See current research theme 'Algorithms & Software'

Using Single-Frequency GPS Receivers to Densify Continuous Monitoring Systems for Geodynamic Applications

Researchers have extensively used GPS measurements to study crustal motion for more than a decade. In general the methodology has been to establish special deformation networks, and to measure these on a campaign basis on a regular basis (typically annually). The data is then processed using scientific GPS software (such as the Bernese GPS Software Package, developed at the University of Bern, Switzerland; GAMIT, developed at MIT and Scripps Institute of Oceanography; and others) to determine the average crustal motions. This GPS geodesy technique can determine baseline solutions to accuracies of 0.01ppm or better. To achieve finer temporal resolution of crustal motion the focus is shifting to continuous and automated GPS monitoring systems. Examples of such networks include the Japanese nationwide GPS network, the Southern California Integrated GPS Network, and the network operated by the Institute of Earth Sciences Academia Sinica in Taiwan.

However, these permanent arrays may provide the basic infrastructure for other precise GPS techniques. A methodology is being investigated at SNAP by which a specially modified version of the Bernese GPS Software Package processes permanent GPS station data, in order to generate empirical corrections which may be applied to the double-differenced data of any GPS baseline located within an area enclosed by the permanent GPS stations (see figure below). These corrections have the effect of improving baseline solution accuracy by up to an order of magnitude, even for baselines ranging up to 100km in length, and can be used to support kinematic, rapid static and continuous positioning applications. Significant additional advantages are obtained: the baselines may be observed using low-cost, single-frequency GPS receivers, the observation sessions may be comparatively short (similar to those used for "rapid static" GPS surveying techniques), and it is possible to implement such schemes in real-time (as used in the Singapore multi-base station project). Such a scenario was part of SNAP's research into 'low-cost' GPS surveying systems.

This combination of a few external permanent, "fiducial" GPS stations surrounding a temporary GPS network, offers considerable flexibility and cost savings for geodynamic applications which require a dense spatial coverage of GPS stations, and where it is not possible, nor appropriate, to establish permanent GPS networks. Download a PDF file giving further information on this project

Tests have been carried out using data collected in Taiwan, U.S., Singapore and Japan. This is the strategy that was implemented for the second generation volcano monitoring project.

Initially a modified version of the Bernese GPS Software Package was used for these studies. A new GPS network processing 'engine', developed in the C programming language, that is able to access and process multiple GPS reference station data in real-time was subsequently developed as part of the Singapore multi-base station project referred to earlier. Studies have also been made concerning integrated GPS/GLONASS networks.

Integrated network design; outer network of permanent dual-frequency GPS receivers (AFS), with inner network consisting of a large number of "slave" GPS receivers (ASS) which may be static or in motion.