Horizontal Control - Eniwetok Atoll M.i. 1957 Expansion

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HORIZONTAL CONTROL - ENIWETOK A network of horizontal control stations was established in 1949-5C to cover the eastern portion of the Atoll. It consisted of a primary net o; second order triangulation stations, supplemental with third order stations at locations of lesser Importance. Standard procedures of the U.S. Coast and Geodetic Survey were carefully followed in executing the survey. Fxpansion surveys were completed in 1951, 19529 1955 and in 1957 to establish additional stations and replace stations destroyed by test operations. The network now encompasses the Atoll and includes sixteen statiom to second order specifications and eleven to third order accuracy. Some features of two previous surveys were utilized in the ;’$’ scheme.* A third order survey had been completed in 1944 by the : USS Bowditch to control hydrographic mapping of the Atoll. This s was followed.in 1947-48 by a second order scheme of limited area z-w by the U.S. Coast and Geodetic Survey. As the distribution of the ;2 existing stations of these ,surveysdid not meet project require- :,$ ments, and one end station of the base line had been destroyed~ a ~~ substantially new and stronger scheme was necessary which could be %.s expanded as required. o A base line for the net extended from station *Q YVONNE to a new station NORTH BASE #2 at the north.U RUNIT on site end of the ~ island . Station RUNIT was common to both the USS Bowditch and ~, 2, the USC & GS surveys. The base line was established to standard

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procedures of the U.S. Coast and Geodetic Survey for second order base line measurement. The computed probable error of total measur/rnentof the line was one part In 648,000. The allowable maximum probable error for second order base line measurement is one part in 500,000. The geographic position of station RUNIT as determined by the USC & GS survey was adopted as the origin of geographic position. The azimuth values of this survey for the line, station RUNIT to station S~TD were adopted as the origin of geodetic azimuth. The probable accuracy of the adopted values for position and azimuth are not known, but it was considered that the accuracy was conslstant with project requirements at the time, and the expense of further refinement could not be justified. * g The computed closing error of the survey before adjustment ~ was determined as approximately one part in 25,0C0. An additional 4 check was obtained in 19~2 by Inclusion of a first order traverse # ~-. in the FLORA-GENE area. This indicated a closing error of approxz.: imatelyone part in 7(2,000before adjustment of the adjacent *W0: quadrangle. In order that the values of a station would remain e> the same independent of the direction of computation through the—..—, J?u net, an adjustment was applied to the triangulation figures. 9 u This consisted of a side equation adjustment which resulted in !2 slight changes in the values previously reported. “’i A plane grid was established In 1952 which was common to the a entire Atoll, and from which the inter-relation of structures and areas, and their positions could.be specified by plane coordinates.

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Due to the limited area, the slight additional refinement obtained by computing a Transverse Mercator Grid.would not have been The origin of plane coordinates, N 100,000, E 100,000, was taken at station CORAL and the basis of bearings was a true meridian through this station as computed through the adjusted figures from the line, station RUNIT to station SAND. The 1957 expansion survey included establishing new second order stations on sites YVONNE, SALLY and GENF and third order stations on sites GLENN, HENRY, JAMES and KEITH. The triangle closure to include station LANTANA on site GIENN exceeds the allowable closure limits. However, the triangulation towers were damaged by a storm before re-observing could be accomplished. As an evaluation of the observing results indicated the values to be within a tolerance of one part in ~,000, it was decided to defer the re-observing until such time as more precise values are required for the station.

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COMPUTATION OF TRIANGLES SPHERICAL PLANE ANGLE sTATION OBSERVED ANGLE EXCESS AND OISTANC

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DESCRIBED BYW. Creasman MARKED 8 Y. H.M.J. Enlwetok Atoll Thisstation was establishedas a secondordertriangulationstationin the Thisstationis locatedappro@matelyat the centerof the bland and 12jfeet The station mark 5.sa standard H & N brass cap set in a concrete filled55 This station is the western end of the Wene-Helen-Irene ~ first order traverse. Bucks #1 and #2 are 4ntiN posts set in concrete with a punched aluminum strip fastened to the top. The Strips are stamped with the buc)cnumber.

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This station was established as a third order triangulation station in the Atoll ‘ Control Net by the Holmes & Narver 1957 Expansion Survey This station is located on the north east portion of the islakd approximately 50 feet south of the lagoon hightideline. The stationmarkis a standardH & N brasscap set in concrete1 footbelow driven flush with the ground surface. They-are P.I.’s b the Island twographic control traverse.

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FIELO BOOK NO. PA GE, DATE, June 195? Marshall Islands ELEVATION OF MARK 6e76 DETAILED DESCRIPTION OF STATiOAI. This station uas establlshti as a third order triangulation station In the Atoll Oontrol Net bg the Holmes & Rarver 1957 ExpansionSurvey. Thisstation is looat.edon the north east portion of the i8h@ apprafite~ 30 feet fromthe lagoonhightide line. The stationmrk is a standatiH & N tmasscap setin concreteflushwiththe driven flush with the ground surface. They are P.I!s in the Island topo-

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ELEVATION OF MARK This station was established as a third order Traverse Station in the AtoU control net by traverse from Trian@ttin Station Henry as a part of the Helms & Narver 1957 Expaneion Survey. Thisstation is located approximate=35S feetfromthe eastend of the islandand 45 feetfromthe lagoonhightidetie. , The station mark is a standard Holmes &,Narver brass disc set in concrete

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L)ESCRIPT!ON OF TRIANGULATION STATION Eniwetok AtollFIELO BOOK NO PA GE. DATE June 1957 MarshaU Islands ELEVATION OF MARK This station was establis~d as a third order trlanguhtion station in the Atoll ContrQl Net by the Robs & Narver 1957 Expansion Survey. This station Is located on the north portion of the f,sl.and, apprub~ 40 f-t from the lagoon highttdellne, The stationmark is a s~d H & N brassoap set in concreti1 foot below

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The station mark is a standard H & N brass cap set b a concrete filled 55 This station is at the north end of the ~Yvonnen first order traverse. This R.M. is an angle point on the ltYvonne”firstordertraverse,

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NAME OF STATICIN SALLY . SITE SALLY F)ELD BOOK NO: PA GE; DATE 5~13~57 Marahall Islands :jg This station was established as a 8eCOIId order triangulation station in the f:!: Atoll Control Net @ the Holmes & Narver 1957 Replacement Survey to replaoe @ tr~angulation station Aomon which was disturbed during Operation Redw6mg -! This station is looated on the south east portion of the island, approximately “q .5 350 feet from the lagoon high tide line. ‘:Ja;~ The station mark is a standard H & N brass oap set In a concrete filled 55 4:-1 h This station is a part of the Wallylt first order Traverse. Bucks #29$ 30 and 43.are 4%c4W posts set in concrete with - aluminum strip z on the top with the buck number stamped on it. They are chaining bucks in a the Sally First Order Traverse.

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This station was established as a second order triangulation station in the Atoll Control Net by the Holmes and Narver 1957 Replacement Survey to replace Rujoru, which was disturbed during operation Redwing. The station mark is a standard H & N brass cap set in a mass of concrete encasing the top of a number of steel marked only by a center punch mark. This station is located approximately and 1~ feet from the easterly end of rebars driven to refusal. It is 90 feet from the ocean high tide line No reference marks were set at this station when it was established.