Contents:

• Objectives
• Publications
• Small-Scale Deformation Associated with the Landers Earthquake Mapped by SAR Interferometry, JGR, v. 103, p. 27001-27016, 1998.
• Phase Gradient Approach to Stacking Interferograms, JGR, v. 103, p. 30183-30204, 1998.
• Near-Real-Time Radar Interferometry of the Mw 7.1 Hector Mine Earthquake - in press, GRL,May 2000.
• Topographic Recovery from Stacked ERS interferometry - in press, JGR, May 2000.
• X-Band Downlink
• Near-Real-Time Data Acquisition and Processing

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

• Fresh orbital elements for relevant satellites are gathered each day at 17:00 GMT  from the Naval Space Command under an MOU with SIO.
• TeraScan software directs the 5-m dish to track every ERS-2 overflight.
• X-band telemetry is monitored, digitized, and written to a local raid-disk array whenever the radar is turned on.
• When the pass is complete, the raw telemetry is frame synchronized, converted to ESA/DPAF format, and copied to a 64 Gbyte raid disk for intermediate storage.
• Relevant files are written to the IGPP mass storage area and deleted after two days.
• (Note there is still a problem with antenna pointing accuracy; sometimes data are lost when the satellite is overhead.  We are currently working with Scientific Atlanta engineers to solve this problem.)

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.

• Accurate Time ? Each raw ERS-2 SAR echo is time-tagged using the onboard clock.  These relative times are converted to absolute time (~1 millisecond accuracy) using PATN files provided by ESA on a daily basis.
• Accurate Orbits ? Three types of accurate orbits, all provided by Delft University [Scharroo et al., 1998] are used (http://deos.lr.tudelft.nl/ers/precorbs/status.html).  Precise orbits (~0.05 m accuracy) with about a 6 month delay are available for the entire ERS-1 and ERS-2 missions.  Fast delivery orbits (< 0.10-m accuracy) with about a 5-day delay are used for near-real time analysis.  Real-time orbital predictions are available for real-time interferometry.  All three types of orbits are generated to support the NOAA real-time radar altimetry program for ERS-2.