Improving the precision of high‐rate GPS

In order to improve the accuracy of high‐rate (1 Hz) displacements for geophysical applications such as seismology it is important to reduce systematic errors at seismic frequencies. One such GPS error source that overlaps with seismic frequencies and is not currently modeled is multipath. This study investigates the frequencies and repetition of multipath in high‐rate GPS time series in order to maximize the effectiveness of techniques relying upon the geometric repeatability of GPS satellite orbits. The implementation of the aspect repeat time adjustment (ARTA) method described here uses GPS position time series to estimate time‐varying and site‐dependent shifts. As demonstrated for high‐rate GPS sites in southern California this technique significantly reduces positioning noise at periods from 20 to 1000 s. For a 12‐hour time series, ARTA methods improve the standard deviation of the north component from 8.2 to 5.1 mm and the east component from 6.3 to 4.0 mm. After applying ARTA corrections, common mode errors are removed by stacking. This method further improves the standard deviations to 3.0 and 2.6 mm for the north and east components, respectively.