An Interferometric SAR Study of Subsidence in Houston, Texas
Principle Investigators:
Byron D. Tapley, University of Texas, Center for Space Research
Sean Buckley, University of Texas, Center for Space Research
Paul Rosen, Jet Propulsion Laboratory
Scott Hensley, Jet Propulsion Laboratory
William Mullican, University of Texas, Bureau of Economic Geology
Proposed Work
A critical factor in developing a strategy for future coastal development and coastal hazard mitigation is the monitoring and prediction of coastal subsidence. No where are these issues more evident than in the Houston/Galveston coastal region in Texas where subsidence dates back nearly a century and continues to the present. The University of Texas Bureau of Economic Geology (BEG) has long monitored Houston subsidence and the Harris-Galveston Coastal Subsidence District (HGCSD) was established in 1975 specifically to address the issue of subsidence mitigation in the Houston area. To focus their efforts where they are needed most, the HGCSD requires short term and long term subsidence measurements of the entire Houston area. However, current subsidence measurement techniques are either too costly, too time-consuming, or not spatially-dense enough to provide the requisite information.
This project proposes using differential interferometry to provide Houston area subsidence measurements more spatially-dense than those obtained from traditional techniques. Specifically, this project will:
- demonstrate the use of differential interferometry for observing coastal subsidence,
- measure Houston subsidence rates by developing a time series of interferometrically-derived subsidence displacement fields, and
- apply the interferometrically-derived subsidence measurements to the problem of modeling and predicting Houston subsidence.
Houston Subsidence
No where are the issues of subsidence more evident than in the Houston/Galveston coastal region in Texas. This region is characterized by a compactible clay surface, shallow oil reservoirs and large underground aquifers. Oil extraction as well as groundwater extraction to support extensive urbanization has decreased fluid pressures in reservoirs and aquifers. This has resulted in the compaction of the clay surface and widespread subsidence of the Houston area [Holdahl et al., 1991; Sharp et al., 1991].
Houston subsidence dates back nearly a century [Pratt and Johnson, 1926] and continues to the present. In areas of greatest groundwater extraction, this subsidence has reached 3 m. At benchmarks west of Houston, 1987 subsidence rates ranged from 3.1 to 7.6 cm/yr [Holdahl et al., 1991]. Present subsidence rates in West Houston are on the order of 5 cm/yr [Zilkoski, personal communication, 1996].
Houston Subsidence Measured By the Differential INSAR Technique
The Houston area is undergoing subsidence rates that should be observable using the INSAR technique with the greatest subsidence rates occurring in the center of Houston. Research has shown that the interferometric phase remains well correlated in urban areas over long periods of time [Dixon (editor), 1995]. This advantageous characteristic of urban areas will increase the likelihood of witnessing subsidence in all parts of the Houston area (one simply waits long enough to see the surface displacement) as well as allowing both short term and long term subsidence rates to be determined from a time series of subsidence displacements fields.
INSAR-derived Houston subsidence measurements will be complementary to the NGS/HGCSD GPS network subsidence measurements. Specifically, the INSAR-derived Houston subsidence measurements will provide a more spatially dense set of subsidence measurements while using the GPS network measurements as tie points. Spaceborne repeat-pass differential interferometry has the potential of providing new insight into the short term and long term subsidence of Houston every time a SAR satellite passes overhead.
Last Modified: Tue Nov 2 1999
CSR/TSGC Team Web