a. 100-MHz transducer.
b. 400-MHz transducer.
Figure 9. Profile recorded along transect 1 away from the bunker excavation.
use of the mean ε = 11.3, the time range settings
for the 100- and 400-MHz transducers provided
Eight transects were run near the bunker and
an approximate depth range of 12.4 and 2.0 m,
respectively, in these materials. The in-situ signal
selected for use in this report (1, 2, 3, 5 and 9; Fig. 5).
radar records is difficult, however, owing to the
This 50-m transect was located south of the
local variability in these glacial deposits.
known limits of the buried bunker and utilidors
(Fig. 9 and 10). The 100-MHz profile shows a sub-
surface horizon, which we interpret to be an exca-
The site was surveyed during the summer of
vation surface. It varies from a depth of 4 to 6 m,
1996, when the ground surface was dry. The con-
reaching its maximum depth about 18 m from the
trol unit and data recorder were operated from the
east side of the transect line. At distances of 0 to
front passenger seat of a 4-wheel drive vehicle and
10 m and 35 to 50 m along the transect,
powered directly from the vehicle's electrical sys-
subhorizontal reflectors resembling fluvial layer-
tem. The 100-MHz transducer was placed in a
ing are present at depths between 5 and 7 m. These
wooden sled to reduce abrasion on the bottom of
the antennas and was towed approximately 10 m
horizon that appears to be the limit of an excava-
behind the vehicle (Fig. 8a). The smaller 400-MHz
tion (i.e., probably from the time of bunker con-
transducer was pulled by hand to maintain good
struction; Fig. 9a and 10a). Fill above the excava-
contact between the antenna and the ground sur-
tion surface is characterized by closely spaced
face (Fig. 8b).