Because Shot Umbrella was located inside Eniwetok lagoon, most FFP’s could be anchored prior to the shot, which substantially increased their value. In both shots, however, some provision for assessing dose accumulated from radioactive water after passage of the cloud had to be made. This requirement was met by dropping a second group of FFP’s as soon after cessation of fallout as radiological safety permitted; thus, the continuing water dosage was measured directly. All FFP positions were to be determined from locally measured drift rates and from two photomosaic maps flown as near zero time aS was practicable, one before and one after the shot. The only anomalous exposures of FFP’s considered possible were those due to the upwelling (Appendix F) of contaminated water; however, Wigwam data (Reference 54) indicated that only about 8 percent of the FFP record would be so vitiated. Therefore, while the FFP’s were not considered entirely essential, they were considered a valuable means of increasing the density of total dose measurements. They had the additional advantage of late placement, which would permit adjustment of the final array to surface winds existing at shot time. Three additional GITR’s and a number of film packs were installed aboard each of the three DD’s and the EC-2 in the target array (Figures 1.12 through 1.14}. These shipboard detectors were used as correlation points for a detailed radiological survey of these vessels. Predictions of the total gamma dose at specific locations aboard a DD maneuvering close to similar underwater atomic bursts could then be made by combining the gamma dose over a sequence of positions on various isodose contours and by applying the empirical conversion factor for a particular location aboard the vessel. Such predictions of gamma dose aboard a maneuvering DD were not undertaken by the project but presumably will be done in the analyses of subsequent operations. In addition to shipboard gamma detectors, a number of aerosol collections and test-panel exposures were made aboard each of the target destroyers. Two smaller platforms were in- Stalled aboard the DD-474 and DD-593 on top of the after stacks, as shown in Figure 1.12; these platforms were equipped with four open-close collectors (OCC) and a control box (Figure 1.15). Ome larger platform installed aboard DD-592 was equipped with four OCC’s, four alwaysopen collectors (AOC), two IC’s corresponding to those installed aboard the coracles, an airfiltration instrument (AFI), a wind-speed-and-direction indicator (WSDI), and an additional GITR (Figures 1.13 and 1.16). / Samples collected by the AFI, the OCC’s and the AOC’s provided information on the fraction of device deposited per unit area and on particle-size distribution required for interpretation of the gamma field. The OCC’s were also used to expose test panels, which were later analyzed to develop better simulants of fallout originating from an underwater burst. Collections made by the AFI and the two IC’s were analyzed for physical and chemical parameters of the base surge. A few additional collections were made simply by placing bottles equipped with funnels at certain locations in the array. These so-called funnel samples (FS) were used only for chemical analysis. Measurements obtained from these limited aeroso! collections are reported here only to the extent that they influence the basic gamma-field determinations made by the project. 43