Aerial Tracking of Fallout by VP-1 (Fallout Charts) Operation Redwing

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Tbe objectives were tcx (I) luvey the gamma radiation from fallout-contaminated ocean areas by means of lerial detectors and (2) from the lerial detectors make air-absorption measurements so that the data might be related to the ~f rates at S feet abve the sea. ~~ Y4aircmft that mrveyed the ocean areas of expected ordinated all atr and sutiace ~dtatton-survey lctivities to insure complete coverage of tbe fallout area. l%e contamination densittes b the delineated arm were related to the percentage of the total yield thatproduced ftssion products. Gamma-isodose plots were prepared from data obtained during Shots Zuni, Flathea~ Navajo, and Twit. N& fsi~~yt~qid be located following -t Cherokee and only on ltoll tslan&_titer, Shot Mohawk. determined because of contamination of project aircraft on D + 1 day by airborne radioactive material that resulted-in a high background. However, extrapolated values tndkate 29 percent of its fission-product yieM”~ present as fallout in the local area. The fallout from the wter - surface shots ~ concentrated primarily in tbe more remote areas, and l relatively small amount fetl close to ground zero. Helicopters and P2V- strcraft were used to gather data for atr-absorption measurements. The aerial-survey technique may be used directly for radtologicd surveys over land. Over the sea, the depth of mtxing of the fallout in the water volume must be determined before the sumey results may be converted to equivalent land-fallout contours and contamlnation4ensity “ distributions. Data on depth d mtxing was obtained from samples of sea water collected by the Us. Naval Radiological Defense Laboratory and the Scripps 2natMute of Oceanography. Repeated lertal surveys provided information on the stability d the contaminated volum~. .

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Patrol 4uadrcMI ONE, U.S. Navy, operated the aLrcraft used for the serial eurveys. The suthox gratefuU$ lcknowledges the diligence and high professional tompe~ which contributed so His efforts were resp>ndble for the fulfillment of the project’s atrctit reuutiemen~. Members of the Health and Safety bboramry, U.S. Atodc Eoergy Cornm@sio% who pe.rticthe Instruments Branch and IL 0’Brien of the Radiation B-A

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Prior to the o~ration, lerial surveys were scheduled to follow @ote Cherokee, ZunL, Flatbead, Navajo, Apache (secondary participation), and Tewa. Because Shot Cherokee was delaye& Program 2 requested that tie project add Shot Mcrosse to Us schedule ,ln order to give the lertal survey an opportunity to obtain operational experience. However, thts smfey m c~celle4 because flight clearance below. 1,000 feet tn the region of Eniwetok Atoll could not be obtained. - A change in the Apache scheduling introduced a conflict wttb the project’s parttctpation durtng Navajo. Tbe new schedule called for dual capability tnvolving both Enlwetok and Bikint Atolls. Participation tn Apache was therefore, canceled. Because of the long waiting period between P’latbead and Navajo, the project requ~ted sec - onduy partictpatton M Shot Mohawk. Preshot surveys were flown before the Navajo and Tewa shck, based ons Pmgmrn 2 reques~ to define the background status residtlng from the fl~w of contaminated lagoon water over the reef at Biktnt. s&&Oha~a~@fla@o:--~~i8*ioa for * latter m Bubsequentlpcanceled at the request @.tbg projec~ because of l shortage @ personnel. Durtng June and July, lt was aecessq to assign two technictana to Kwajeleia to service the lerial-survey c!@pmerkt; thei~ore, they were no longer available for on-site operations. The project operations ares umrmrized to Tkble 2.1. dose Plots of the-contaminated ar&>@aL&ur~. The operations were primarily to secure lerial survey data; subsidiary measuremen~ were performed to support of tbts objecttve to correZate this data. Altitude lbsorptbn studies were rquired to vertfy the correction factors awd ta retating the aerta! susvey to 8 reference plane S feet above the stiace. Program 2 Control Center on the USS Estes, AGC-12, during the aertal-survey fltghts. me Air ~rationa Officer, Task Group 7.S, assumed prhrmry radio @ during thla period. The ptan of the project 8ir control tn the Program 2 Control Center ts shown tn Fiire 2.1. . me communication routtng ts shown tnPigure 2.2. The telemeter opl-tor logged all tncomtng ttoid informaUon w received from the radio operator on Channel C (6693 kc). Tbe Project 2.64 Operations ~~cer correlated the nkvigattonal and radiation data On me rough fligttt%ontrd. eharL Tbe plotter transferred this information to the tactical tsodose plo~ under the 8upCf11- “ sion of the 2.64 Project Wicer, who used the flight and isodose charts to determine the ne%t - area of se-h for each aircraft. The operations off~ccr bid out the requkd navigstio~l ti-

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lrences for the designated fltght legs lnd transferred thts information to Che working fllght log. ttoa wa$ H~Y~ m tie appropriate aircraft by the radio operator. D-day fltghta used one aircraft, with l second aircraft on standby. The flights were limited to the upwind areas until active fallout hkd ceased. &rface ship reports, received by the Proj - l Pmebot surveys ef lagoon water outside tk 8tkinl Atoll. lct 2.63 remeseatatives tn tbe Control Center, indicated when fallout bad stopped tn the close-tn downwind ~ector. The, aircraft WLSthen doat&lled through the area to limits descrbed by the ship report& The D-day flights delineated the upwtnd boundary and obtained some tnteasity readings la tbe radioactive area trnmediately downwtad d grmad zero. * aircraft were used on D + 1. One delineated the close-tn radioactive area and coaftrmed the, upwind boundary located on the previous day. The second aircraft flew an”extensive search . pattern to locate the edges of the contaminated -. cleat. However; tbe Tewa pattern waa ~o large that two atrcraft were Deeded. Flights oa subsequent days used one alrctit and tracked tbe area until the dose rates became too low for were plotted ta the control center to gu!de tbe Project 2.62 surface ships wtth U@r oceanograpltic During the period prior to the oext shot, each aircraft was s&eduled to spend l day on Site Fred for instrument calibration and service. Two technlciahs calibrated each radtatioa detector tectors to Site Elmer between shots, where a complete routine battery change sod recalibration

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2.2.2 Altitude Absorption. Because considerations of fUght safety limit the minimum altitude lt which airctit csn fly over water, lutomattc gamma monitors were mounted over the sides of two lhips of Project 2.10, to measure the gamme-radiation field at S5 feet l~ve the sea surface. 7bI$ was to provide low-altitude readings simultaneous wtth lircraft passes b the same area Survey airc~t made lltltude-calibration passes over Wands of the Enlwtok Atoll after Shot Mohawk. After Shot Tewa, the P2V-S dropped l smoke light in the open sea to be used as a “’ Sig$tion$l reference and made altitude passes in the vtctnity. These da~ ue examined for the rartation of mdiation reading between different flight altitudes and gtvea la Section S.2. eorrectkm-calibration data coUected by the survey aircraft. Because the helicopters could oot safely hover at low altitudes, complete information could mot be obtained. 2! @d been pbmd to obtain gamma -eaergy spectra d various aLtitudes above l contaminated surface., The 7bp Bat dose -rate response was to be compared to the gamma-energy specba to determine whether the assumption of atr-equipment response was vatid. However, tnstruroentation difficulties and the limitations in hovering altitudes resulted tn fragmentary data. The survey using s sctn=eter obWned ~se-rate readings at altitudes between 25 and 1,000 feet. The major Instrumentation consisted of aerial radiation detectors. scintillation survey meters and shtp-mounted gamma monitors were used for measurements relating to aUKude-correction facto-. A spectrometer was used to obtatn the distribution of the gamma energies at survey altitudes. fie instruments are described tn Appendtx B. 2.S.1 Aertal Survey. Each of the project alrc nft had the foUowing equtpment: (1) Tbp Hat permanent components were Iaatalled by the Overhaul and Repair Ikp?~men\ U.S. Naval Alr f$tatIoq Ataine&, Caltfornta, l the air station prtor to @eration Redwtng. The removable components were installed by project persomel after the squadron deployed b the EPG. The location of the assemblies te idtcated to Figure 2.3. Tbe radiation detector was mounted aft to avoid the major areas of ltrcraft contamination, namely, the engines, oil-cooler atr intakes, leading ldges of the wings, propellers, lnd front of the radome. =e cabb intake ?eat$ were sealed to prevent contamination of the tntartor ductwork. Ttre control assembly and the operator were placed forn~ next to the navtgator. Thts facilitated close correlation bet~en the navigational and radiation repxta. The remainder of the e@prnent was located on am Tbe relatkmehtp of the various sections, both in the atrcraft and in the Program 2 ~tkl Center, te shcp in Figure 2.4. The radiation detector and Its associated control assembly drives a strip-ct& recorder to provide a permanen~ continuous reco.ti of the radiation Iotens!ties as measured in the alrcreft. Thts detector la aearty atr-equivalent from 80 to 1,400 kev, Figure 2.5. An annular radiation shjeld is built tnto the detector to reduce the effect of aircraft contamination. The angular response due to thte shield ts showo te Figure 2.6. The aircraft’s radio aItimeter (U.S. Navy APN-1) supplies an altitude indication to the altitude Compensator, which modifies the radiation detector so that its output ts l curreat that Is proporUonal @ the diaLion ~ch would M measured at S feet bve the surface. As the altttude changes, the compensator corrects the resulthg radiation change and keep Me g~-~vel ‘Ibe telemetering system dtd not pexform satisfactorily. The radiation readings on tie

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%3.2 Altlt ude Absorption. The lutomatic gamma monitors, HASL TN-4-C, we~e mounted on tbe YAG-39 and YAG-40. Each instrument was mounted at the lnd of a boom that was llso used to suspend the depth probe of Project 2.62. me boom lxtended 35 feet from the side of the ship and me set at en approximate mean height of 35 feet above the sea. An Esterline-AWW strtp-chu’l recorder was tnstalled in the sbtelded control room on tbe ship, to continuously record the gamma dose rste. The tnstallatlon of tbe monitors *nd recorders was accomplish~ Scintameter survey meters, IMSL T13-S-B and TE-7-A, were used for belloopter operatloea. Gamma dose rate was measured at various aItltudes over contaminated water and land sutiaceo.. . .. CAUS ASSSMBLT Al I Iieight analyzer, and a recorder, was loaded into the same heUcopter. The 28-volt power tn tbe helicopter was converted to 11S volt8, 60 cps, by a separate hfetier to supply tie swc~meter=. The count rate et various energy levels was obsemwd on a meter as tbe base line lutomattally swept through an energy scma from SOkm to 3 Mer. The survey alrcmft had tbe same instrument$Uon as described in the previous sectlox plus a Scintamettr sumey meter, TH-3-B.

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As discussed in Section 3.1.2, the distribution of gsmma encrgles m lstimated from the visual observations of l meter on the gamma spectrometer. Observations lt S00 and 800 feet above Site Sally on Mohawk D + 2 showed a general response where the predomi~nt portion of the lnergy spectrum fell between MO lnd 600 kev. dose nte at 3 feet above the lwface. The decay correction ts based on t -t.t. me flight altitude wss S00 feet for all surveys, so the lttitude correction ts based on I factOr d 23. . Figure 8.5 Flightgqttem Shot Cherokee D-day. ; The EOB is based on l mtntmum detectable LCmitby the detector d 0.01 rnr/hr. This con-. ~eti ~ 0.025 mr/hr at the surface. Where there lre 00 flight legs &s position to close an taodose pl~ dotted lines tndicate the estimated poattion. 7be estimates are -ed on prevtoua days’ results wherever possible. Contamination enclosed wlthtn an kdose boundedaru te calculated on the basts of the average gamma tntenelty between consecutive Iaodose lines, and a flight wms used for tnstrumat cbe~ because 00 contamination was found on the prCviOUS thy. 3.6). Because there was not lnough data to develop teodose pbt.a, radiation profiles have Mea plotted along the flight legs. ..

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~-hated patch -s suspected to be oortheast of Biktnl, baetd on the control center plots. ~ring the data reductlo% a navigational reporting l rror was discovered whtch changed the relatively uo~ted patch from the northeast to a position atmost due last of BtktnL further ~hmtion was scheduled k that sector. Ieodose Aree DlffereaceArea Averqe Cmtamtmtton ~.S.’S $hot Plathead. The D-da~ flight discovered relatively high dose k just west of Btktni (Figure 3.10). me pos!tioa immediately ldjacent to the reef tndicated that thte could be ‘A lagooointer passtng over the reef, mther than fallout. T’hk area w m comp~ete~y M~~#

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ss the I) + 1 survey does mot Indicate comparable dose rates. Tbe aircraft lncountered active fa!lout and becamt conbbtd. A replacement aircraft was flown to the survey lrea. This ok became contaminated. At no time waa the level tn tbe aircraft stlowed to exceed 20 mr/hr. Both aircraft on tbe D + $ fltghta (Hgure 3.11) were dao Mghtly contamltiti. Active fallout waa lncountered 100 miles northwest of Blktnl at E + 20 hours. Tbe -rtbwest sector was c1064 as far as aertd sumeys on D + 1 were concerned. u lndicatwf on tbe char& U wae sot possible to close the laodoae plot at that ttme. approximately 0.1 mr/br inside the detector shielding. The survey for this day could not detect any surface contamination readhg above a mintinum detectable ltmit of 0.25 rnr/hr at S feet from tbe surface. Table 3.4 summartses tbe fallout distribution. l Based en lstimated position of isodose he. . . Tbe EOB is roughly esttnmted and may not be representative of the lctual extent of the con3.S.4 Ebot Mohawk. A surrey of tbe Wands of Ediwetok Atoll was flown on D+ 1. Tbe island readings are shown b Plgure 3.12. The readings are referred to 3 feet lbove the surface of tbe telands by a factor of s.8 for the W&foot flight lltitude (Pigure 1.2). Sites Fred and Elmer were excluded from the survey patte~ because a W&foot ftigbt altitude would have interfered wttb &e air traffic to the wtctntty. .The open-sea aerLaI survey could find no detectable contamtnatton stties, repo@ed by project 2.62, ldjacent to the reef after 6bot Platbead, could have come from @ a D- 1 survey, was d completed because of malfunction. Z%ebackground surveys were coordinated with l Project 2.62 sblp survey. Becauee the lkpe and position of tbe contaminated area varied from day to day, U ta posstble that the vartatton may ~ve ken l function of the surface wtnde. An outline of tbe area, b$$ti on tie lhlP till b$d disappeare& Reef readings have been tncluded tn this chart.

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!. shot, ~tbed, much of the fallout remains lirborne. Tbua, fatlout lnd mixing In the sea could be expected to persist well MOD+ 1. TABLE S.S SUNMARY OF FALMUT DISTRIBUTION, NAVAJO l 3aaed aI lstimate ef Iaodoee posttiai. D +1 surrey (Figure S.22) discovered l contaminated area exteoding over 200 miles west of BSkinL The outside boundary could not be closed on thts survey, becwse of the far-out sector contained actSve falloutfrom Shot Huron. ma D+ 2 survey (FiguIw 3.23) extended the estimated poslttoa of the EOB. Tbe tsodose vae still oot completely c~ed. The lircraft was not allowed to Iose radio contact, so the survey …