[1] We present results from a radar interferometry study over the Houston-Galveston, Texas Gulf Coast region. From the nearly 60 potential interferograms considered, an atmospheric artifact assessment is performed and a tractable set of interferograms selected for detailed processing and error analysis. The subsequent interferogram time series spanning 1996-1998 is constrained by coincident extensometer data with root-meansquare error less than 2.5 mm. The interferogram time series confirms that historic subsidence in east Houston has stopped. Consistent with current groundwater use patterns, broad-scale subsidence bowls are observed in west and northwest Houston, where maximum subsidence rates are in excess of 2 and 4 cm yr À1 , respectively. Linear interferogram phase signatures associated with approximately 1 cm of differential subsidence across faults, including the Long Point fault in northwest Houston, are observed. Near the Seabrook extensometer, a hereto-unidentified subsidence bowl with a maximum subsidence rate in excess of 3 cm yr À1 is revealed. This study demonstrates that when used in conjunction with a set of traditional geodetic measurements, radar interferometry can measure the spatial and temporal evolution of urban land subsidence within even the most challenging of environments.
ABSTRACT:NASADEM is a near-global elevation model that is being produced primarily by completely reprocessing the Shuttle Radar Topography Mission (SRTM) radar data and then merging it with refined ASTER GDEM elevations. The new and improved SRTM elevations in NASADEM result from better vertical control of each SRTM data swath via reference to ICESat elevations and from SRTM void reductions using advanced interferometric unwrapping algorithms. Remnant voids will be filled primarily by GDEM3, but with reduction of GDEM glitches (mostly related to clouds) and therefore with only minor need for secondary sources of fill.
ABSTRACT:NASADEM is a near-global elevation model that is being produced primarily by completely reprocessing the Shuttle Radar Topography Mission (SRTM) radar data and then merging it with refined ASTER GDEM elevations. The new and improved SRTM elevations in NASADEM result from better vertical control of each SRTM data swath via reference to ICESat elevations and from SRTM void reductions using advanced interferometric unwrapping algorithms. Remnant voids will be filled primarily by GDEM3, but with reduction of GDEM glitches (mostly related to clouds) and therefore with only minor need for secondary sources of fill.
Geophysical and remote-sensing methods were applied to better understand sinkhole precursor movement and assess the potential for sinkhole development in evaporitic areas. The approach is illustrated with two examples over bedded salt deposits and a salt dome in Texas, USA. Large sinkholes (90 to 200 m in diameter) formed over Permian bedded salt near Wink in western Texas in June 1980 and May 2002, and on the flank of a coastal-plain salt dome in Daisetta in May 2008. Residents, government officials, and industry representatives wish to better understand the potential for sinkhole formation and growth in both areas. At Wink, limited spatial and temporal data on vertical ground movement from standard surveying has been greatly extended by satellite-based radar interferometry, which was used to delineate areas having recent movement and determine rates of movement. Results from interferometry guided site-specific investigations that included acquisition of high-resolution gravity data, which identified shallow-source mass deficits that indicate potential for continued subsidence or sinkhole formation. At Daisetta, interferometry was used to determine that no detectable subsidence preceded sinkhole collapse (indicating sudden collapse once the upward-migrating void reached a depth that allowed the cohesiveness of overlying semiconsolidated sediments to be overcome), and gravimetry was used to identify other areas where shallow mass deficits exist across the salt dome. Data from both areas can be used to construct risk maps, design comprehensive subsurface investigations, and develop monitoring programs based on repeat radar interferometry and geodetic GPS measurements.
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