LITERATURE CITED
reducing weak internal and external noise (or clutter)
that occurs at constant time delay, was only partially
Arcone, S.A. (1995) Numerical studies of the radia-
successful. We have ascribed this result to the effects
tion patterns of resistively loaded dipoles. Journal of
of uneven towing speeds and erratic contact between
Applied Geophysics, 33: 3952.
the ground surface and antenna faces upon antenna leak-
age. We recommend that a simple antenna platform,
Arcone, S.A., D.E. Lawson, A.J. Delaney, J.C.
Strasser, and J.D. Strasser (in prep) Ground-penetrat-
consisting of a heavy, high-density polyethylene "boat,"
be used to contain the antenna. The prow of the boat
ing radar reflection profiling of groundwater and bed-
would help to deflect vegetation, and the weight would
rock in an area of discontinuous permafrost. Geophys-
improve ground contact. The dielectric permittivity of
ics.
the material is intermediate between air and ground and
Bowman, J.J., T.B.A. Senior, and P.L.E. Uslenghi
may improve the antenna impedance match with the near
surface. The use of this platform may make the ampli-
by Simple Shapes. New York: Elsevier.
tude of the clutter bands more uniform and subject to better
Brillouin, L. (1960) Wave Propagation and Group Ve-
removal with horizontal filters.
locity. New York: Academic Press.
We recommend that improved jitter control be speci-
Clarke, T.S., and C.R. Bentley (1994) High-resolu-
fied in the design of future transmitters and receivers.
tion radar on Ice Stream B2, Antarctica: Measurements
Jitter is the slight shift in time that occurs in signal po-
of electromagnetic wave speed in firn and strain his-
sition from trace to trace. Although jitter may be only
tory from buried crevasses. Annals of Glaciology, 20:
12 ns, its reduction could significantly reduce noise
153159.
when the trace length is only 3050 ns.
Debye, P. (1929) Polar Molecules. Mineola, New York:
We recommend that antennas for UXO detection re-
Dover Publications.
main on the surface. Airborne profiling, even at mini-
Delaney, A.J., and S.A. Arcone (1984) Dielectric mea-
mal heights of a few tens of centimeters, introduces an
surements of frozen silt using time domain reflectom-
extra dielectric layer (air) into the propagation medium.
etry. Cold Regions Science and Technology, 9: 3946.
In airborne profiling, returns from uneven subsurface
Feynman, R.P., R.B. Leighton, and M. Sands (1964)
interfaces will be strongly refracted along the surface
The Feynman Lectures on Physics, Vol. II. Reading,
and not be received because the value of ε′ = 1 for air
Massachusetts: Addison Wesley Longman.
contrasts sharply with the ε′ of the soil.
Geng, N., C.E. Baum, and L. Carin (1999) On the
The wavelet shape transmitted by present, commer-
low-frequency natural response of conductivity and
cially available systems is probably most practical. Our
permeable targets. IEEE Transactions on Geoscience
theoretical studies show that shorter pulse length, which
and Remote Sensing, 37(1): 347359.
may be available with unshielded antennas, may shift
Hoekstra, P., and A.J. Delaney (1974) Dielectric prop-
erties of soils at UHF and microwave frequencies. Jour-
too much in local frequency to be detected after propa-
nal of Geophysical Research, 79: 16991708.
gation.
Hoekstra, P., and W.T. Doyle (1971) Dielectric relax-
Future surveys should address the problem of total
ation of surface adsorbed water. Journal of Colloid and
soil saturation. Our surveys were conducted in early
Interface Science, 36: 513521.
fall, by which time these soils are usually below satu-
Jezek, K.C., C.R. Bentley, and J.W. Clough (1979)
ration. However, saturation levels are usually reached
Electromagnetic sounding of bottom crevasses on the
by late winter and can persist into late spring. Satu-
rated soils have higher values of εs* and frel and may
Ross Ice Shelf, Antarctica. Journal of Glaciology, 24:
therefore offer less attenuation per meter at 300600
321330.
MHz than would moist soils. However, mechanical op-
Kong, J.A. (1990) Electromagnetic Wave Theory. New
eration in mud may be a serious mobility problem.
York: John Wiley and Sons.
EMI systems have shown themselves to be quite suc-
cessful at UXO detection, even in site conditions that
JPG. Engineer Research and Development Center,
are unfavorable for GPR. At the same time, simula-
Vicksburg, Mississippi, Technical Report.
tions show the distinct possibility that GPR may reveal
NAVEOD (1997) Unexploded ordnance (UXO): An
key target characteristics, such as length and diameter.
overview. Naval Explosive Ordnance Disposal Tech-
This suggests that more such simulation should be done
nology Division, UXO Countermeasures Department,
and integrated into signal interpretation, and that the
Indian Head, Maryland.
most important offering of GPR may be in the realm of
Nickell, A.K. (1985) Soil Survey of Jefferson County,
discrimination more than UXO detection. Fully polari-
Indiana. U.S. Department of Agriculture, Soil Conser-
metric GPR is both possible and potentially advantageous.
vation Service, 169 pp.
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