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