King County Road Services - Puget Reference Station Network

A multi-agency effort

The Puget Reference Station Network (PRSN) is a network of permanent Global Positioning System (GPS) Continuous Operation Reference Stations (CORS) that delivers real-time centimeter GPS corrections via cellular technology.

The PRSN Network is a regional multi-agency cooperative effort that was officially launched on Aug. 4, 2004. The PRSN will provide the region with new cost-saving GPS technology, services, and spatial information.

Why do you need a network of CORS stations? My hand held GPS unit works by itself?

The accuracy of a single GPS receiver’s position (autonomous position) is 6-11 meters under good conditions, whereas the use of two dual frequency receivers can achieve centimeter accuracies in real time.

PRSN basic components

Permanently fixed GPS receivers, GPS antennae on stable seismic antenna mounts that operate continuously.

The seismic mounts as shown above were provided by Central Washington State University’s Pacific Northwest Geodetic Array (PANGA) laboratories. PANGA was able to provide fund the stable mounts from a grant from the National Science Foundation. In exchange for the mounts, King County provided a GPS receiver, antenna, and data. Each of the metal tripod legs is grouted and buried up to 35 feet deep. This provides for sub-millimeter stability that is necessary for the scientists of PANGA to monitor seismic movement and silent earthquakes.

This cooperative effort was a win-win solution for the citizens of King County. This successful collective (Puget Reference Station Network) regional effort illustrates how costs are reduced as various agencies, academia, and individuals have pooled resources, knowledge, materials, equipment, and labor to effectively.

Through various communication infrastructure, the GPS receivers stream satellite data from CORS stations to central processing center at the Seattle Public Utilities. The real time centralization and processing of dual frequency satellite data from a network of CORS stations can provide centimeter real-time Virtual Reference Station (VRS) technology positioning solutions three times farther than a single CORS station solution.

PRSN applications

The PRSN provides centimeter real-time GPS positioning service, post processing data for millimeter positioning solutions, and may include DGPS data corrections in the future. The uses of GPS are many even without incorporation of aiding technologies.

In a nutshell, GPS is used in airborne mapping operations such as aerial photography, LIDAR, remote sensing, bathymetric; boundary and cadastre surveys; topographic surveys; hydrographic surveys; emergency and accident response surveys; construction surveys, machine control and stake-less grading; tracking and navigational, asset inventory – utility location and recovery, mobile mapping–imaging; pavement inventory; precise timing; deformation studies and seismic monitoring.

GPS may not work everywhere, however supplementing GPS with inertia systems, existing surveying technologies such as reflector-less total stations, high definition surveying equipment, laser technology, and pseudolite ranging has given the surveying profession the means to provide greater diversity, quality and efficiencies in service.

PRSN benefits

The PRSN will increase Real Time Kinematic (RTK) GPS surveying efficiencies over 25 per cent in set up time alone over conventional RTK which requires the daily set up of a base receiver and radio and setup verification checks.

The PRSN has regional coverage where ever cellular phone service is available, whereas conventional RTK would require the additional base receiver and radio and set up for each survey limited to 6 miles from the base station receiver or even less due to line of sight radio issues.

The Survey Unit has three GPS receiver-data logger rovers that it can deploy on survey sites suitable for GPS reception and cellular phone service. The scenario of using the PRSN Real time positioning service on three separate projects spread apart translates into base station set up cost-savings benefit of $300 per day. It also eliminates the need for additional base radio and receiver equipment for each project. Whether the Survey Unit or a contractor is performing the work for County, the PRSN will decrease RTK GPS operational costs over 30 percent.

NGS Height modernization and SRCW

Height modernization and the Spatial Reference Center of Washington (SRCW) is a statewide effort to improve GPS derived elevations in real time and post processing applications along with other multi-functional enhancements to a network of GPS CORS sites, a statewide reference framework of horizontal and vertical control stations.

The name "height modernization" is literally what it means. Landing airplanes, navigating large tankers with minimum vertical clearance, and other tasks requiring the determination of elevations in real time or prompt next day service, in a national vertical reference framework can be made possible by correlating GPS derived heights to said NAVD88 vertical datum. Adding this functionality not only will reduce costs by employing GPS over classical levels, its also provides the ability to re-establish vital elevations swiftly and independent of local and regional subsidence that may exist.