Operation Castle, Project 7.1, Electromagnetic Radiation Calibration, Pacific Proving Grounds, March - May 1954 (Deleted)

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ELECTROMAGNETIC RADIATION CALIBRATION Headquarters Field Command Armed Forces Special Weapons Project Sandia Base, Albuquerque, New Mexico This is an extract of WT-930, which DATA as of this date. Extract version prepared for: Defense Nuclear Agency Approved for public release;

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OPERATION CASTLE, PROJECT 7.1, ELECTROMAGNETIC Headquarters Field Command Armed Forces Special Weapons Project Sandia Base, Albuquerque, New Mexico Approved for public release; unlimited distribution. This report has had the classified information removed and has been republished in unclassified form for public release. This work was performed by Kaman Tempo under contract DNAOOl-83-C-0286 with the close cooperation of the Classification Management Division.of the Defense Nuclear Agency. Electromagnetic Radiation Calibration A total of 17 stations, one close-in (320 km from Bikini and 23 km from Eniewtok) ant the balance at distances, were operated for the AFOAT-1 electromagnetic experimental effort. Seventy-four sets of data were obtained from a possible total of 102. Of the remaining 28 sets, no data were obtained because equipment was not in operation, records were not readable, the alert notifications were not received, signals were not discernible, or equipment malfunctioned. Do LDITIDN 01 f NOV 66 IS OWOLETE UNCLASSIFIED

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This report has had classified material removed in order to make the information available on an unclassified, open publication basis, to any interested parties. This effort to declassify this report has been accomplished specifically to support the Department of Defense Nuclear Test Personnel Review (NTPR) Program. The objective is to facilitate studies offthe low levels of radiation received by some individuals during the atmospheric nuclear test program by making as much information as possible available to all interested parties. The material which has been deleted is all currently classified as Restricted Data or Formerly Restricted Data under the provision of the Atomic Energy Act of 1954, (as amended) or is National Security Information. This report has been reproduced directly from availa'ble copies of the original material. The locations from whic,h material has been deleted is generally obvious by the*spa#cings and "holes" in the text. Thus the context of the material deleted is identified to assist the reader in the determination of whether the deleted information is germane to his study. It is the belief of the individuals who have participated in preparing this report by deleting the classified material and of the Defense Nuclear Agency that the report accurately portrays the contents of the original and that the deleted material is of little or no significance to studies into the amounts or types of radiation received by any individuals during the atmospheric nuclear test program.

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A total of 17 stations, one close-in (320 km from Bikini and 23 km from Eniuetok) and the balance at dlatancee, wre operated for the AFOAT-1 electromagnetic experimental effort. Seventy-four setrr of data wre obtained from a possible total of 102. Of the remaining 28 seta, no data wre obtained because equipment was not in operation, records were not readable, the alert notifications ~01‘8 not received, signala wre not discernible, or equipment malfunctioned. narxPw-band (about 200 cyclea) measurements wre made of the vertical field compnent. Close-in waveforms and field strengths wre recorded for all shots except the first. Signals wre received and waveforms, field strengths and azimuths were recorded at distance8 exceeding Spectrum analyses of the frequency content of the close-in waveforms confirm the theoretical conclusion that the predominant frequency becomes lowr as the yield Increases. For a nuclear wagon In the l&Mt range, the predominant frequency is about 8 to 10 kc, while in the 100&t range it ia about 18 to 20 kc. Analyees of broad-band pulaea’received at distances ahow that the higher frequencies are attenuated relatively more-end, when received at several thousand kilometers, the close-in differences largely disappear. An approximation of yield may be obtained at distances by measurement of peak field strengtha. where equipment capabilities permitted, times of detonatlon-- after allowing for travel time of the nuclear detonation signals and standard time signals ---bwre measured to vithin 2 msec, with one exTransmitting stations in the very lov frequency band wre nronitored at selected intervala. Generally, a north-south path croeelng the auroral zone sbowa greater attenuation than an east-west path of equi-

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This report is one of the reportspresentingthe resultsof the 34 projectsparticipatingin the MilitaryEffectsTests Programof interestedin other pertinenttest information,referenc:eis made descriptionof each detonation,includingyield,height of burst, ditionsat detonation,etc., for the six Shots; (2) Msc:ussionof all projectresults; (3) A summaryof each project,includingobing the MilitaryEffectsTests Program. The experimental and analytical uorkuhichthis reportetuumar~zes was performedby the staffsof the NationalBureauof Standardsand the .DefenseResearchI&oratory of the Universityof Texas. The Sferics Gperatiousstaff of the Air Weather Serviceoperatedst;mdfi very 10; by AlQAT-1, AFQAT-1 appreciatesthe effortsand close cooperationthat have characterisedthe people of the above groups workingon the problem of long Rauge Detection 3 andespecially Capt. Mack Sibr, Air WeatherServke AFGAT-1handledthe operationalmattersin a helpfuland expeditioue manner. kubers of the three APDAT-1electromagneticsi;atlonefurnished data at a difficulttime when the stationswere being put into operation in the preparationof the report.

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Yieldfmi Predoininant Prequency .................................33 1 Summary of Castle Results.................................... 19 tracerecordedon a multi-beam oscillosopeat a distant

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04 PretinentInformationon Castle electromagnetic stations. .... 17 5 Plot of selected Castle data showingthe relationshipbetwean peak field strenghtand yield on an east-westpath............23 6 Plot of seleatedCastle data showingthe relationshipbetween peak field strenghtand yield on a north-southpath ..*.......a 7 Selectedreaordsfrom Shot 1 detonatedon 28 February1954at 8 Selected recorde Prom Shot 2 detonatedon 26 IG.rch1954 at 9 Selectedreoordsfrom Shot 3 detonatedon 6 April 1954 at 10 Selectedrecords from Shot 4 detonatedon 24 April 1954 at 11 Selectedrecords from Shot 5 detonatedon 4 IJQ 1954 at 12 Seledtedrecordsfrom Shot 6 detonatedon I.3May 1954 at 15 Spectralintensity,as a functionof frequency,for Shot 3 aa showingthe relationshipbotueenyield aad predaninant 17 Plot of the field strengthof NSS ae measure+by DRL at 18 Plot of the field strengthof NSS as mearuredby DRL at Thule, 19 Plot of the field strengthof NPH as measuredby DRL at Thule, 20 Plot of the field strengthof NPM aa measuredby DRL a% Austin, 21 Plot of the field strengthof NSS aa measuredby DRL at Austin,

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ELECTROMAGNETIC RADIATION CALIBRATION In order to gain maxFmuminformation on nuclear detonations as determined from the electromagnetic pulse received at distances, there are two fundamental problems; first, the discrimination of nuclearweapon pulses from natural atmospherica and second, the determination of the maximuminformation on the source itself and external conditions at detonation time, from the characteristics of the selected pulse. The 7.1 Castle project offered an opportunity to monitor detonations of nuclear devices of known composition and characteristics. More specific objectives can be sumnw ized as follows: 1. -Determination of pulse character gation become apparent. 2. Determination of @se character parameters such as distance, time of day, 3. Measurement of field strength. 4. Explanation of the causes of the as a function of external and ionospheric conditions. 5. Relation of pulse occurrence to sequence of events during the 6. Relation between nuclear-ueapon characteristics and pulse characteristics, both close-in, and, insofar as possible, at distances. 7. hcperirrentation with prototype surveillance equipment. 8. Measurement of azimuthal errors in direction-finding equipment. 9. Determination of times of pulse reception to within 1 msec in AF'OAT-1has supported experimental measurements of the pulse emitted at the time of a nuclesr detonation during each series of'atcmic teats beginning tith Buster-Jangle (Autumn, 1951). As a result of these experiments (References l,2,3), the following can be stated with some 1. There is an electromagnetic pulse loss than 100 psec long emitted at the tkae of a nuclear detonation, At a distanceof 20 h from the generatingsource,the field may be a few hundredvolts per meter. There is a general relationshipbetweenkilotonfield and the componentof the electromagnetic field. The emitted frequency spectrum extends from about 2 kc or tc a few megacycles, but the msln components are in the region

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5. There is an approximateinverserelationshipbetreeafield and 6. Azlses reaelved close-in (1.0. approximately 20 km) exhibit vey short rlae t$mes (less thsn a microsecond) in a negativedirection (i.e.ths eleotricfleld vector Is downward), 7. The pulse 1s predomlrmtly vertically polarised. 8. Close-in reoeptlon lndlcatea that certain nuclear-weaponcharaoteristlcrrcan be determinedfrom puke fine structure. able at distancesin exaess of 1,COC km. 10. The groundvave Is generallynot deteotablebeyondabout 1,500 Ipafrom the sourcebecause the Ionosphericsky wave reflectionspredomIl. A fix of the sourceof the pulse can be obtainedwith dlrection-findingequipnent;observedazimuthalerrors to date using equip ment tuned to 10 kc have been between0 and 9 degrees;most errorshave been less than 3 degrees. 12. At distances,the pulse ie extendedto approximatelyten times Its close-inlength. This is the resultof multiplemivsls by varlous paths, each characterieedby one or mre ionosphericreflection. 13. Close-infine structuredisappearsduring sky wave propagation All stations,both close to and at distancesfrom the detonation pulse. Close to the explosion,attenuatorswere--sometimesneeded to all places,the pulse (in no case greaterthan 1 msec in length)was icallywith eitherplate camerastriggeredby the pulsesor by atrip film cameras started manually just before detonationtimes. titularlyat distantkations where the energywas sometimesno greaterthan the noise, relianceat all stationswas placedupon timing 0rGDR (Rugby,England). To furtherassure a common time base, both mitter such as NSS (Annapolis,Maryland). This film was used for further correlationfor Instanceswhere fadingaffectedreceptionof UUV but did not affectreception of the high-poweredlow-frequencyNavy pulses coordinatedwith a world time station. The nuclear4evicepulse and timing pips v~re presentedon differentbeams of a multi-beamoscilfocal Timing Annex A of Reference3 has a detailedaccountof the Iktlonal Bureiu of Standard8 (NBS) local timingunit. A typical time record fkom a close-inet,ation is shown In Figure 1 and one from a

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distant stationIn Figure 2. Times of detonationscould be read from the fIlma to less than a milllsecond;howver, the uorld time at any stationvaa limitedby the accuraayof eatlmatesfor propagationtime of the nucleardevicepulse, the timing pulses,oi both. Effectively, this limitedaccuracyof world tlmea to about 21 awec. device signal aa pickedup on the broad-bandreceiver. The lover trace Figure 2 Typical NBS narmw-band field strength tracor,with a timing trace recordedon a

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shows the WWVHsignal and local synchronized time ticks superimposed. Note that the nuclear-device pulse was also picked up on the WWVHreceiver. The specific second can be determined by counting MJVHsecond marks with reference to the missing 59th mark. Time In minutes and hours is noted from a chronometer synchronized with WWVHand the start of the camera. Detonation time from the record show in Figure 1 was 28 February l&$:59.3962; with corrections for propagation times of the National Bureau of Standards Cloge-Cn Station. At the cloee-in site, a vertical antenna 0.6 inch in diameter and 2 meters long VBE used and located about 60 meters from the recording equipment in order to minimize distortlon due to radiation. At the base of the antenna a cathode follower fed a coaxial line to the recording instruments which consisted essentially of several oscilloscopes set at various sweep speeds and gains. At close distances (320 km) to ground zero, pulees were strong (several volts per meter) so there was no concern with interference from natural sources or transmitting stations, Consequently, the bandwidth of the pulses was limited only by the oscilloscopes. This- limit was about 40 MC for one type of oscilloscope used and about 13 MC for the others. The lov frequency limit vas about 160 cps. A block diagram of the close-in waveform lnstnzmentation is given mtant Statio At distant points operated by NE3 and the Defense Research Iagiatory (DRL) 30.foot vertical antennae with standard cathode followers were u&d. Naxxw-band (about 200 cpa) and broad-bend (about 1 to 70 kc) recordings uere made. A ground mat 50 feet square vas used at each location. The NBS narrow-band field strength traces, with a timing trace, were recorded on a multi-beam oscilloscope, as shown in Figure 2. Another oscilloscope and camera recorded the broad-band pulse. The DRL stations recorded the broadband waveforms. The Air Weather Service (AWS) used a crossed-loop goniometer and recorded azimuths. In addition to other equipment, all distant NDS and DRL stations employed one standard recording channel with the same electrical characteristics. This channel, fed by a cathode follower, used a standard amplifier with a flat response over about 8 to 20 kc, and a gain of about 1,000. Reports by NBS (Reference 4) and DRL (Reference 5) ehould be consulted for further details. The Air Weather Satice operatea a net of lowfrequency (10 kc) thunderstorm areas as an aid to veather forecasting. The equipment consists essentially of tn> ldentlaal amplifiers each fed by identical loops, one oriented north-south and the other east-west. The output of one amplifier is connected to the verticsl.plates and the other to the horizontal plate6 of an oscilloscope. The voltagea add vectoriallp end the oscilloscope presentation shows a line indicating the direction of afilval of the pulse uith a MO-degree ambiguity. To remove the ambiguity, a vertical antenna receiving the eleotria vector and driving the grid of the cathode ray tube through a third identical amplifier can be used to cancel a portion of the osallloscope presentation. The aaimuthal flashes on the oscilloscope face, together with 0.1~second and

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tlon-findingatatlonsrlmilarto the deecrlptionabove but with a wider Force Base, Bangor,&be and Austin. Texas 80 only signalsin a preing Ground was placed In a trailerand chippeda8 deck cargo. The contained all the equipmentexcept that for determiningworld times of eastern portionof Bikini Atall, and acro8s the lagoonfrom the detonaters on Pamy Ieland,Eniuetak Atoll. Becauseof the expectedhigh yield of Shot 1, the equipmenton &yu wa8 not manned but wae actuated by an Edgerton,Gemeshaueen and Crier (EGG) relay timw. The radioactivedebrir f'ma Shot 1 driftedover the trailer,ma3dng it impO88ibleto enter the area after the detonation until the debrirrhad decayed to a mmonable value. After a week the traileron Enyu had cooled 8ufficientlyfor handling,80 all equipment ~38 manned for the b&me of the Bikini shots. For Shot 6, which was onRunitwa8 unmannedbut wa8 actuatedby an EGG relay timer,, PlagIIetiCstations,the agency responsiblefor the measurementsat each place, and the distanoesfYom each stationto Bikini and Eniwetok. For the morstpart for dietant etations,location8alreadyin use by NBS, DRL, AWS and AIQAT-1uem utilized. At Shemya, Thule and Kirlcnewton, attemptto get 80~~ idea of the propagationdifferencesdue to a daylight path, a dark path, and auroral zone tramnission. 8chedule,in order to obtain Informationon varioustrammission path8 Alert Notlficatiopg The experimentalequipmentlnstalbedat the

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Pigllre 4 Partlnent inromatfon on Castleelectromagnetic etatlolla qmxmoring agencies; and appmxlmts distances, ln Idlometere, MEi, National Bureau of Standarde; DU, InformatIon includes station locationsj

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recordingtime (In some cases, a few seconds). In order to coordinate Wits. The messageswere In code when scheduleInformationwas sent. In additionto schedulechanges,the alert communicationcode was wed to give estimatedfield strengthsfor the variousshots and thus assist Lou-freauencvInterferencs.The distantstationsat Fort Belvolr, (16 to 20 kc) that would interferewith broad-bandrecordingsof a times. For securitypurposesthese transmitterswere also frequently taken off the air at other than shot times. There was a tital of 17 stationsparticipating,althoughfor any one shot no more than 15,stationswere in operation. A annmaryof the resultsat the variouslocationsis given in Table 1. The detonationtime was determinedfrom the timingequipmenton One of the means of locatingthe nuclear-devicepulse when recorded at distancesfrom the test site is by knowledgeof the time of det one exception,was uithin 2 msec of the Parry Islandtime after corrections for propagationand WV times were made. Some equipmentdid not have the capabilityof resolvingtime to withina few milliseconds,as indicstedby asterisksin Table 1. Azimuthalerrors are generallywithinthe error experiencedwith this type …