the contaminated water; and (4) as soon as the ship was well into clean water, it was swung 90
degrees and proceeded into the fallout area again and madeanother station; thus, she followed
the edge of fallout in a zig-zag fashion.
This basic procedure for the destroyer escorts was subject to whatever modifications the
control center and the chief scientist aboard each ship deemed necessary.
From the time the M/V Horizon received permission to commence the survey, her procedure
was slightly different from that of the destroyer escorts and is outlined as follows:
The Horizon too, proceeded into the fallout area on recommended course and speed, but
with the purpose of meeting the YAG 39 and taking over the penetration measurements being
made in the vicinity of a marker drogue that was previously launched by the YAG.
Either prior to or just after relieving the YAG 39, the Horizon made a Station in contaminated
water and filled the decay tank.
The measurements made in the vicinity of the drogue were by: (1) periodic stations consisting
of BT measurements, radioactivity penetration measurements, and collection of surface water
samples and (2) one station, consisting of those measurements listed above, with the addition
of a Nansen bottle cast for collection of depth samples for Project 2.63, a Similar cast for Project 2.64 water samples, a special bottle cast for collection of samples for AFOAT-1 element,
and a zooplankton net tow for collection of biological samples.
The measurements and collections made in the vicinity of this drogue were particularly valuable because the drogue was “tied” (by a parachute) to the spot of water in which it was launched.
This resulted in a study of the time variations, rather than of geographical changes in the measured values.
Maintaining position on the drogue also gave an excellent measure of the current
drift of this one mass of water. Therefore, the measurements were made around the drogue
for as long a period as possible.
Upon departure from the drogue station, the M/V Horizon made measurements and collections
in areas designated by the control center.
These, in general, were areas where deep water
samples were required or where insufficient measurements had been made by the destroyer
escorts.
All three survey ships were required to return to Bikini prior to the morning of D+5. This
was for the purpose of delivering the water samples to the flyaway aircraft. For every shot except Tewa this gave sufficient time for a complete survey.
2.5 INSTRUMENTATION
The block diagram shown in Figure 2.1 of the Project 2.62 installation on the YAG’s is also
applicable to the two destroyer escorts and the M/V Horizon. The notable difference is that
while the winch was remotely controlled on the YAG’s, such was not the case on the other three
survey vessels.
2.5.1 Underwater Detector Probe. The sensing instrumentitself was the probe and is shown
schematically in Figure 2.2. The schematic shows the components clearly enough, but a few
design points should be mentioned.
The instrument was basically composed of four separate
packs that could be replaced in the tube:
1. The towing end contained the pressure-sensing element, which was a bourdon-actuated
potentiometer across which 2.68 volts were imposed from mercury cells. The output from the
gage was a minimum at zero pressure and a maximum when full pressure was applied,
Since
all ships were not required to take measurements to the same depth, full-scale deflection for
the gages on each ship corresponded to the following depths: M/V Horizon, 800 meters; YAG
33, 400 meters; YAG 40 and two destroyer escorts, 200 meters.
The pressure-sensing elements
were checked periodically for calibration. This was accomplished, on deck, by connecting the
copper tube vent to a hydraulic pump and measuring the current output at the recorder panel as
the pressure was increased.
2. The Second section contained the high-voltage pack for the Geiger tubes. This was composed of fifteen 45-volt hearing-aid batteries and was plugged into the towing end.
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