GPS system: remote data breakthrough
In 1998 a group of scientists at the Australian National University's Research School of Earth Sciences (RSES) began a program in the Lambert Glacier region to use global positioning system (GPS) measurements to monitor any changes in the elevation of the Earth's crust, or isostatic adjustments, resulting from a changing glacial mass. This has involved installing and operating equipment in places hundreds of kilometres from the nearest permanently-staffed Antarctic stations. The solar-powered installations have transmitted recorded data automatically via satellite phone since December 2000.
The project aims to estimate absolute vertical and horizontal movements of the sites and, coupled with other geophysical data, to discriminate between several different ice models for the Antarctic continent. Three permanent GPS sites have been established on the coast at Landing Bluff, at Beaver Lake behind Amery Ice Shelf, and Dalton Corner 450 km inland. A fourth installation is planned at Komsomolskiy Peak in the 2002–03 season.
Solar-powered equipment at Landing Bluff and Beaver Lake consists of an Ashtech Z-12 GPS receiver, a PC-104 computer, a Satcom-B satellite phone and an in-house designed and built power controlling system (PCON). Careful integration of power dissipation and insulation has resulted in a system that sustains itself while solar power is available. Internal operating temperatures are typically between 10 and 30 degrees.
When solar power is inadequate for operating the GPS receiver, the PCON reverts the system to a 'hibernation' mode in which the power supply to the receiver is cut and the computer is prevented from making phone calls. Diagnostic data is still recorded by the PCON and transferred to the computer during winter while the system is hibernating. When solar power is again available in the spring the PCON wakes the system from hibernation and the GPS receiver starts recording again.
The PCON (consuming 0.7 W) runs continuously. Every 20 minutes it logs data on the battery voltages, internal and external temperatures and atmospheric pressure, providing valuable feedback to scientists on the performance of the system. If sufficient power is available, it provides power to the GPS receiver (12.5 W) which records satellite GPS data every 30 seconds.
Every 24 hours the PCON powers up the computer which downloads the data from the GPS receiver and the system diagnostic data from the PCON, stores it locally on a 'flashdisk' and then, if sufficient power is available, turns on the satellite phone and transmits the data back to Canberra. It takes about 5 minutes to transmit the 300Kb of GPS data and 8Kb diagnostic data.
Data transmission worked successfully at Landing Bluff from December 2000 until May 2001 when the system hibernated. A minor design glitch (now rectified) prevented the system from restarting in the spring of 2001 but it was quickly put to work in December 2001 when our field party visited the site. A failure of the satellite phone at the Beaver Lake installation caused communication problems through 2000 and 2001, but in January 2002 one of our group, Richard Stanaway (a geodesist from RSES), was able to fix the problem.
Both sites have been regularly transmitting the GPS and diagnostic data. The communications system is designed so that scientists in Canberra can gain control of the remote computer in Antarctica and perform certain tasks including installing new software, replacing GPS receiver firmware and changing system control parameters. On learning of the behaviour of the systems in 2001 we modified our controlling program and successfully uploaded new software to both sites.
Satellite phone communications have been sporadic during 2002. Several times both sites failed to make successful connection, which we believe is due to atmospheric disturbances – we have noticed correlations between failed communications and rapid changes in temperature and pressure indicating blizzard conditions. However, with a simple command we can retrieve the missed data during the next successful data transmission.
Remote instruments such as automated meteorological stations have been operating unattended in Antarctica for many years, but the power requirements of the GPS instruments are several orders of magnitude greater, precluding use of solar-powered systems over winter. The success of our remote systems represents a considerable breakthrough in the operation of relatively high-powered remote equipment. Furthermore, we have been able to retrieve and provide GPS data from our two sites to support the research of other scientists working in the area, thereby permitting their analysis to be performed in 2002 rather than having to wait until the next summer season for our data to be retrieved. The GPS data are of high quality and we expect that, after the next summer season, we will have accurate velocity estimates at our GPS sites, enabling the scientific goals of the experiment to be met.
Further information about the project can be found at Antarctic GPS Project.
Acknowledgements: The electronics group at the Research School of Earth Sciences for developing the electronics for these installations; also station leaders, field personnel, voyage leaders, helicopter pilots and AAD staff for logistic support.
Paul Tregoning, Richard Stanaway and Herb McQueen, Research School of Earth Sciences, The Australian National University