In addition to the bottom survey, aerial photographs of the cra-
ter were taken promptly after the shot. In addition, to assist in
tracking the boat carrying the fathometer, serial photographs were
taken at 2 min. intervals during the time the boat was in the crater.
The fathometer showed that the crater had refilled with very
loose sand or mid to a uniform depth after the shot. In the placement
of,the barge for Shot 2, which was to be fired at the same ground zero
logation as Shot 1, the H&N group made lead line soundings prior to the
placenent of marker buoys and moors for the barge. The data on those
soundings are also included in this report as evidence of the crater
{<!.
shape,
The: post-Shot 1 survey was conducted on the sixth day after the
shot.
At ‘the time of the survey, the radiation level 10 ft above the
water surface was 25 to 75 mr/hr. Measurements by other groups demonstrated that: the levels on the land areas surrounding the crater were
much higher. : -.
After.the accomplishment of the post-Shot 1 survey and the preShot 3 and pre-Shot.4 surveys, a discussion was held of the extent of
further effort merited in light of the uncertainties as to times and
locations of the remainder of the shots. In these discussions it was
brought out that the expected result of Shot 3 would be to remove the
western end of Tare Island to a depth of 50-100 ft. Since the preshot
survey of the water surrounding it showedthat the island had quite
steep sides, it was felt-that the measurement of the crater would have
very small value for the prediction of craters in locations where the
earth approached a uniform plane rather than a mountain top. In the
same discussion it was also confidently predicted that the result of
Shot 4 would be a relatively minor..disturbance at the bottom.
As @ result of these discussions it was agreed that a curtail-
ment of effort regarding the postshot survey of these two shots was ape
propriate and the conclusion was reached that adequate data would be
obtained if three taut wire runs could be obtained approximating three
crater diameters and that these runs could pe deferred for Shot 3 until
after Shot 4. Consequently the project{group left the forward area on
1 Apri and returned to the forward ares’ on 29April, immediately after
Shot
4.
pa
The actual postshot survey of the Shot "3 crater was somewhat
modified because the yleld was mich smaller than had been predicted
and hence the crater, instead of encompassingallrof the western end
of the island, was mich nearer to being landlocke within the western
end of the island.
In acceding to the pressure of;the continuing shot
schedule for CASTLE, it was decided not to reestablish.the Raydist e-
quipment for the postshot measurements for Shots 3 and4; and as had
been predicted the landmarks available for visual location of the ship
were inadequate.
In addition, because of the tight shot-schedule then
existent, the photographic airplane was not able to rendezvous with the
boat to assist in the location during the fathometer surveys.: ; Conse-
quently the crater dimensions were determined first by the fathometer
equipment on the ship combined with taut wire equipment and ‘later by
aerial photographic mapping techniques. In actual operation it was
found extremely difficult to maneuver the LCU in the narrow confines
22