Note: ITRF97 values were calculated at CSRC and sanctioned by NGS. NAD83 values were calculated at NGS.

   CSRC Data Portal map of 1998 survey sites.

   Results from this survey are now available via the CSRC Data Portal.

Background

The High Precision Geodetic Network (HPGN) was established by the California Department of Transportation (Caltrans) and the National Geodetic Survey (NGS) as a statewide GPS control network. The network was first visited in 1991 and again in 1992 in response to the Landers earthquake. This document describes the results of the 1998 survey, which took place between June and August of 1998. The experiment was conducted using dual-frequency geodetic receivers and consisted of 146 stations. The California Spatial Reference Center (CSRC) was contracted as an independent consultant by Caltrans to analyze these data.

During the time of the experiment, a large number of continuously operated GPS stations were active in California, established by the Southern California Integrated GPS Network (SCIGN, 51 stations), the Bay Area Regional Deformation Network (BARD, 21 stations), the Continuously Operated Reference Stations (CORS, 3 stations), and the Jet Propulsion Laboratory (JPL, 3 stations).

The data were processed using the GAMIT and GLOBK packages, developed at Scripps Institution of Oceanography (SIO) and the Massachusetts Institute of Technology (MIT). The official final orbits as provided by the International GPS Service (IGS) were used, and tightly constrained to obtain the highest precision possible. The analysis was performed in a three step procedure. First, the California CORS stations were processed, together with a selected set IGS stations, for each of the 47 days of the experiment. Secondly, the HPGN data were reduced together with data of 7 spatially distributed California CORS stations, to align the solution with a regional reference frame. Finally, the GLOBK package was used to combine the two sets of solutions to obtain an estimate of station coordinates, averaged over the multi-day experiment. The regional solution was aligned to the International Terrestrial Reference Frame 1997 (ITRF97) by tightly constraining the coordinates of a selected set of ITRF stations.

The final GLOBK adjustment included a total of 204 sessions, with 5 IGS stations, 78 California CORS stations and 146 HPGN stations. The cartesian ITRF97 coordinates and one-sigma uncertainties of the CORS stations are directly derived from this adjustment.

The overall one-sigma precision of the HPGN coordinates is 2.3 +- 0.4 mm in the north, 2.4 +- 0.4 mm in the east and 9.9 +- 2.9 mm in the vertical component. The California CORS stations have an overall coordinate precision of 1.7 +- 0.1 mm, 1.8 +- 0.1 mm and 4.2 +- 0.2 mm in the north, east and vertical components, respectively.