Continuous Global Positioning System (CGPS) Stations

Science Center Objects

Measurements of elevations, aquifer-system compaction, and water levels are used to improve our understanding of the processes responsible for land-surface elevation changes. Elevation or elevation-change measurements are fundamental to monitoring land subsidence, and have been measured by using continuous GPS (CGPS) measurements and campaign global positioning system (GPS) surveying. 

 

continuous GPS mounted on a tripod, located in a field, with a solar panel in the background

Continuous Global Positioning System (CGPS) Station P303 in Los Banos, CA. 
A CGPS station continuously measures the three-dimensional (3D) position of a point on, or more specifically, near the earth's surface. For this study, scientists are primarily interested in vertical movement (subsidence and uplift), but horizontal movement can be obtained with CGPS and can also be informative for subsidence studies.  CGPS stations are used to monitor subisdence in California's Central Valley. (Credit: Michelle Sneed, USGS. Public domain.)

A CGPS station continuously measures the three-dimensional (3D) position of a point on, or more specifically, near the earth's surface. There are more than 1,000 Continuous Global Positioning System Stations operating in Western North America, and hundreds of them in California alone; many of them are managed by the Plate Boundary Observatory/UNAVCO and by Scripps Orbit and Permanent Arrary Center (SOPAC), but other groups such as Caltrans, also operate some of them as part of their Central Valley Spatial Reference Network. They generally have been constructed to monitor motions caused by plate tectonics, but are widely used for other applications, including subsidence monitoring.

These GPS stations generally collect position information every 15 seconds which are then processed to produce a daily position. These daily positions are then concatenated to produce a daily time series, which allow us to track the 3D position of the station.