Figure 21. Plan view of the primary tunnel survey. Dots represent radar targets and circled dots are the more intense
echoes that are probably from metal targets. Faint reflections may also be metallic targets but with a very small radar cross
section. Bars (west of the runway) represent a dense continuum of targets. Numbers beside the dots and bars are depths to
the targets in meters. Average line spacing is 2.8 m (not drawn to scale for clarity).
ably will be constructed in this area. The straight
route is approximately 800 m long and crosses the
skiway and the taxiway. Four lines were run at an
Radar responses were recorded from numer-
average spacing of 2.8 m. The 0-m mark is within
ous subsurface features of interest at the South
a few meters of the ASTRO building.
The results of this survey are shown in Figure
and lateral extent helped calibrate findings. The
22, where dots mark the approximate location of
new water well gave a strong response and its
calculated depth was very close to its measured
clear. The accuracy of line and anomaly place-
depth. The old clean air facility was located. To
ment is probably no better than 5 m because the
mark the spot, a 4-m bamboo pole was placed at
lines had no intermediate survey marks.
point Y in Figure 5. Near its top, a plywood dia-