UCSD/SIO Final Report
Advanced Computing Technology Applications to
SAR Interferometry and Imaging Science


Professor David T. Sandwell, dsandwell@ucsd.edu
Professor J-Bernard Minster, jbminster@ucsd.edu


Objectives - Monitoring Strain Buildup and Earthquake Displacements in California

The long-range objectives of our research are to understand the kinematics and dynamics of active plate boundaries through precise geodetic and geophysical measurements. Because the continental lithosphere has a more complex layered rheology than the oceanic lithosphere, strain across the major plate boundaries such as subduction zones and transform faults is more diffuse on the continents than it is in the oceans. For example, the strain along the 800 km long Eltanin transform fault in the South Pacific is confined to a 30 km-wide zone along two major faults. In contrast, the strain along the 800 km long San Andreas transform system occurs over a zone at least 200 km-wide containing numerous parallel faults. Thus the continental tectonics are more complicated and the location and timing of earthquake ruptures are less predictable. Earthquake damage and loss of life is a major concern in Southern California (e.g., January 13, 1994 Northridge earthquake). While timely earthquake prediction may elude us for the foreseeable future, a better understanding of the physics of the earthquake cycle may aid in earthquake preparation and seismic hazard assessment. As has already been demonstrated by other groups, the southwestern US is an ideal location to use interferometric SAR methods to measure ground displacements.  These applications have so far been confined to coseismic and postseismic motions. We propose to use SAR interferometry to also measure interseismic motions by interpolating between the existing array of permanent GPS receivers (PGGA) coordinated by the Southern California Earthquake Center with NASA and other funding.  Being able to measure the complete deformation field in space and time would be immensely valuable in understanding earthquake hazard; because of our involvement in the Southern California Earthquake Center we would be able to apply these results directly to this problem.

Near Real Time Interferometry

Direct Readout from ERS-2:
The SIO X-band ground station has been in operation since June 1, 1999.  Funding from this proposal paid for a spectrum analyzer as well as some initial data purchases.  About 3.0 Tbytes of raw SAR data from ERS-2 have been collected and about 1.3 bytes of tectonically useful data have been archived.  The system can operate without human contact although we have hired an undergraduate student to monitor the operations.  Currently there is no external funding for operating the facility although SeaSpace Co. has a commitment to keep things running.  The operations are largely automatic:

Acquisition of raw ERS-2 data

Ancillary Data -Two types of ancillary data are required for the construction of interferograms in real time as well as for the maintenance of the SAR data archive.

Near Real-Time Interferometry -Data are stored files of typically 0.5 million echoes along a single track (~ 5 Gbyte).  To create an interferogram between a newly-acquired SAR image and a stack of archive images, the start time and stop time of the master image in the stack are used along with the timing information and the precise orbits to identify the relevant records in the newly acquired pass.  Interferometric baselines are also computed.  The relevant data are then extracted from the pass file, the image is focussed (either at SIO or JPL), and the image is aligned at the sub-pixel level to the master.  Finally interferograms are constructed between the new data and any one of the members of the stack.  With ordinary workstations, an interferogram can be ready about 3 hours after the data are downlinked but this time is substantially reduced by using the interferometric code developed under this proposal.