Contents:

• Abstract
• Investigators
• Monitoring Tectonic Deformation/Earthquakes
• X-Band Downlink
• Theory/Software
• Final Report

We have assembled a balanced team of Synthetic Aperture Radar (SAR) technologists, HPCC specialists, and Earth scientists to conduct an aggressive program in scalable SAR computing technology with applications to the Earth sciences. Our perspective is that by developing a core suite of portable, scalable SAR software in image formation and image interferometry, we can enable the instantiation of SAR processing capability on a large percentage of NASA's, and indeed the entire nation's, inventory of HPCC assets. Then by further developing a network computing model for this same software suite, we can access the raw data needed, bring that data to any one or to multiple machines on that network for execution, and return the results to a desired location. We focus on both scalable data processing and scalable data movement. This positions SAR data processing advantageously in two key respects:The processing can be moved away from special purpose SAR correlators and positions its (high performance) execution within a processing on demand environment initiated and guided by the end user scientist.

Many options are created for high volume SAR projects including load balancing the computation over several institutionally managed supercomputers. SAR is proving to be invaluable for a very wide variety of Earth Science applications.[Evans, 95a] Accordingly, our Earth Science sub team proposes to accomplish three distinct projects with these new computation capabilities.

We propose in-depth scientific studies in:

• Alpine glaciers world-wide,
• Tectonic monitoring, and
• Rain forest evolution assessment

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 (Figure 2 [Massonnet:93]; see also [Zebker:94b]).

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. Over the next year we will install radar reflectors at enough of these sites to provide 3-D control on SAR images from RADARSAT and ERS-1/2. With a sufficiently accurate digital elevation model, repeating pairs of C-band SAR images can be used to generate interference fringes. A major problem in interpreting these images is caused by inaccuracies in the spacecraft position. A few radar reflectors, imaged in the same 100 km by 100 km scene, could be used to refine the positioning accuracy needed to detect small ground motions.

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. The region that we propose to monitor is about 600 km by 300 km. One satellite, such as RADARSAT, can provide complete coverage every 12 days. Single-look complex (SLC) images at full resolution are needed to create interferograms. With a pixel size of 4 by 8 m this corresponds to about 30 gigabytes of processed SLC data every 12 days or about 1 terabyte a year. The raw SAR data are somewhat larger and the processing of these data into SLC images is a formidable task as described above. In addition, we hope to acquire data from other satellites such as ERS-2, and JERS-1 which places additional demands on the S4 system.

Extension of the CASA network with other computational aspects include computing interferograms among possible coincident images, unwrapping the phase maps of the deformation, and adjusting the interferograms to match the GPS observations. Such a large scale of production will require routine processing and archive at a supercomputer facility; the high speed link to Scripps shown in Figure 1 will be used to interactively view and validate the intermediate results. Our specific objectives are:

• To generate a highly accurate, uniformly sampled digital elevation model for the region. Such a product is fundamental to many areas of research (e.g. hydrogeology) but in this case it also simplifies interferometric SAR processing so that two images suffice to detect ground displacement.
• To understand short-term transients associated with the delay of the radar echo through the troposphere and ionosphere and mitigate the contamination of the interferograms by these effects.
• To use the repeat images to attempt to unravel the co-seismic, post-seismic and interseismic components of crustal deformation within the plate boundary zone. For this purpose, simultaneous analysis of data collected by the dense GPS network and SAR images would permit us to take advantage of the continuous temporal coverage of the former and the continuous spatial coverage of the latter.

[Canizares 95] Letter from the National Research Council to NASA describing their preliminary findings on the importance of SAR, Canizares, C.R., McElroy, J.H.,April, 1995

[Chapman:94] "Validation and calibration of J-ERS-1 SAR imagery", B. Chapman, M. Alves, and A. Freeman, J-ERS Results Reporting Meeting, December 1994, Tokyo, Japan

[Curkendall:94] Early Results in SAR and Visualization on the Cray T Presentation at CUG, Oct. 94, Tours, France.

[Evans:95] Spaceborne Synthetic Aperture Radar: Current Status and Future Directions, Space Studies Board, National Research Council, NASA, Evans, D.L., Editor, April, 1995

[Feigl:93] Space Geodetic measurements of crustal deformation in Central and Southern California, Feigl, K., D. C. Agnew, Y. Bock, D. Dong, A. Donnellan, B. Hager, T. Herring, D. D. Jackson, T. H. Jordan, R. W. King, S. Larsen, K. M. Larson, M. H. Murray, Z. Shen, and F. Webb, 1984-1992, J. Geophys. Res., 98, 21677-21712, 1993.

[Freeman:94]"Amazon rain forest classification using JERS-1 SAR data", A. Freeman, C. Kramer, M. Alves, and B. Chapman, JERS Results Reporting Meeting, December 1994, Tokyo, Japan

[Gabriel:89] Mapping small elevation changes over large areas: differential radar interferometry; Gabriel, A.K., Goldstein, R.M., and Zebker, H.A.; Journal of Geophysical Research, Vol. 94, no. B7, pp. 9183-9191

[Hess:95] "Delineation of inundated area and vegetation along the Amazon floodplain with the SIR-C synthetic aperture radar",Hess, l.L., J.M. Melack, S. Filoso and Y. Wang, IEEE Trans. Geosc. Remote Sens., 1995.

[JERS-1:94] JERS-1 Data Users Handbook, Earth Observation Center, National Space Development Agency of Japan, Dec. 1994 [Massonnet:95] The displacement field of the Landers earthquake mapped by radar interferometry, Massonnet, D., M. Rossi, C. Carmona, F. Adragna, G. Pelzer, K. Feigl, and T. Rabaute, Nature, 364, 138-142, 1993.

[Mertes:95] "Spatial patterns of hydrology, geomorphology and vegetation on the floodplain of the Amazon river in Brazil", Mertes, A.K.L., D.L. Daniel, J.M. Melack, B. Nelson, L.A. Martinelli and B. Forsberg, J. Geomorphology, 1995.

[RADAMBRASIL:83] Projecto RADAMBRASIL, Ministerio das Minas e Energia, Departamento Nacional de Producao Mineral, Levantamento de Redurso Natukrais, Vols. 1-23, Rio de Janeiro, 1973-1983.

[Rott:92] Multifrequency and polarimetric SAR observations on alpine glaciers, H. Rott and R. E. Davis, Annals of Glaciology, 17: 304-308, 1992.

[Shi:94] Snow mapping in alpine regions with synthetic aperture radar, J. Shi, J. Dozier, and H. Rott, IEEE Transactions on Geoscience and Remote Sensing, 32(1): 152?158, 1994.

[Siegel:94] "Parallel Processing of Spaceborne Imaging Radar Data," Payne, D., Phung, T., Miller, C., Siegel, H., Williams, R., Consurrent Supercomputing Consortium Annual Report 1993-1994

[Stein:89] Hidden earthquakes, Stein, R. S., and R. S. Yeats, Sci. Am., 260, 48-57, 1989.

[Wang:95] "Detection of flooding in Amazonian forests : results from canopy backscatter modeling", Wang, Y., S. Filoso, L. Hess, and J.M.Melack, Remote Sensing of the Environment, 1995

[Zebker:86a] Topographic Mapping from Interferometric SAR Observations; Zebker, H. and Goldstein, 1986l Journal of Geophysical Research, Vol. 91, B5, pp. 4993-4999

[Zebker:94b] On the derivation of coseismic displacement fields using differential radar interferometry: The Landers earthquake, Zebker, H. A., P. A. Rosen, and R. M. Goldstein, J. Geophys. Res., 99, 19617-19634, 1994