1949-50 Horizontal Control Survey Eniwetok Atoll, Marshall Islands

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Summary of general features of the scheme Location of control points Geographic position and azimuth List of geographic positions List of directions Abstract of directions Computation of triangles Check computations of Joint Task Force Seven Survey Computatioriof geographic positicns Base line computations StatIon description and reoovery notes

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t ) fnm a second order base line !30gallua Island and southward l of coordinating local surveys Runit Island. The scheme extends northward to Eniwetok Island. The survey was for the purpose project islmds and to establish distances and : azimuths between certain installations. z Standard procedure and specifications of the U.S. Coast and Geodetic Survey Z for second order triangulation was the criteria for this survey. The geometry &@f the scheme was checked by the Los Angeles Office of thet organization before ~ afield work started and the results of observing the scheme were checked as to~~ ~~procedure in January of this year. ..% The scheme was so executti that jt can be expanded to irclude the complete ~&%toll and where possible the permanency of station loc~tions was considered. Ml < station markers on project islands were referenced. Referenclr.tgof the two stations ~ in the lagoon and on the ssnd spits south ofRunit Were not pratical. Two previous surveys have been made of the eastern portions of the atoll. As stated in the reconnaissance report of January 7, 1949 these surveys were not readily adapted to tbe requirements of this project and to expand the present scheme. The U.S.S. 13@WDITCESl?RVEYmade in 1944 was of third were necessarily reoccupied order ~ccuracy and covered the eastern ~ortion of the atoll from Igurin to T30gumbogo. The apparent purpose was hydrographic charts of the atoll. It included a base line on Runit Island and control pints on eleven other islands, also a station 5n the lagoon in the vicinity of the existing station, Coral. The geographical position of station North Base on Runit Island and the azimuth of the base line between stst,ionsNorth Base and South Base were detemined by astronomical observations. As most of the staon this survey were not on project islands and the reoccupation of its stawould have been necessary in any case for system expansion the values found e U.S.S. Bowditch Survey were not incorporated into the present survey, except that the Joint Task Force Seven Survey determination of of station Runit was based on the original geographical the latitude and longitude position of station North

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Base as established by this survey. Also, the azimuth of the line North Base-Sand The Jf31NTTASK FORCE SEWX SHNEY mde in 1947-48 and covering the eastern ~ portion of the lagoon from Aniyaanii to Engebi, consisted of a limited scheme with u stations on Engebi, Aoman, Runit and Aniysanii and station Coral h the lagoon. z The scheme was stated to be of first ozder accuracy and first order procedure was used. However, the base expansion figure was not consistent with spec~flcations& U.S. Coast and Geodetic Survey and it wati’onlybecause of the lindted extent o @of the scheme that it could be considered of a high order of accuracy.~g c> Of the seven stations inoluded in this survey, station Graflexon Acman Island +m.~ad been destroyed and the stition on Aniyaanii was of little value in expanding ~ reoccupying three of the five remaining stations. It thus was apparent that the $ expanded requirements of the present & Station South Baseof the U.S.S. survey involved re-~stablishment of a complete Bowdftch Survey was not recovered and a new station ‘Runit~lwas established at the south end of the Base-Runit became the ba~e ltie of this survey. The geographical pxition of station North Base and island. The line l$orth the azimuth of the line North %ase+and as established by the U.S.S. Bowditch Survey were accepted and became the origim of posi.tier)and azimuth. “Although the original azimuth observations were made from station North Base to station South Base an examination of the corIcctions obtained for the angle in the U.S.S. Bowditch trizngulatiorisshowed that but little accuracy ~ould be lost by accepting the azlm@b of the line from station North Base to station Sand hs the basis of azimuths for the survey. Therefore it was considered that reobservation for azimuth was not justified. The line North B6se-Runit was measured to first order accuracy and the azimuth of the line was computed from its relation to the line R. Base-Saxxl. The computations involved in establishing the azimuth of this new base line have been checked and are included here for reference purposes.

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A copy of the Report of the Engineer, Joint Task Force Seven, Part 2 was made available to us and has been of great assistance in planning and exeouttig

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Location of Control Points the requirements of the present project, a horizontal net has been consisting of fifteen stations, including ffve stations of the f Joint Task Foroe Seven Survey. Two of these five were original stations of the ., z U.S.S. Bowditch Survey, and an additional station of that survey on Eniwetok z “ is also included. Stations are located so that all project Islands are tied in ‘ 2$ directly to the scheme or can be tied in by local.triangulation. A new station 0% in the lagoon off the south end of Runi.tIsland was established to strengthen +.Q, Where practical, stations have been given the nameof the island onwhioh $ “~ they are located. This was done to simplify reference to these stations. Some e of the U.S.S. Bowditch and Jotit Task Force Sewn stations have been rammed 3 and reference to this is made in the station recovery notes. The stations of = the survey and location are as follows: Yhoto tower im lagoon Third sand island south Of Runit south of Fhmit The islands of Muzinbearikkuj Ki.rinianand Aaraaubiru will be tied in by local triangulation. Japtan is not included in present control requirements but car be tied in by the same method if desired.

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Geographic Position and Azimuth In’the interests of economy and because we concurred with the Joint Task I%rce!,.“”{ S&ren Survey that l~ttl’eacouraoy would be 10S+C,it was our intention to accept x ~Lj@e g~graphical POSitiOtiof station Worth Base and the azimuth of the new base ~ ~~hld not be acaap$d. as tie point of OFf&@ of the present survey. A oozqnxted found. TI& clifferenee may have been caused by physical displacement of the to station Runit to establlab a base 1ine for the present survey. The geographical Coral =o@d be accepted for positfon and azitith as the llmited e&ent of the ad--.. jus&ents 411volvedwould not appreciably effeet the accuracy requirements of this

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The observing party all locattons involved was made and markers set for the ~ Actual observing on this survey started in October, 1949. consisted of an observer$ recotier and a varyfng number ~~ of light tenders. The party was quartered on an L.C.T. which moved to cmven-= lent points in the lagoon as required. An L.C.11.and a DUKW were used for traqshaving landing strips. Four Bilby ste~ towers were available for the survey and were stations as the survey progressed. Where low towers could be used moved to new strmted of wood. The towers ware adequately bra~ed and little vibration was experienced~ All observing was at night using lights for targets. A Ufld T-2 . theodolite was used,for observtig and found to be ve&&ati.ufadory. Ehmefif. ‘:; ficulty was experienced with the efierior lighting probably due to moisture. Station lights were constrmted f’rcmU.S. Navy battle lamps by instslltig a reo-, stat. This made it possible to dim the Mghts to oorreot intensity and thsy made portable rad~os. Considerable time was saved by this means of communication as the light intensity could be adjusted instantly,and changes’in plans could be &nsmitted to all personnel involved. This was often necessary due to weather conThe observing was done at a period of the year when high wind velocity was experienced. Some time was lost considerable rain and due to weather both in being unab le to get to the stations and poor visibility while occupying the Water transportation was adequate but necessarily slow and the personnel ware usually away from the base of operations foutieen to sixteen hours.

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Travel after dark in the lagoon was considered dangerous and the personnel were distributed before dark and picked up after sunr~se in the morning. Observing procuiure cousistqd of adjusting the intensity of the statiom lights to the minimum which could be observed thereby obtaining a small targer considering the distance involved. This was done as earlyin the evening as sufficient Due to weather it was Wening. From two to and froIso~e to three sets of six positions each were obeerved. sometimes only possible to complete one satisfactory set in an five hours were spent in observing. When results obtained were within the specifications of the U.S. Coast and Geodetic Survey no attempt was made to obtain further refinement. The strength of figures obtained for the net was an RI of 74.4 with a UELXim A mximum triangle closure of 2.5 seoonds and C!Iaverage closure Of 103 se~~s was obtained with the maxismm of 8 seoonds for one triangle average closure allowed the two stations, Eorth is a broken base consistingof four Base and Runit. This was necessary and 3 seconds for the due to the configuration of the island. Traverse Station Runit of the Joint Task Force Seven Survey is an angle point In this traverse and was also included in the former traverse. Standard procedure of the U.S. Coast and Geodet$c Survey for second order base line measurement was used. Angles were measured with the Wild T-2 theodolite and the measurement was made with three Lovar tapes using thermometers and stretcher apparatus of an approved type. The calibration certiffoates of these tapes are included In the record of the survey. were set at fifty meter intervals for chaining so that in completing the fomard and bsckwafi used in each direction. the velocftyof the wind break in order to obtati at thfs period of the points and the tapm were measurement all three year it was necessary to accurate results. This consisted of a thirty

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six inch strfp of canvas approximately fifty five meters long which wes held parallel to the line as each measurement was made. The computed probable error of the total measurement is 1 part in 6@,000. allowable maxi.mumprobable error is one part in 500,000.

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LIST OF DIRECTIONS STATION AOMOIII (Aomon Trav. Sta.) DATE 3A7150— CHIEF OF PARTY COMPUTED BY ‘H OBSERVED I ECC. I SEA LEVEL CORRECTED DIR. ADJ. DIR. DIRECTION RED. / RED. ZERO INITIAL of lights or instrument Observations taken from 40 foot steel tqwer

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HOLMES a NARVER ENGINEERS JOB NS. 640 , LIST OF DIRECTIONS STATION BOGA DATE 3/17/50 CHIEF OF PARTY W COMPUTED BY LSH ECC. SEA LEVEL 1 jNo eacentrioi y of lights or $nstrumen at this e from 40 fook steel t er Referenae roars are bronse di~ka in 00 rete blo

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HOLMES & NARVER ENGINEERS JOB LIST OF DIRECTIONS from a 15 foot wood tow re bronze diskq In ooncr

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CHIEF OF PARTY LSH COMPUTED BY ‘H OIRECTION / REO. I RCO. NO ocoentrioit of lights or ipstmment at this s Observations m~de from a 14 foot wood clroular COIIO ete 00U

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HOLMES 8 NARVER ENGINEERs JOB N!?. 640 LIST OF DIRECTIONS CHIEF OF PARTY -LSH COMPUTED BY ImI l OBSERVED STATION CORRE~ED DIR. from 40 foot +91 towe e bronze disks in concr

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HOLMES & NARVER ENGINEERS JOB N:. 640 LIST OF DIRECTIONS CHIEF OF PARTY MH . Light was euue Light was at t Iken from eoeentpic stati n ue station for observati n from Pa: made from a 40’foot ste 1 tower

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HOLMES & NARVER ENGINEERs JOB N:. 640 LIST OF DIRECTIONS STATION NORTH BASE CHIEF OF PARTY ~H FNo eccentricity f lights or in PObservations mad from 40 foot Referenae marks re bron~e disk set in r f ledge

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HOLMES & NARVER ENGINEERS JOB W. 640 LIST OF DIRECTIONS STAT ION PARRY CHIEF OF PARTY ~H ‘ of lights or de from 25 foo~ wood bI are brmnze di lcsin

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CHIEF OF PARTY ~H f lights or Instrument a n from 16 foot wood tom re bronze disks in concr RED. ZERO INITIAL

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LIST OF DIRECTIONS OBSERVED STATION ] SEA LEVEL ~ CORRECTED OIR. DIRECTION I RED. 1 RED. t zERo l~lTIAL Observations m , e from a steel tripod 10 ~feetabov~ tide level No referenoe malks set at this station

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HOLMES & NARVER ENGINEERS JOQ N!?. 640 LIST OF DIRECTIONS - CHIEF OF PARTY ~~ Reference mark are bronse dieks in mm

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HOLMES 8 NARVER ENGINEERS JOB N:.640 ABSTRACT OF DIRECTIONS CORR. FOR ECC.

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HOLMES 8 NARVER ENGINEERS JOB N5?.64C) ABSTRACT OF DIRECTIONS CORR. FOR ECC.

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HOLMES 8 NARVER ENGINEERS JOB N:.640 ABSTRACT OF DIRECTIONS STATION CORAL COMPUTED BY ‘5H DATE Ocf, 26, /949

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HOLMES 8 NARVER ENGINEERS JOB NS,640 ABSTRACT OF ill RECTIONS POSITION . STATIONS OBSERVED 1 CORR. FOR ECC.

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HOLMES El NARVER ENGINEERS JOB N2.640 ABSTRACT OF DIRECTIONS POSITION . STATIONS OBSERVED CORR. FOR ECC.

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HOLMES 8 NARVER ENGINEERS JOB N: 640 ABSTRACT OF DIRECTIONS OBSERVER EPC. CHECKED BY w ‘~ INST. ~ltd 7-2 CORR. FOR ECC.

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HOLMES 8 NARVER ENGINEERS JOB N:.640 ABSTRACT OF DIRECTIONS, \ z STAT ION ISLET CORR. FOR ECC.

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ABSTRACT OF DIRECTIONS POSITION. STATIONS OBSERVED Coral Aomon 5c7nd I Perry CORR. FOR ECC.

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HOLMES 8 NARVER ENGINEERS JOB N:.640 ABSTRACT OF DIRECTIONS CORR. FOR Etc. ~

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HOLMES 6 NARVER ENGINEERS JOB N:.640 ABSTRACT OF DIRECTIONS CORR. FOR ECC. --”-’-?-

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HOLMES 8 NARVER ENGINEERS JOB N:.640 ABSTRACT OF DIRECTIONS CORR. FOR ECC.