CHAPTER II, SECTION 1A 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 bejustified. The origin of plane coordinates N103,872.0, £128,879.0 was taken at Station Air of the US Navy Survey which has also been adopted as the origin of geographic position. 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 N88-00-01.4E. The adjusted length of the line USN-Air to USN-Enyu, as determined by expansion 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. The adjusted length and direction of the line Oboe-Nan (USN-Enyu) as determined from its relation to the line USN Air-USN Enyu was adopted as the initial line for computation of geodetic and plane coordinates for this survey. TRIANGULATION ADJUSTMENT. The com- puted closing error of the triangulation net, be- fore 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 well 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 station 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, satisfied 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 requir- ed for design of project features were initiated 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. Surveys were initiated on the other project islands as Page 2-24 rapidly as personnel and transportation facilities were available. The location of the high tide line of an island wasthefirst objective, followed by more detailed surveys of the interior of the islands where required. HIGH TIDE LINE SURVEYS. Thefirst requirement for site planning was to determine the configuration and extent of the land areas of the project islands. The procedure was to establish a third order traverse around the perimeter of an island, the elevations of the high tide line by relation to a preliminary vertical datum, and locate this line by stadia observations from the traverse points. The results of the survey were plotted, thereby obtaining an outline of the island. TOPOGRAPHIC MAPPING. Assite planning progressed, more detailed surveys were require to determine the relative elevations and location of terrain conditions which would influence design. This work was accomplished by plane table mapping, generally at scales of 1” to 50’ or 1” to 100’ and one-foot contours, or by profiles and cross sections of an area. 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 under- water 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 Departmentin locating channel markers and mooring buoys. 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 a barge around a fixed point. To determine this information, observa- tions 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 azimuth of waves were measured and a record was kept of the direction and velocity of the wind. WAVE AND CURRENT STUDIES. Support was given to representatives of the USN Hydrographic Office in determining wave and current studies within the lagoon and seaward from the channels through the reef. A survey party assisted by locating the observation points by sextant angles to shore stations. CHANNEL LOCATION. Support wasalso given a USN Hydrographic Office group in determining the locations of channels within thelagoon for deep draft vessels. The wire dragging of these areas was located from controls established by this department and department personnel assisted in the operations.