Why GPS?

Over the past decade, continuous GPS has been used to measure crustal deformation rates and tectonic plate velocities to better than 1 mm/yr. Real-time kinematic (RTK) GPS processing algorithms have been developed that allow precise positioning at high frequencies and ~10 ms latencies. In addition, improved manufacturing methods and increased market competition have led to lower costs for GPS hardware. In short, GPS has matured to the point where it is now a viable and cost-effective option for performance monitoring.

At the same time, improved capabilities in computing and communications have drastically altered our working and living environments. The integration of GPS with advanced digital communications has engendered a new monitoring model, one that provides the engineer and scientist with the ability to:

• Continuously monitor 3-D position and displacement in real- or near-real time
• Monitor relative displacement between points that are not inter-visible, over station separations ranging from meters to hundreds of kilometers
• Directly monitor displacement, minimizing secondary analyses and modeling
• Remotely monitor assets via wireless communications and the Internet

A number of benefits arise from the use of GPS versus other survey and displacement monitoring techniques:

• Data that are there when needed - GPS operates continuously, without manual intervention, providing data that are there when needed. Such data can be useful, if not critical, for damage assessment and emergency response.
• High temporal density - GPS networks provide temporally dense displacement measurements for each observing station. Kinematic monitoring has been achieved at rates up to 20 Hz (and climbing). Such high rates are particularly useful for monitoring high-dynamic structures such as bridges and towers, but even lower rates (1/sec, 1/hr) can be extremely useful for monitoring slowly deforming structures such as landslides, earthen dams and volcanic hazards.
• Independent, coherent reference frame - High-precision GPS is achieved through the technique of carrier phase differential positioning, which requires the analysis of data from two (or more) GPS stations to position one (or more) monitoring GPS stations. This baseline (or network) processing approach allows us to reference our displacements to a point (or a reference frame) that is outside (not subject to) the deformation field being monitored. Therefore, GPS provides greater confidence that the deformation being observed is the complete deformation being experienced by the object being monitored. Attachment of short-baseline instruments (such as extensometers) to a stable, independent, coherent reference may be difficult or impossible. And if the deformation is extensive, survey systems that require line-of-sight visibility may not be viable.

Applications

Orion's GPS solutions can be used to monitor a wide variety of structures and geologic features:

Station designs and data processing approaches are individually tuned to provide the best solution for each monitoring problem at the most cost-effective price.