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 re-occupied in 1992 and 1998.
The HPGN network was displaced by the Mw = 7.1 earthquake near Hector Mine on October 16, 2000.
As a result, a large number of stations were re-visited during a 12 day campaign in May 2000.
The experiment was conducted using dual-frequency geodetic receivers and consisted of 61 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), the Bay Area Regional Deformation Network
(BARD), the Continuously Operated Reference Stations
(CORS), and the Jet Propulsion Laboratory
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 SIO final orbits as
submitted to 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 of IGS stations, for each of the 12 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
together with the global SIO solution to obtain an estimate of station coordinates, averaged over
the multi-day experiment. The regional reference frame is that of the National Spatial Reference
System and defined by the following stations: CARR, WINT, MHCB, MONP, AOA1, CAT1, VNDP, D368 and D364.
The parameters for these stations (coordinates & velocities) were provided by NGS and transformed
from NAD83 to ITRF97 using the published transformation parameters. The reference frame was then
imposed by performing an six parameter
transformation on the loosely constrained CSRC solution to best fit the NSRS.
The above products were generated by CSRC and sanctioned by NGS in March 2001.
of all sites processed. Includes sites that were not sanctioned by the NGS due to a short period
of record, marker reference point issues, or an undetermined height change during operation.
Therefore, the sites on this map will differ from the
map of all NGS-sanctioned sites. These maps are currently unavailable.
The final GLOBK adjustment included a total of 241 stations, of which 61 were part of the
Hector Mine Survey (HPGN). The additional stations are all the California CORS that were
active and healthy during the time of the survey. They include 91 stations that were not in
CSRC's HPGN 1998 analysis and 140 stations that do not have NGS sanctioned coordinates yet.
The daily coordinate repeatability of the 61 HPGN stations was 2.9/3.1/8.5 millimeters
in North, East and Vertical direction, respectively.