CHAPTER II, SECTION IA entire Atoll from which the interrelation of structures and areas and their location can be specified. Due to the limited area incorporated within the survey, the slight additional refinement obtained by computing a transverse Mercator grid would not be justified. rapidly as personnel and transportation facilities were available. The location of the high tide line of an island was the first objective, followed by more detailed surveys of the interior of the islands where required. The origin of plane coordinates N103,872.0, E£128,879.0 was taken at Station Air of the US Navy Survey which has also been adopted as the origin of geographic position. quirement for site planning was to determine The basis of bearings for this grid is a true meridian through the USN Station Air determined by adopting the adjusted value of that survey for the forward azimuth of the line USN-Air to USN-Enyu 268-00-01.4 or N&8-00-01.4E. The adjusted length of the line USN-Air to HIGH TIDE LINE SURVEYS. Thefirst re- the configuration and extent of the land areas of the project islands. The procedure was to ¢stablish a third order traverse around the perimeter of an island, the elevations of the high tide lie by relation to a preliminary vertical datuut, and locate this line by stadia observations from the traverse points. The results of the survey were plotted, thereby cbtaining an outline of the island. USN-Enyu, as determined by expansiou from the new Oboe-Sugar base line, is 51473.8 feet. The USN Survey value is 4.8 feet more, or 51478.6 feet. While this difference was within the specifications for second order triangulation, it was believed to be mainly accounted for by the stronger figures of the new survey made possible by inclusion of the lagoon Station Coca. TOPOGRAPHIC MAPPING. As site plannin progressed, more detailed surveys were required to determine the relative elevations and location of terrain conditions which would influence design. This work was accomplished by piane table mapping, generaliy at scales of 1” to 50’ or 1” to 100’ and one-foot contours, or by profiles and cross sections of an area. The adjusted length and direction of the line Oboe-Nan (USN-Enyu) as determined frem its relation to the tine USN Air-USN Enyu was adopted as the initial line for computation of geodetic and plane coordinates for this survey HYDROGRAPHY. Thedesign of causeways and beaching areas for landing craft required surveys to determine the contour of the lagoon or reef bottom in these areas and location of underwater obstructions. This was generally accomplished by soundings taken from surface craft and the location of the soundings determined by intersection of angles from shore stations. Assistance was given to the Marine Department in locating channel markers and mooring buoys. TRIANGULATION ADJUSTMENT. The computed closing crror of the triangulation net, before adjustment and using the observed angles plus or minus one-third of the closing error of a triangle, was less than 1:25,000. As the closure was wel: within second order specifications, and considering the size of the network, the additional refinement obtained by a least square adjustment could not be justified. To satisy the requirements of a plane coordinate grid. the value of a siation should remain the same independent of the direction of computation through the net. This was accomplished by applying a side equation adjustment which, while approximate, satis- fied the requirement. Plane and geodetic coordinates were computed for all primary stations based on this adjustment. The geodetic coordinates of the recovered USN Survey stations were computed as a means of comparison between the surveys. Table 2-13, Figures 2-7 thru 2-12 and Tables 2-14 thru 2.23 list the plane coordinates, station locations and geographic positions. DESIGN. Surveys to obtain information requ.red for design of project features were mitiated on arrival of the beachhead party at Bikini Atoll in October 1952. Only a small survey group could be supported at that time and top priority was given to the surveys for design and construction of the camp and airstrip at site Tare. Surv ys were igitiated on the other project islands as Page 2-24 BARGE STABILITY STUDIES. The requirement to moor Scientific Station test barges in the lagoon within specified tolerances resulted in surveys to determine the yaw, roll, pitch, and horizontal motion of @ barge around a fixed point. To determine this information, observations were taken over a period of several weeks to obtain actual measurements of the various movements of the barges. In addition, the length, period, height, and e-imuth of waves were measured and a record w. kept of the direction and velocity of the wind. WAVE AND CURRENT STUDIES. Support was given to representatives of the USN Hydro- graphic Office in determining wave and current studies within the lagoon and seaward from the channels through the reef. A survey party assistect by locating the observation points py sextant angles to shore stations. CHANNEL LOCATION,Support wasalso given a USN Uydrographic Office group in determining the locations of channels within the lagoon for deep draft vessels. The wire dragging of these areas was located from controls established by this department and department personnel assisted in the opcrations.