CHAPTER Ii, SECTION 1 SURVEY. Survey activities were directed by a Department Head located at Elmer and assisted by Assistant Department Heads, supervising field survey and office work at Eniwetok and Bikini Atolls. During Operation HARDTACK, an Assistant Department Head wasalso located at Johnston Island. The organization of the Survey Department consisted of field parties, normally four men each, supporting office personnel, in- cluding Computers and Draftsmen, and Supervisors for each location. Personnel increased from 8 on 31 December 1956 to a peak of 73 on 11 March 1958. Surveying activities during the interim and build-up phases included topography at Rongelap, Truk, and Ponape; boundary surveys at Rongelap, Nauru, Tarawa, Truk, Ponape, Utirik, Ujelang, and Kusaie; an entrance channel reconnaissance at Taongi; and “as-built” and con- struction surveys for rehabilitation of Rongelap Village. During the operational period, surveying activities were concentrated on PAC construc- tion at Elmer, David, and Fred, Scientific Station and barge location, horizontal and vertical control, topographic mapping and plane table surveys, hydrographic mapping, Microbarograph Stations, barge and hull motion studies, tide studies, and rainfall and temperature data collection. The transfer of the ABMA program to Johnston Island resulted in a requirement to determine precise measurements impractical to obtain by conventional methods. To obtain this information, a Tellurometer system was purchased. Later developments cancelled the require- ment for these measurements. However, the Tellurometer system was utilized at Eniketok and Bikini Atolls. The Tellurometer system de- termines distances by measuring the travel time of high frequency radio waves and is capable of accuracies of the order of 1 part in 100,000, or better. The range of the system is stated to be from 500 feet to 35 miles. The capabilities of the Tellurometer system are such that many of the precise surveys, now performed by triangulation requiring night operations, can be accomplished in the daytime. Also, this system is not affected by high winds, rain squalls, or light refraction. Horizontal Control — Eniwetok Atoll The 1957 expansion survey established new second order stations on Sites Yvonne, Sally, and Gene and third order stations on Sites Glenn, Henry, James, and Keith. The triangle closure to include Station Lantana on Site Glenn exceeded the allowable closure limits; however, the triangulation towers were damaged by a (Neg. No. W-V-94-3) Figure No. 2-13. Elevation Check at Station 1312 — Janet. storm before they were completely rechecked. An evaluation of the tentative results indicated the values to be within a tolerance of one part in 5000. Therefore, it was decided to defer re- observation of the triangulation towers until more precise values were required for the station. Horizontal Control — Bikini Atoll A requirement was received to determine the relationship of two sites to within a tolerance of one part in 25,000. An evaluation of the Bikini network was made to determine if this requirement could be met without extensive additional triangulation to first order specifications. This evaluation indicated that if the full capacity of the net were obtained by an adjustment by the method of least squares, the net, while not to first order specifications, should be well within the required tolerances. An adjustment was applied by the method of least squares which indicated that the prob- able error in a direction, as computed from the adjustment, was 0.81 second. Only minor corrections were made to directions and distances as determined by the side equation adjustment. The 1953 Station Charlie on Site Charlie was recovered in 1957 and its distance relation measured to Station Chuck. Based on the adjusted values for these stations, a discrepancy of 0.15 foot was found between the computed and the measured distances. A check survey of two large quadrangles was completed in 1957 based on thefixed locations of Station Yoke, Oboe, Nan, and N. How, Page 55