Ground Penetrating Radar Sensors

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ERS, JERS, ENVISAT--not routinely taken, use DESCW swath planner on

PC running at least Windows 2000 for orbit locations. http://earth.esa.int/services/descw/

RADARSAT--not routinely acquired, contact the TEC Imagery Office

regarding acquisitions of Radarsat data.

Other commercial imaging systems, contact the TEC Imagery Office regard-

ing acquisitions.

3-15 Ground Penetrating Radar Sensors. Ground penetrating radar (GPR) uses

electromagnetic wave propagation and back scattering to image, locate, and quantita-

tively identify changes in electrical and magnetic properties in the ground. Practical plat-

forms for the GPR include on-the-ground point measurements, profiling sleds, and near-

ground helicopter surveys. It has the highest resolution in subsurface imaging of any geo-

physical method, approaching centimeters. Depth of investigation varies from meters to

several kilometers, depending upon material properties. Detection of a subsurface feature

depends upon contrast in the dielectric electrical and magnetic properties. Interpretation

of ground penetrating radar data can lead to information about depth, orientation, size,

and shape of buried objects, and soil water content.

a. GPR is a fully operational Cold Regions Research and Engineering Laboratory

(CRREL) resource. It has been used in a variety of projects: e.g., in Antarctica profiling

for crevasses, in Alaska probing for subpermafrost water table and contaminant path-

ways, at Fort Richardson probing for buried chemical and fuel drums, and for the ice

bathymetry of rivers and lakes from a helicopter.

b. CRREL has researched the use of radar for surveys of permafrost, glaciers, and

river, lake and sea ice covers since 1974. Helicopter surveys have been used to measure

ice thickness in New Hampshire and Alaska since 1986. For reports on the use of GPR

within cold region environments, a literature search from the CRREL website

(http://www.crrel.usace.army.mil/) will provide additional information. Current applica-

c. A radar pulse is modulated at frequencies from 100 to 1000 MHz, with the lower

frequency penetrating deeper than the high frequency, but the high frequency having

better resolution than the low frequency. Basic pulse repetition rates are up to 128 Hz on

a radar line profiling system on a sled or airborne platform. Radar energy is reflected

from both surface and subsurface objects, allowing depth and thickness measurements to

be made from two-way travel time differences. An airborne speed of 25 m/s at a low al-

titude of no more than 3 m allows collection of line profile data at 75 Hz in up to 4 m of

depth with a 5-cm resolution on 1-ft (30.5 cm)-grid centers. Playback rates of 1.2

km/min. are possible for post processing of the data.

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