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Bohling, Geoffrey C. / A ground penetrating radar study of water table elevation in a portion of Wisconsin's central sand plain
[DNR-050] (1988)

III. Radar theory and hydrogeological applications,   pp. 19-32 PDF (3.7 MB)


Page 22

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permittivity of the material (Horton et al., 1981; Ulriksen, 1982). Experi-
mental data indicate that e .. for a typical clay loam soil is approximately
constant for frequencies from  10 MHz to 3000 MHz (King and Smith,
1981). In this study it is assumed that the same is true for the sandy loam
soils and sands in the field area, at least over the frequencies in the 3 dB
bandwidth of the antenna employed (approximately 40 to 120 MHz).
The radar signal radiates outward and downward into the ground
from the antenna. When this signal impinges on a planar interface, such
as the water table, most of the incident energy is either transmitted into
the layer below the interface or reflected at angles that do not return to
the antenna. However, a portion of the energy which strikes the interface
at near-normal incidence will be reflected and return to the antenna. The
two-way travel time of this return signal is then recorded on a graphic
recorder with a scale calibrated in nanoseconds. A profile of return time
versus distance is produced as the radar antenna is pulled along the
ground surface. This return time profile can be converted to a depth
profile according to the formula
vt(s
2 Vt(8)
where D is the depth to a reflector of interest, t is the two-way travel
time and v is the average velocity of the radar signal between the ground
surface and the reflector. Alternatively, for a profile with multiple layers,


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