GPS Monitoring Networks 


Data Format


Survey GPS

The USGS occupied 31 stations in the Long Valley area each summer from 1992 to 1994, and again in 1996, 1998 and 1999. The stations were occupied for a period of 5 days during July or August. The USGS recorded dual-frequency carrier-phase and C/A-code pseudorange data at 30s intervals for at least six hours at each site. Up to seven receivers were deployed each day. At least one local station, usually CASA, was observed every day to provide a tie between stations occupied on different days. Relative station position were computed using the GIPSY software. Integer-ambiguity, ionosphere-free, improved-orbit solution solution were computed in the ITRF global reference frame by including simultaneous data from several tracking stations within North America (Marshall et al., 1997).

Continuous GPS

Continuous GPS measurements at Long Valley caldera have been made since early 1993 (for more information go to http://quake.wr.usgs.gov/research/deformation/twocolor/lv_continuous_gps.html) . Seventeen GPS receivers are now operating within and near the Long Valley. The data are processed using the GIPSY software with point positioning. Prior to plotting, "bad" measurements of position, those that deviate significantly relative to position measurements made within a 3 month window, are identified and removed. Measurement precisions (1 St Dev) for "absolute" position coordinates, i.e. relative to a global reference frame, are 3-4 mm (north), 5-6 mm (east), and 10-12 mm (vertical) using 24 hour solutions. Corresponding velocities uncertainties for a 12 months period are about 2 mm/yr in the horizontal components and 3-4 mm/yr in the vertical component (see Dixon et al., 1997).

Rapid static GPS

In September 1997, the Cascade Volcano Observatory occupied most of the existing geodetic benchmark exisisting in Long Valley caldera with rapid static GPS.

GPS on leveling benchmarks

A crew of Stanford University surveyed 44 existing leveling monuments in Long Valley caldera in July 1999, using dual frequency GPS receivers. GPS and leveling were tied to a common reference frame in the Long Valley area and the vertical deformation computed  by differencing GPS-based and leveled orthometric heights (Battaglia et al., 2003).


M. Battaglia, P. Segall, J. Murray, P. Cervelli, J. Langbein, 2003. The mechanics of unrest at Long Valley caldera, California: 1. Modeling the geometry of the source using GPS, leveling and 2-color EDM data. J Volcanol. Geotherm. Res. (in press).

Dixon, T.H., Mao, A., Bursik, M.I., Heflin, M.B., Langbein, J., Stein, R.S., and Webb, F.H., 1997, Continuous monitoring of surface deformation at Long Valley Caldera, California, with GPS: Journal of Geophysical Research, v. 102, no. B6, p. 12,017-12,034.

Marshall, G.A., Langbein, J., Stein, R.S., Lisowski, M., and Svarc, J., 1997, Inflation of Long Valley caldera, California, Basin and Range strain, and possible Mono Craters' dike opening from 1990 to 1994 GPS surveys: Geophysical Research Letters, v. 24, no. 9, p. 1003-1006.


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