CHAPTER II, SECTION 1A sions. It consisted of 16 stations covering the eastern portion of the Atoll from site Alice to site Fred and included five stations of the previous surveys. As it was determined that Station North Base had been disturbed, it was necessary to measure a new base line, North Base #2-Runit, to second order accuracy. The network expanding from this base line was executed to second order specifications and procedures of the U. S. Coast and Geodetic Survey. The geographical position of Station Runit and established and is common to all stations within the limits of the Atoll. The origin of coordinates is a plane through triangulation Station Coral with assumed value of N 100,000 — E 100,000 at this station. A true meridian through this station was used as the basis of bearing and was determined by computing through the base expansion figure from the adopted azimuth of the Runit base line. mined by the JTF SEVENsurvey, were adapted as the origin of position and azimuth. A detailed description of the survey was included in the completion report for OPERATION GREENHOUSE, Volume V. quirements included precise surveys to determine the interrelation between Scientific Stations within local areas. The relation to zero of some stations was determined to first the azimuth of the line Runit-Coral, as deter- 1951 EXPANSION. An expansion of the survey was necessary to meet additional requirements SPECIAL SURVEYS, GREENHOUSE AND IVY OPERATIONS. Horizontal control re- order traverse specifications, and precise meas- urements were taken to determine the blast effects on certain structures. An unusual feature of the survey program was the alignment re- which could not be anticipated earlier. Several quirements of the 203 series stations. This in- lation, and photo tower and zero station locat- tolerance of 1:25,000 and establishment of a additional islands were located by local triangu- ions were determined. Local control traverses were established on all project islands. The accuracy of these controls depended on the scientific requirements and was generally of third order. The zero lines and some traverses for location of instrumentation were established to first order traverse specifications. An independent plane coordinate grid was established at each of the zero areas for location of Scientific Stations. While satisfactory results were obtained, it brought out the desirability for an over-all atoll grid. 1952 EXPANSION AND ADJUSTMENT.Requirements for OPERATION IVY resulted in expansion of the scheme to include the entire Atoll. Some stations of the scheme had been destroyed by test operations and additional stations were required. Fifteen stations were established, replaced, or more precise values determined. As the expansion permitted closing the survey around the Atoll to the Runit base line, a check on the previous work was obtained. The closing error of the survey, before adjust- ment, was determined to be approximately 1:25,000. An additional check was obtained by inclusion of the zero line traverse in the FloraGene area. This indicated a closing error of approximately 1:70,000 before adjustment of the adjacent quadrangle. In order that the values of a station would remain the same, independent of the direction of computation through the net, an adjustment was applied to the triangulation figures. This consisted of a side equation adjustment which resulted in slight changes in the values previously reported but of little consequence in computations made from the earlier data. PLANE COORDINATE SYSTEM (IVY GRID). A plane coordinate system was cluded measurement of a zero line to a linear 9,000-foot line of sight to a tolerance of plus or minus one quarter inch. Vertical control was accomplished by establishing a series of bench marks by precise differential leveling and applying a correction for curvature of the earth’s sur- face. Horizontal control stations were established with precise equipment by night operations to avoid heat wave distortion and refraction and procedures were developed to produce the re- quired accuracy. The alignment of the stations was accomplished by offset measurements from these controls to a previously established working point on each station. 1954 EXPANSION (ENIWETOK ATOLL). No major expansion of horizontial control was required in this area for OPERATION CASTLE. The locations of Stations 60 and 2211 were determined to second order by local triangulation from stations of the primary network and con- nected by a first order traverse. The location of Station 10 was determined by expanding from local controls which were recovered in the general area. The accuracy of location was consistent with scientific requirements. Existing horizontal control was satisfactory for the location of all other Scientific Stations. Figure 2-3 and Tables 2-1 through 2-12 list the survey expansion geographic positions, plane coordinates and hori- zontal control stations. HORIZONTAL CONTROL - BIKINI ATOLL The requirements for horizontal control at Bikini Atoll were essentially the same as for the network previously established at Eniwetok Atoll. The requirements included a primary net- work established to second order specifications of the U.S. Coast and Geodetic Survey supplemented by third order stations in locations of lesser importance. Page 2-7