Development and Testing of Augmentations of Continuously-Operating GPS Networks to Improve Their Spatial and Temporal Resolution

Abstract

Continuously-operating networks of GPS receivers (CGPS) are not capable of determining the characteristics of crustal deformation at the fine temporal or spatial scales required. Four ‘temporal densification schemes’ and two 'spatial densification schemes' to augment the CGPS networks have been developed and tested. The four ‘temporal densification schemes’ are based on the high rate Real-Time Kinematic (RTK) GPS technique, GPS multipath effects, Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR). The 'serial scheme' based on using GPS as a seismometer has been proposed. Simulated seismic signals have been extracted from the very noisy high rate RTK-GPS results using an adaptive filter based on the least-mean-square algorithm. They are in very good agreement with those of the collocated seismometers. This scheme can improve the CGPS temporal resolution to 0.1 second. The 'retro-active scheme' takes advantage of the fact that the GPS multipath disturbance is repeated between consecutive days. It can therefore provide a means of correcting multipath errors in the observation data themselves. A reduction of the standard deviations of the pseudo-range and carrier phase multipath time series to about one fourth and one half the original values respectively, has been demonstrated. The 'all-GPS parallel scheme' uses the multipath effects as a signal to monitor the antenna environment. Models relating the changes of multipath and antenna environment have been derived. The 'cross-technique parallel scheme' integrates the collocated CGPS, VLBI and SLR results, taking advantage of the decorrelation among their biases and errors. Crustal displacement signature has been extracted as a common-mode signal using data from two stations: Matera in Italy and Wettzell in Germany. Two 'spatial densification schemes' which can verify with each other have been developed and tested. The 'soft' scheme integrates CGPS with radar interferometry (InSAR). The Double Interpolation and Double Prediction (DIDP) approach combines the strengths of the high temporal resolution of CGPS and the high spatial resolution possible with the InSAR technique. This scheme can improve the spatial resolution to about 25m. The 'hard' scheme requires the deployment of single-frequency receivers to in-fill the present CGPS arrays. Alternatively some receivers may be installed at some geophysically strategic sites outside existing CGPS arrays. The former has been tested within Japan's GEONET, while the latter has been tested using a five-station array.