DATA REQUIREMENTS Data requirements consisted of (1) preshot and postshot aerial photographs provided by Program 9; (2) topographic surveys, provided by Holmes and Narver; (3) fathometer soundings of underwater craters, provided by Holmes and Narver; and (4) miscellaneous information, such as device-shielding configuration and drilling logs. Figure 4 is a sketch of Eniwetok Atoll showing shot locations. Aerial Photography. Preshot and postshot aerial photographs were taken of Shots Cactus, Koa, Fig, and Nutmeg. An RB-50E aircraft, equipped with a gyrostabilized T-11 camera with 6-inch focal length, was used to make the mapping runs. The intervalometer was set for a forward overlap of 57 to 62 percent. Calibration certificates are on file at Engineer Research and Development Laboratories (USAERDL) for all T-11 cameras, precluding the necessity of special calibration runs. A predetermined altitude was maintained by a radio altimeter, FCR 718. This instrument can indicate altitudes between 200 and 60,000 feet with an accuracy of + 25 feet over smooth terrain. The film was developed at EPG to insure proper coverage of the target and then sent to Fort Belvoir for photogrammetric analysis. The accuracy of the stereographic data was limited by TABLE 1 Shot CRATER RADIUS DATA Yield Crater Radius Adjusted Crater Radius Ivy Mike: 10.5 Mt 2,810 1,500 Castle 1 14.5 Mt 3,000 1,530 39.5 kt 202 215 Seminole 13.5 kt 330 152 Cactus - 17 kt 170 133 2,000 770 Castle 3° Lacrosse’ Koa Fig 110 kt 500 1.38 Mt_ 306 . the deviation of the altimeter reading from the true value, since the error of the equipment was negligible by comparison. Topographic Survey. A preshot and postshot horizontal and vertical survey of ground zero was made for Shots Cactus, Koa and Fig. These measurements were made bytransit on land and by lead-line soundings underwater. The craters of Shots Cactus and Koa were large enough so that random measurements would not have sufficiently described the crater profile. Measurements, therefore, were made along 6 radii which were approximately 60 degrees apart, extending from ground zero out to 500 feet for Shot Cactus and from ground zero to 2,500 feet for Shot Koa. Zero elevations on all surveys have been taken as the datum plane on which tide tables are based: 0.5 feet below mean low-water spring tide. The vertical and horizontal controls were of a third order triangulation and ordinary leveling. Detailed crater measurements of Shots Cactus and Koa could not be made until radiation levels were low enough to permit the safe re~entry of survey crews. A depth sounding from helicopters, therefore, was planned for the Shot Cactus crater on shot day before crater changes due to later washing could take place. A practice sounding was made ona similar crater, Shot Lacrosse, and the depth at ground zero was found to have changed only 4 feet in 2 years. The early sounding was, therefore, delayed until radiation levels had decayed to about 1 r/hr. Since the Shot Koa crater was expected to breach to open water on three sides, it was felt that an early depth sounding was also necessary. This sounding was made from a boat on D+4 since a boat can enter a breached crater earlier than a helicopter, due to lower radiation levels 15 Kage lo Deleted.