Low-Cost Deformation Measurement System for Volcano Monitoring

Ground deformation due to volcanic magma intrusion is recognised as an important precursor of eruptive activity at a volcano. The Global Positioning System (GPS) is ideally suited for this application. With the advent of inexpensive GPS receiver boards, the development of a low-cost GPS-based volcano monitoring system is now possible. It provides an expendable way of measuring volcanic activity. This paper presents a novel, autonomous, deformation monitoring system based on the use of the low-cost Novatel Superstar II receiver. The system uses several of those GPS units, one of which being at a known reference location and the others being scattered around the area of interest. The GPS Superstar II receivers provide measurements of the L1 carrier phase and of the GPS ephemeris. Those measurements are logged at a user-defined sampling rate, and transmitted via a radio link to a central processing station. The post-processing engine uses those data in ambiguity resolution and baseline computation algorithms. The measurement of changes in GPS baseline easting, northing and height components over time forms the basis for measuring the volcano's expansion prior to eruption.
The paper reviews the major practical design considerations for GPS-based volcano monitoring systems, together with the dominant error sources. The data processing steps necessary to obtain the baseline between the reference receiver and each slave unit is also detailed. The system validation is presented, showing the performance results obtained for several baseline lengths, data sampling rates and observation session lengths. Each hardware and software component is described, as well as the system architecture and the special challenges in deploying and operating such a system in an inhospitable environment.