UNAVCO, Inc. GPS receiver pool will be compared to a single reference GPS receiver which will remain in operation for all experiments. The results should provide for improved algorithms for high accuracy and ultra precise GPS crustal motion estimates as well as improved GPS-navigation. Other broader impacts include improved confidence in sub-cm GPS estimates of position and baseline lengths for large GPS networks projects already funded by NSF and other government agencies (e.g., the southern California Integrated GPS network, the EarthScope Plate Boundary Observatory and the International GPS Service). ***