InSAR/GPS Integration

We are integrating Interferometric Synthetic Aperture Radar (InSAR), continuous Global Positioning System (CGPS) geodesy and ground-based GPS meteorology (GPS Met) into a single geodetic instrument that will measure crustal deformation to 1 mm/yr precision with unprecedented spatial coverage. If successful, this instrument will be able to determine motion at millions of points, rather than the few hundred being measured with current geodetic methods. Our goal is to develop a technique to measure interseismic, coseismic, and postseismic deformation, and, by relating these to seismicity and geological structures, probe plate boundary kinematics (e.g., microplate tectonics versus continuum tectonics; thick-skinned versus thin-skinned models). Also, measuring the complete deformation field would be very valuable in assessing earthquake hazard. Through our involvement in the Southern California Earthquake Center we would be able to apply our results immediately.

The southwestern U.S. has already demonstrated to be an ideal location for using INSAR methods to measure ground displacements. These applications have so far been confined to coseismic and postseismic motions. We propose to use SAR imagery collected by ERS-1/2, JERS-1 and RADARSAT to measure interseismic motions with respect to the southern California array of permanent GPS receivers. Our approach will use the CGPS data to reduce two of the current error sources in determining ground displacements with INSAR:

• the "baseline" or orbital errors. We will place radar reflectors/transponders at some of the GPS sites. The SAR data covering each of these points will thus correspond to a precisely-located point, and so could be used to provide 3-D control on the spacecraft orbit and improve the accuracy of the ground displacement measurement.

• troposphere propagation errors. We will use suitably equipped continuous GPS stations, meteorological satellites, and regional-scale mesoscale models to map the spatial and temporal distribution of water vapor over southern California. Temporal variations in the horizontal gradients of line-of-sight integrated water vapor, if not properly accounted for, can produce artifacts in the radar displacement fields with magnitudes ~ 1 cm; our maps will allow us to correct for these errors.

In the first year, we will acquire at least six repeat passes of a pair of ERS-1/2 radar images covering the Los Angeles Basin and surroundings, taking advantage of the dense concentration of CGPS sites. Deformation within the basin is dominated by contraction at a rate of approximately 7 mm/yr and consequently thrust faulting. We will construct 10 radar reflectors,deploy them within the basin, and tie them precisely to the CGPS sites by GPS survey. We will evaluate the efficacy of radar reflectors and investigate the option of installing radio transponders. In the second year, will deploy another 10 radar reflectors or radio transponders.

In the second and third years, we will acquire radar images through the Scripps X-band down-link, also investigating the southern San Andreas fault, the San Jacinto fault, and the Salton trough where the number of continuous GPS stations is lower but the deformation rate is higher and primarily dextral.

We are developing software to convert raw radar echoes into single look complex (SLC) images and then into geolocated and corrected interferograms. However, to routinely monitor crustal deformation over large areas and utilize the ancillary information provided by the CGPS array, radar reflectors/transponders, and meteorological sensors will require a great deal of integration and automation. To achieve our objectives, we have assembled investigators from several institutions, who between them combine backgrounds in satellite geodesy/GPS, interferometric SAR, GPS meteorology, satellite radar altimetry, earthquake seismology, neotectonics and satellite data acquisition systems.