Chapter 2
EXPERIMENTAL
2.1
DESIGN
AERIAL PHOTOGRAPHY
Aerial photographs were taken of each of the five shot areas (Lacrosse, Zuni, Seminole,
Mohawk, and Tewa), so the apparent diameter of the crater could be measured photogram-
metrically. Exposed crater contours were also determined by the same means. An RB50E aircraft equipped with a USAF acrial mapping camera, T-11, having a 6-inch focal
length, was used to n ‘e the mapping runs. The camera was gyrostabilized and the
intervalometer was set for a forward overlap of 57 to 62 percent. Calibration certificates
are on file at USAERDL for ail T-11 cameras, thus precluding the necessity for special
calibration runs. Film was developed at EPG to insure proper coverage of the target and
then sent to Fort Belvoir for analysis.
Readings of a 1:adio altimeter, FCR 718, were taken at the beginning of each mapping
run and any variations were noted. This instrument can indicate the altitude above the
surface of the ground between 200 and 60,000 feet with an accuracy of +25 feet over smooth
terrain. The flight pattern was flown as soon after the shot as possible (approximately
H + 2 to H + 32 hours).
Photogrammetric measurements were made at USAERDL. The accuracyof the stereoplotting equipment is limited by the deviation of the altimeter reading from the true value,
since the error of the equipment is negligible by comparison.
2.2
DEPTH SOUNDINGS
Lead-line soundings were taken to determine the depth of the apparent crater below
the water surface. The time at which these soundings were taken was dependent upon the
time required for the site radiation level to decay to a value such that the total exposure
of the survey group would not amount to an important fraction of the total allowable dose
for the entire operation, viz., 3,900 mr.
2.2.1 Lacrosse.
For early preliminary results, a sounding was taken from heli-
copter positioned over apparent ground zero approximately 25 feet above the water sur~
face. The sounding was later checked against those taken from a boat and found to be in
agreement within 1 foot. When residual radiation was low enough, a survey crew of
H.'mes and Narver entered and re-established a diameter that had been used in the preshot survey and, using a skiff, made detailed soundings. Because of the symmetry indicated by postshot photography, it was determined that detailed soundings along one
diameter would be sufficient.
2.2.2 Zuni. Because of the extensive breaching of the crater, the radiation level was
low enough to make re-entry possible at an earlier time than other shots. On D+ 6, a
survey crew of Holmes and Narver went into the area and made soundings along the pre-
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