GPS Network Design and Error Mitigation for Real-Time Continuous Array Monitoring Systems

In this paper a near real-time (typically a baseline update once per hour, or once per day) continuous array system, with at least three dual-frequency GPS receivers connected to the IGS network, and many single frequency receivers, is proposed for monitoring applications covering a region of 50km radius. A weighted differential GPS method, appropriate for the suggested array design, can be implemented in order to eliminate or mitigate the orbit bias, including the effects of SA. A local area epoch-by-epoch and satellite-by-satellite ionospheric delay model, determined using dual-frequency observations, is used to correct single frequency observations. Tropospheric delay is taken into account by modelling it as a first order Gauss-Markov (or random walk) process with temporal correlations. Multipath elimination is achieved by using an Finite Impulse Response (FIR) lowpass filter for the local ionospheric delay model, and multipath extraction using an FIR bandpass filter to account for the multipath in real-time. The biases dependent on the GPS receiver and antenna are also discussed and associated optimal network designs for data processing are suggested. In addition, efficient and reliable ambiguity resolution, and automatic cycle slip detection and repair procedures will be incorporated. This system would be capable of millimeter horizontal accuracy and centimeter vertical accuracy, and is intended to address real-time applications for earthquake studies, and for volcano and engineering deformation monitoring. INTRODUCTION GPS continuous network array systems have been established in support of crustal deformation monitoring studies, such as in southern California, Japan, Vancouver Island in Canada (Bock & Shimada, 1989; Chen, 1994). They will provide invaluable data for understanding and modeling the GPS error spectrum over a wide range of spatial and temporal scales, and enable us to characterize and understand the spatial distribution and time dependence of deformation within tectonic regions, from which constraints on the physics of the deformation process can be inferred. However, the main emphasis for such systems is rapid and automatic data post-processing. A recent Australian Research Council project to develop an automatic GPS array system for deployment at active volcano sites is mostly concerned with real-time data processing and deformation analysis for a local area (say, within a region of 50km radius); a critical issue if a catastrophic failure is imminent (Rizos et al, 1996). This kind of development work has received some attention