Interferometric synthetic-aperture radar (InSAR)
Geodesists are, for the most part, a patient and hardworking lot. A day spent hiking to a distant peak, hours spent waiting for clouds to clear a line-of-sight between observation points, weeks spent moving methodically along a level line — such is the normal pulse of the geodetic profession. The fruits of such labors are all the more precious because they are so scarce. A good day spent with an electronic distance meter (EDM) or level typically produces fewer than a dozen data points. A year of tiltmeter output sampled at ten-minute intervals constitutes less than half a megabyte of data. All of the leveling data ever collected at Yellowstone Caldera fit comfortably on a single PC diskette! These quantities are trivial by modern datastorage standards, in spite of the considerable efforts expended to produce them.
KeywordsGlobal Position System Shuttle Radar Topography Mission Earthquake Swarm Advance Land Observe Satellite Advance Land Observe Satellite
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- 13.SRTM’s primary objective was to produce a worldwide DEM with I arc-second (~30 m) spatial resolution, 16 m absolute height accuracy, and 10 m relative height accuracy (Farr and Kobrick, 2000). Plans to distribute global SRTM data were sharply curtailed after II September 2001 for reasons of US national security. SRTM data with 30 m spatial resolution are currently available for the US, and with 90 m resolution for all of North America and South America. Data for other continents will follow. Portions of the 30 m dataset outside of the US are available for scientific applications by special request. SRTM DEM data can be accessed at http://seamless.usgs.gov/.
- 20.The year-to-year range changes are small enough to have been caused by tropospheric-path delays, as discussed by Beauducel etal. (2000) for Mount Etna, but three lines of evidence point instead to ground deformation as the cause: (1) the fringes around Norris Geyser Basin appear in several independent interferograms spanning similar time periods, (2) the Norris area is relatively flat so there is no reason to suspect a strong topographic influence on tropospheric water vapor concentration, and (3) the uplift inferred from InSAR was corroborated by comparison of leveling results from 1987 and 2004 (CVO, unpublished data).Google Scholar
- 23.Volcanic Explosivity Index (VEI): a measure of the size of volcanic eruptions akin to the Richter magnitude scale for earthquakes. The VEI is a 0-to-8 index of increasing explosivity, each interval representing an increase of about a factor of ten. It combines total volume of explosive products, eruptive cloud height, descriptive terms, and other measures (Newhall and Self, 1982).Google Scholar