fallout in the downwind direction was obtained. Contours were established in the upwind and crosswind directions by collections on raft stations located in the lagoon. Elaborate plans to measure the fallout in all directions around the shot point were made for Operation Castle (Reference 5). These plans involved the use of collectors mounted on freefloating buoys placed in four concentric circles around the shot point shortly before detonation. Raft stations were also used in the lagoon and land stations were located on a numberof the islands. Because of poor predictability of detonation times and operational difficulties caused by high seas, only fragmentary data was obtained from these stations. The measurement of activity levels on several neighboring atolls that were unexpectedly contaminated by debris from Shot 1 of Operation Castle provided the most useful data concerning the magnitude of the fallout areas from multimegaton weapons (Reference 6). Later in the op‘eration, aerial and oceanographic surveys of the ocean areas were conducted and water samples were collected (References 7 and 8), These measurements, made with crude equipment constructed in the forward area, were used to calculate approximate fallout contours. The aerialsurvey data and the activity levels of the water samples served to check the contours derived from the oceanographic survey for Shot 5. No oceanographic survey was made on Shot 6; however, the contours for this shot were constructed from aerial-survey and water-sample data. In spite of the uncertainty of the contours calculated for these shots, the possibility of deter- mining the relative concentration of radioactivity in the ocean following a water-surface detonation was demonstrated. During Operation Wigwam (Reference 9), the aerial and oceanographic survey methods were again successfully tested. During Operation Castle, the question arose of just how efficiently the fallout was sampled by the instruments used on that and previous operations. Studies were made at Operation Teapot (Reference 10) to estimate this efficiency for various types of collectors located at different heights above the ground. The results demonstrated the difficulties of obtaining reliable samples and defined certain factors affecting collector efficiency. These factors were then applied in the design of the collectors and stations for Operation Redwing. 1.3 THEORY 1.3.1 General Requirements. Estimates of the area contaminated by Shot 1 during Operation Castle indicated that several thousand square miles had received significant levels of fallout (References 5, 11 and 12), but these estimates were based on very-meager data. It was considered essential, therefore, to achieve adequate documentation during Operation Redwing. Participation in a joint program designed to obtain the necessary data (Reference 13) was one of the responsibilities of this project. The program included aerial and oceanographic surveys, as well as lagoon and island surveys, whose mission was to make surface-radiation readings over large areas and collect surface-water samples (References 14, 15 and 16). Such readings and samples cannot be used directly, however, to provide a description of the contaminated material or radiation-contour values. Corrections must be madefor the characteristics of the radiation and the settling and dissolving of the fallout in the ocean. It was these corrections which were of primary interest to this project. ' . - 1.3.2 Data Requirements. Regardless of whether deposition occurs on a land or water surface, much the same basic information is required for fallout characterization, contour construction, and model evaluation, specifically: (1) fallout buildup data, including time of arrival, rate of arrival, time of cessation, and particle-size variation with time; (2) fallout composition data, including the physical characteristics, chemical components, fission content, and radionuclide composition of representative particles and samples; (3) fallout radiation data, including photon emission rate and ionizing power as a function of time; and (4) total fallout data, including the numberof fissions and amount of mass deposited per unit area, as well as the total gammaionization dose delivered to somelate time. 16