Permanent Automatic Low-Cost GPS Deformation Monitoring Systems: Error Mitigation Strategies and System Architecture

Chris Rizos, Shaowei Han and Craig Roberts

Abstract:	Ground deformation due to volcanic magma intrusion, crustal motion, ground subsidence, structural deformation, etc., are phenomena ideally suited for study using GPS. The change in length, height difference and orientation of baselines connecting GPS receivers in a carefully monumented ground network can be monitored. This is done by repeatedly measuring the same baseline components to an accuracy commensurate to, but preferably much higher than, the expected baseline component changes. GPS techniques based on the "campaign" principle, that is, the periodic (often annual) re-survey of a network of control points, have become the mainstay of geodetic applications such as regional geodynamic studies and local ground deformation monitoring. However, over the last half decade or so there has been a growing interest in the deployment of permanent, continuous GPS monitoring networks -- partly as a result of the realisation that continuous measurement of a deformation phenomenon, rather than its periodic measurement, has certain inherent advantages. The GSI network in Japan and the SCIGN network in California are examples of large scale, permanent GPS networks for (near-)real-time crustal motion monitoring. However, smaller scale GPS arrays such as those on the Augustine volcano (Alaska), the Popacatepetl volcano (Mexico), the Kilauea volcano (Hawaii), and the Rabaul volcano (Papua New Guinea) reflect a growing interest in localised continuous GPS volcano monitoring systems. GPS is also increasingly used to monitor engineering structures such as dams, bridges, offshore platforms, etc. The development of deformation monitoring systems is a significant engineering challenge. What hardware configuration should be used? How should the data be modelled - "kinematic" or "static"? How to address the uncertainty implicit in wireless data communications? Often the only obvious solution is to simply buy commercial "off-the-shelf" real-time-kinematic (RTK) GPS systems. This is the high cost option as it involves dual-frequency GPS instrumentation originally "packaged" to measure a single baseline in real-time, on a single epoch basis. However, there are several hundred active volcanoes in the world, many located in the less developed countries, and the cost of GPS monitoring systems must be significantly reduced if the technology is to contribute to volcanic hazard mitigation. Furthermore, to adequately "map" the complex deformation field, many GPS receivers -- perhaps 10 or more -- would be required. The only alternative is therefore to develop a low-cost option based on single-frequency GPS receivers. This paper describes the data processing strategy and system architecture of The University of New South Wales system. The proposed system consists of two distinct networks: (a) a local, dense array of single-frequency GPS receivers that will map the deformation, (b) surrounded by a small number of sparsely distributed, dual-frequency GPS receivers. This external "fiducial" network is used to mitigate residual biases due to ionospheric and tropospheric refraction, and satellite ephemeris errors, by generating corrections to the station coordinates of the internal network. Such a configuration is expected to deliver millimetre level horizontal accuracies, and centimetre level vertical accuracy, for observation spans of the order of one hour or so. The system will be deployed for testing in 1998 or 1999.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	909 - 917
Cite this article:	Rizos, Chris, Han, Shaowei, Roberts, Craig, "Permanent Automatic Low-Cost GPS Deformation Monitoring Systems: Error Mitigation Strategies and System Architecture," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 909-917.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In