ERS Data Usage and Justification for Further Data - February, 1998

David T. Sandwell
Scripps Institution of Oceanography
University of California at San Diego
La Jolla, CA 92093-0225

1) Research and teaching program

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. 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.

There are three completely new innovative aspects to this project that have not been incorporated into other InSAR processing systems or research programs:

i) We have developed a new method for stacking and differencing interferograms without first unwrapping the phase.

ii) We will use the Southern California GPS array to estimate the delay of the radar echos through the ionosphere and troposphere and to eventually correct the interferograms to an accuracy of better than 20 mm across a 100 km-wide frame.

iii) We use precise orbits provided by Delft University to automate all of the InSAR processing software.

The focus of our program is basic research and graduate-level teaching; funding is from the National Science Foundation and NASA. Our group consists of 3 professors (Yehuda Bock, Jean-Bernard Minster and David T Sandwell), 3 post doctorate researchers (Gidi Baer, Robert Mellors, and Simon Williams), 5 graduate students (Suzanne Lyons, Richard Jayne, Rosanne Nikoliadis, Evelyn Price, and Karen Watson), and 2 programmers (Paul Jamason and Nadya Williams). Most of the people in this group have other research assignments but we meet bi-weekly to discuss progress. Ph.D. theses for Evelyn Price and Karen Watson will rely on access to raw ERS SAR data.

2) Usage of previously purchased frames

Approximately 30 frames of raw SAR data, were purchased from RSI. They are being used to develop methods and to assess the overall data requirements. The results have been presented at a number of meetings. One of our more important findings is related to the accuracy and resolution of a DEM that can be constructed by stacking Tandem interferograms. Because of radar noise, layover, orbit error, and ionospheric/atmospheric delay, a high-resolution DEM cannot be recovered from a single interferometric pair, especially in rugged areas. We found that by stacking many interferograms having a suite of baselines (18-400 m), one can recover topography to an vertical accuracy of about 2 m on 16 m horizontal postings. The implication is that in un-vegetated areas, ERS Tandem data may provide a DEM of unsurpassed resolution and accuracy

Relevant publications:

Bock, Y. and S. Williams, "Integrated satellite interferometry in southern California," Eos Trans. AGU, 78,1997 (p.293,299-300).

Price, E. J. and D. T. Sandwell, Small-scale deformation associated with the Landers 1992 earthquake mapped by SAR Interferometry, submitted to J. Geophys. Res., revised January 1998.

Sandwell, D.T. and E.J. Price, Sums and Differences of Interferograms, submitted to J. Geophys. Res. January, 1998

Williams, S.D.P., Y. Bock and P. Fang, Integrated satellite interferometry: Tropospheric noise, GPS estimates and their implications, submitted to J. Geophys. Res., February, 1998.

3) Future data needs

We have identified 577 frames in the ESA archive that would be desirable for monitoring strain in Southern California and eventually we would like to purchase about one half of these. Our original NSF/NASA proposal (September 1996) included a request for $96,000 to purchase 240 frames at the $400/frame research price. NSF and NASA agreed to fund the project but eliminated all funding for data purchases with an understanding that NASA would negotiate with ESA to obtain the data. These negotiations were not successful so in December of 1997 we obtained permission to purchase data at the research rate. Currently have about $40,000 in our budget and will probably have another $40,000 next year. We have assembled a detailed list of 71 frames that we wish to order immediately.