Chapter | INTRODUCTION Attempts were made during Operation Castle to study the fallout patterns from nuclear devices detonated at the surface over land and water. Most of the fallout from the nuclear devices was distributed over extended oceen ar 2s outside the atolls on which the weapons were detorated. It was desired to detormin: whet the radtation levels would have been had the radioactive material from the test devices fellen on extended land areas. Study of Shot 1 made clear that observation of fallout on subsequent shots over larger areas was necessary. On Shot 5 alternative methods were attempted. The Division of Biology and Medicine (DBM)of the Atomic Energy Commission used airborne gamma de- tectors to measure activity on rafts. Oceanographic surveys were mounted by the Scripps Institution of Oceanography (SIO) and Naval Radiological Defense Laboratory (NRDL) in- volving submerged counters and water sampling. Studies of these data showed need for modified techniques to give a faster synoptic survey for the remaining shot, Shot 6. This was done by limiting the observations to above-surface monitoring and surface-water sampling in conjunction with a synoptic aerial survey. 1.1 OBJECTIVES The ultimate objective of the work described herein was to provide data for the determination of the amount and distribution of fallout received by ocean areas surrounding the site of a surface nuclear detonation. This information is of particular interest when related to the gammafield intensities which would exist if the fallout were received by land areas. The initial objective of the work described under Project 2.7 was to evaluate the feasibility of using oceanographic surveys and sampling techniques as a meansof providing radiological information. The specific objectives were to: (1) determine the distribution in ocean water of the major fallout downwind; (2) measure depth and rate of mixing of fallout; and (3) collect otherwise-unattainable specimens, technical data, and field experience essential for the success of future operational planning and instrumentation. 1.2 BACKGROUND This study was initiated by the Headquarters, Armed Forces Special Weapons Project’s (AFSWP) suggestion that water sampling and survey techniques could be used to estimate the fallout contours. The techniques adopted, following consultation between representa- tives of AFSWP, NRDL, and SIO, consisted of water sampling and surveys using submergible radiation instruments at several depths. The method was based upon the existence well known by oceanographic measurements of a uniformly mixed surface-water layer. Such a layer presumably is created by the