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Defense Documentation Center Defense Logistics Agency

Cameron Station l Alexandria, Virginia

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(1) U. S. Saval IladMoglcal Defense Iaboratory fI.part lEKWi-=-l39 ent,itLd “1 Pallout Forecasting Technique with R%wlts thtained at the’ bimtok Pravi.ng Ground.

1. A n&hod fo; fomcs&irg fallout areaa “as deueloopd to supply tha opxxtlcxxl needs of scisntiflc projecta at +.hs Rr,iwt.ok Pmving Grounds. Th:, method amploy~ .a sbplifiad clouh n&e1 and distribution of particles in tb cloud based on p&meters Ibt;lized frou’previcus aeapons tests

‘. ‘. and Iron tlxory. ‘&%a prticlas ala t&ked to the l arth’s surface by

. . considatig tmir. fal_li&il: spee& and a::ecta of the ri+ds azIstlng al&t. Track+ is siz?pl&fied by use of the plbtting device dwcribed in a ‘_ previous report.

2. The end product of this technique ti a plot sbming the prlx;ster of the fallout area, the “hot line”, OT I&IO through the cmtor of areas of hi&est r&dlation Intensity, and tlx tibs of.&rrival of fallout I.&o&- out the ama.. The qsthad dbns not yield the lntrnsity of radhtion in tb a?*a. %olonever, relative intewitler :w be surzlssd usun,ir,g a radiation gridier.t from the hot .lina to tba pcrinater.

.3. Pallout forecasts mada dth thin tschniqua for four r’ rts at a rseent opratlon are cb;lpamd,n+th areas of nsapured failout. The coe~ison is excel.lant and it is evident that the tszbni&o nor&u ao mll for water

: surface as for land surface detonations.

I,. %is tethod &Y s+ls, f:ot, -I+ sul.tabl. for field us.. It ea,,, theafor*, be adapted to the nmda of militzwy forces in the li*ld.

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UNCLASSIFIED e------___--

.

A FALLOUT FORECASTING TECHNK?UL WITH R-ZSULTS OBTNlr’ED AT THE EMWETOK PROV1N.G GROUND

R$sc+rch md Derclopmcnt Technical Rcpoit USNRDL-TR-139

NS 081-001 U.S. Arm7

3 April 1957

E. A. Sehucrt

Physics Technical Objective AW-7

Radiological Capabilities Sranch T. Triffet. Head

Scientific Director P. C. Tompkins

Chemical Technology Division

E. R. Tompkins. Head

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Commanding Officer and Director Captain Richard 5. Mandrlkorn,USN

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U.S. NAVAL RADICLOGICAL DEFENSE LABORATORY San Francisco 24. California

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ABSTRiLCT SUMMARY

. A gencra@sed fallou: forecasting tecl’aiqne is presented

with deteilcd cotiputoti’ms of input parameters which weI= used at the Eniwetok Proving C::ound.

Results obtained at a recent weapons tert’are briefly discussed by comparison of forecast fallout with prelimiury measured &la.

The Problem

A fiOlOUt forecasting technique is needed to qualitatively .dercribc the fallout Baird resulting from nuclear decoy_ tions. This tcctwique should hare such flexibility that its em~loyrr.c~Z is valid for field use.

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A summary of ttx latest experimental and theoretical con_ siderations +s resu!ted in the dercloprr.cnt of a iectnique whose complexity is de;undrnt on rbe required accuracy of the results desired. tested at the

Such a techniqr;c has been satisfactorily Eniwetok Prdving Grounds for land surface ad

water surface bursts.

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; Fig. 1 Mushroom Diameter as L Function of Yield _ _ . _ . . if Table 1

2 ‘I Mus)itoom Height as a Function of Yield _ _ _ _ . . . 19

3;: ;.5+cc Model . . . . . . . . . . . . . . . . . . . . . 21 2 4 i Tsmnerature as a Function of Altitude for a L(1_rsball .

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Sxlu;ds Atmosphere . . . . . . . . . . . _ _ _ _ _ . . 23’ J

4 Pressur+ a& a Function of Altitude for a ?&r&&l Man45 Atmosphere . . . : . . . . . . . . _ . i . .

Density as a Function of Altitude Ior a bIarsb& Islands Atmosplwrc . . . . . . . . . . . _ . . . . .

Absolute Viscosity as a Function of Altitude for a MarrhaU Islrudr Atmosphere . . . . . . . - . . . .

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Falling Speed Transition G&s Ioi’the A.f.arsi+;l Islands as a Function of Particle Sire and titk&z . .

Basic Fall& Plot &wing Grid of Size Liars aad Height Lines i...............-...

Comparison of Plotting ‘fechniques Either by Ce of Trajectories or by Use of a Size Line _ _ _ _ _ _ _ _

Fallout Plotting Device . . . . _ . . . . _ _ _ _ . .

Comparison of Fallout Forecast with Test Resuks - ShorA . . . . . . . . . . . . . . . . . .._e...

Comparison of Fallout Forecast with Test Rcsr;T=r - ShotB . . . . . . . . . . . . . . . . . . ---...

Comparison of Fallout Forecast with Test Rcr& -

sllorc . . . . . . . . . . . . . . . . . ..;.--. Comparison of Fallout Forecast with Test Rcruks - Shotb . . . . . . . . . . . . . . . . . . . .__...

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TARLES

Temperzt~rr, Pre+sr;rc. Density. and Viscosity of the Atmosphere Over the Marsh11 IsLnrls

During th Spring . . . . . . . _ . . . . . . . . . . 4a

Falling Speeds as a Fun&on of Altitude . . . . . - . 48

Cumulative Time of Fall for 75-g Rrticlcs . . . - - 49

Cunwlative Time of Fall for 100-p Particlcs . . . . . 51

Cumulative Time of *all for ZOO-JZ Particles . . . . . 53

Cwx!ative Time of Fail for 350-a Particles _ _ . . . 55

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1 1NfRODUCTlON

Fallout research continues to seek a theoretical .r&ki.xg modes tba: till describe m detai; tbt mecbatirm~of fallout. Acide Srom- tkis long-range pyoblcm.. co$derrtion mcst be pi&n to making available a working tool that will meet the zeeds of the military for solviag fall- out droblems in tbe field. Such considerrtioe requires a simplified rapid system capable of Freduiing q.alitative 3 not quantitative :t$z$z.

Within a program studying fa.llout at + recent weapons test opera_ tion there was a f.+llout forecrsting assignment tbt had many a.s~c~s of the practical field problem yet, at the s;me time, required. h&titative results for use in reducing other *ata. This propram needed nositicaina data such that three ships-cotid he located prbpe;ly in the ‘f.&ut to obt&, data on its parameters. Also. aerial ;ml octanograpbii survey projects required knowledge of the fallout to instigate their naigrtional procedurea properly.

To meet these requircm&ts a tccbnique for rapid fallout forecrst- ing was dcvelopcd wbicb net only satisfied the needs of the fallout program but also was accurate enough to allow comp+riron between the mcteoro- logical aspects of model work and the results obtained from surface measurements. This technique was restricted tc dcscribizg quantitatively the perimeter of the fallout. the axis of the “hot line.” and to determining the time of arrival cf fallout throughout the pattern. No attempt was made to quantitate the expected lpvels of gamma rciivity OS to devtJop radiation contour lines.

At this operation. the Task Force employed a fallout prediction unit for determining the safe time to detonate ttie test devices. Altbouah many of their t&bniques for forec’asting were similar to those described in this report. their problem was of a different nature than that of the fallout prbgr&n. S&er+i of tbeir methods were unique ia that portable analog computers were tested as field instruments. T&se computers permitted corlsidtration of many complex parameters. One, in pr:ic- alar. obtained essentially-an inrtantaneorrs solution to tke problem oace the meteorological data weri available. .

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The falio~ program and the Task Force prediction unit functioned independently. !t ‘=a~ not fcrsibie inr the two :o employ the same tech_ niqoe beciuse the post shot variability of the winds aloft were es-~ckllv . ~ crkcal in ship lo.cat:on probiems of the fallout program. This problem will be discussed in detail later.

1.1 Objective

This report describer l technique for forecasting fallout employed at a recent weapons test operation. The results obtained in the field arc discussed as rumples of the reliability qf th techniques. Although tbe technique was deiigned for analysts of kind surface detonat+mm where the fallout is &aWcSte. itr app-1 “&tion to riiter surface detaoatians * consid+rcd.

2 FORECASTIHG TECHSIOUE

The forcca*ting technique .us)cs mrcy ideas from fallout model work. Several simpli5icatiora. as well as a plowing device. h;ve been developed to the end that the time involved bus been reduced vreatlv without sacri- ficing accuracy. In general, an initial source of a&vity’is defined,. describing the “stabiliad” nuclear cloud by appropriate spatial and size distributions of radioactive rurticlcs. These particles are tracked to rb; earth’s rurface by cons&ring their fifing speeds and effects of the winds existing &oft.

2.1 Bar& Co-siderations .-

In some cases ibc input parameters for the forecasting technique were obtained from;_er pans test measurements. lo others, where data were lacking, the parameters were derived from theory.

.?.I.1 Source Model

The optica! or visible dimensions of the initial cloud from a nuc!ear detonation have been documented in past weapons tests. Avail- able <ata describe strcb parameters 4s keight to base of mushroom. height to top of mushroom. and mushrootihiame:er as functions of time. Vertical rise stab::;zes in approximately 6 min.post detonation. This time is independent of yield.&ever. tie erp&ion of the musbroom diane:er. particu!arly for the megatcri devices. continues for perhaps

30 min. Avriiable diameter measurernenfs tiae not been made in excess

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of H+IO min. borever f%rIy reliable data are. known for the op+al F;aod dimensions as functions of yield to H+lO ~MI. Tte ultiuafz cloud diameter can br esirapokted from Ior yield Corvus and some qaalita- tire data. Figures 1 sod L present values of ‘A= cIoud dirzcpsicru from pas* tests. The ,OUICC m&e& ‘III. r~owrd cylindrici; bavmg. for a given yield. these dimcnritms. lu stem diameter was taken as 10 per- cent of mclrhroom diameter.

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2.1.2 Activity Dietribotion ia Source Yodel

Th grcrtcr part.of the activity vas rrquwd to be coocenrrrted in the lmrer third of the mushroom. The lower two-&rds of the stem was ignored; the remainder of the stem aad zapper t&o-tlrrds oi the clood were weighted lightly. This description (Fig. 3) oft& activity diirtribo- tia within the cloud ap:-ecared most reasonable io the ‘i&t of rrtible $ata and logical th~or&+ considerations. The rcc.& RC EOLICCP- t&ted nearer the axis of symmetry of rh cloud thn at IU outer edges.

2.1.3 Particle Size Distribuion in, Scurce Model

AU particle sizes were assumed at all clevatioos vi&it. the clood except the lower two-thirds of tte stem. Hove\-cr. to obrrrn agreement with past falloat =neas~reaetis and rrtb rtr o?t:ca) dkmcter of the mushroom. it was necessary to fractiorata the particle sirr distribution radially within the cload. cltte,raise lb.2 qorr?c:ei fallow area about gromd zero =uuld’be too large. The fractmzatma was specified as follows: particles of 1000 aicrons ia dkmcter and larger were restricted to,tbe ih’rcr 10 Frcent of the m~shroo:o radius or approximately the stem r&iur; those from St0 to it255 microns in diameter were limited to th ixzer 50 percect of :be cloud radios. Since the relation of activi.ty to particle size is so.rx &xctiaac:ionott& particle diameter.* this fractionation tends to c~ltentr~tit the activity about th axis of synrmctry of the cloud.

2.1.4 Particle Falling Speeds or Settling Rates

Computitioos of the terminal vc:aities of tte prtic!cs vcrc based on aerod)rzunic consideraticas for a stilJ atmos~herc havtig

. . temperature and dcnsrty distri.bctiaPs rtmorpberc in :be spring months.

:)~lcal of tbe Marstau Is_

Egrimenu) data from past tests at L=xructok Atoll i&icated that the particles were irreg*&r IP sbpe xnd bad a mean density of 2.36 g/c* cm.

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It tin be ‘hewn that particle’ falling at ttcar terminal ‘xed experience thrcr type, of flow in a tluld: ‘tresmlwc or kminirAsa where vi’coc’ force’ predominate (IO-’ .4 R, A 2.61: :ntcrmedu:c Z&v where inertia force’ prc+minate (2 4 R, s 500): ad turbulent Ear where iwrtia forces prcdor+xate (500 6 R, r5 III’)_ number of IO-’

Below a Reynolds

certain correction’ mua be applied i2 the equua’ because the particle diameter apxtycbes the-kern iree path of -A fluid medium: :he region above L Reynolds number of IS’ 5’ imnortanc onlv

in ballistic’. These 1imitir.g case’ will not be disc-red l&e. ’

The parameter’ actively affecting a partictr” falling s-d are: it’ i;;ght: it’ drag coefficjcnt; it’ density; as well a’ th t& density and fluid viscosity.

Most empirical equations de&loped in pa’: cxperimeti work have been for spbercs diopped in various liquids. Eme work bu ticen done on irregular-&aped particle’ +nd some done ia wind tunneir, Th

equations’ used to dethrmine thz faihg rates for _zs&xiclis~in a Cad medium follow.

For streamline motion. l.G-’ 4 Rs 4 2.0

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where

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terminal vcloci:y in cm/ret

particle density in gm/cm’

fluid density in gm/cm’

particle diameter in cm

absolute viscosity of fluid iti poises

ccn’tant incorporating gravity

54.5 for sphere’

36.0 far irregular-qhapcd pa’rticles.

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The data on pressure. temperature. density, rnd viscosity in I-OOG-ft intervals to 120,000 A sre summarized in Tablc~l.*

2.1.6 _ Terminal Velocity Computations

The average fatting spredzgh SOOC-It layers wss compted for four particle sines over sn altitude range from 0 to 120.000 ft. In these computations all in-flight trsnsition of the particles from strewn- line to intermedidte flow had to be considered through use of the p!-‘_ shown in F:g. 8.

Four &rtisle sires (75. 100. ZOO. and 350 )I diameter) were employed since &here wss evidence fram past tests that the 75-p particle defined the litii@tg d’$tsnce of fniiout of interest and the larger sines

r best described’$l&‘~.tt,rn within this limit. Table 2 presents the falling speeds computed for the four sizes. Tables 3, 2, 5. and 6 dispky the cumulative time 6f kll from s given altitude for these particle diameters.

2.1.7 Mettorologicrl Procedures

It is nccessar$ to have available the best .possible description of the winds a?dt in order to determine the arrival points of particles of various sizes originating at various altitudes. Such data nre irsually avail- abel from the normal upper air soundings routinely taken by Weather Cure+u and Military Meteorological stations. Although wind velocity ss P function of height varies continuously speed and direction in discrete Iryerr.

it cm be described by sn average Such averaging csn best bc

obtaincd.from the WBAN-20 Form where the original data sre recorded. The technique employed in this report wns to divide thz atmosphcr- into layers 5000 4 thick and determine sn sverage speed and direction for each layer. When ,the average falling speed of particles through these SOOO-ft :ayers and the speed and direction of the wind sre known, bori- zontal displacement csn be computed. Thus; for each particle size P vector may be drawn r-r t’.e svernge particle displaccm~nt in s psrticutrr 5000-ft layer. A*;ttion of such vectors from all layers d-scribed rbe tr.ajectary yrojeztion of s particle of given size. Simil+r plotting for ai3 particle sizes originsting at rll elevations within the cloud source wilr rnr.p the fsllout on the earth’s surface.

This technique is valid for rny atmosphere that has negligible vertical motion and is in a steady state connition with respect to the horizontal winds during the time needed for the. slowest psrticle to fall from the hig.hrst altitude to the ground. Such on assumption is not realistic for situationssrising from many of the megaton devixs be- cause 15 to 20 hr sre necessary to establish the frllout urea. Conse- quently. when computrng particle trajecioriis. in attempt should be

-___ ______‘__.-. A-.-_ l A great da* of exc~llenf uppet ad &:* for rk L(l&i;.Lit -73 ob:~rned *I Oprrarion psawc*5

in IS%. ~eduuon of tkw dau nil rcwl: 1(1 a mrch kucr dcvnp& oi ir iil&.~~ Mae& .,mmphere *ha. ha, &Gl prriovl1: l rait&te.

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made to consider how the wind varies with time and bow it varies with distance from. gra!nd zero; w!ut effect vertical motions bsve on particle falling speeds and how they vary with space and time. Such considera- - _ tions com$icate computation 0iirajectLries extremely. In rno~t ca*es vrliti input dits describing these variables are not avsikble. This p&se

of the problem is discussed below. .

2.2 Plotting Technique

The use of “psrticle..sir.&’ and “t4gtf” &es in mappink fallout is s standsrd technique l rnp1oyed by most sralyticrl methods. Tbrs tech; nique rimply descrtbes n grid (Fig. 9) on the earth’s swkce hdicatiag viiere fallout partic:es of ce r*ain size: ti:‘!t arrive and from wk3.t l lrrtude

they c+ne. Thse f~tsrneters sre the basic dsta for describing the fall- out pitern.

Assumhg t:col?y sLrr2 ~~e.cisr+!~~-- AS cc.zii:ie.ar SiiitOut vcrricrl

motion or space vsriition of the winds, it is very eary to cocstrucr n . grid describlnp r.zirrI points 00 the earth’s surface for psrticles of various sites &iginating ht different altitudes. f&s grid is constructed by ignoring tLs horizontal distribution of psrtic?es in the cloud model and by’plotting those trsjectoriri that originste alcog the line s.‘urce’ describing the vertical a.nii of the cloud.

Plotting trajectories for erch particle size st every eurting elevl’_ trxr is the first step in determining tte resul&nt fallout Potter: however. ttr drafting involved is tedious and tirne_consurning. Tbir effort csn be reduced greatly bT plotting from the ground up, OS is done in t.he con- struction of L wird hodognph., Such a plot is’msde by stanka at ground zero and working up through the altitude increments to the desired elerr- tion. Aithough this technique d-s nrt p!ot the trajectory of the particle. it does define tbe arrival points LP the surface of the earth of psrticler starting st .e?ch altitude increment (Fig. 10). To ploc these size-lines one must mske the prrliininsry computstions of :jartic?e-frliing times through each rlcitude increment to obtain the displacement for various wind velor.ities as described earlier in the Sect&n on Terminal Velocity Computations (p 8).

A plotting device. (Fig. 11). &scribed elsewhere.’ x%cili:r&s the c.omputntionr required for the size-lines of the fallout pattern. Such devices were ‘constructed for four partacie sizer: 75. 1GO. ZGO. and 350 p in dismeter. With these plotters. tnjec,tories or size-lines can be pIerted from snr elevation up to IZO.GOO ft for the four particle sxr.es. The plotters autoaaticrlly sc--’ -rut for tkc variable particle Uiog

soecd. They also eliminate the need for draftins euuiotnenc. After es- _ . . ubl;sbing the psrtic!e arrival pox&s by either the USC of si--e-E-es or trsjectorics. height lines can be conrtrncted. These Ones. joining

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from Jurface zero. the ideal situation rculd be to take winds-aloft measurements throuahoui’the volume traversed by the particles. CQ.~- rection for space vr;iation of the winds is then necessary. however in most cases not as rl*nificant is is time variation. Most Weathrr net- works arc nnl refined enough $0 allow quantitative correction for there

- errors.,

2.2.3 Vcr:iczl Motiona

In appiying particle falling speeds to the forecasting technique. _ it is assumed that the atmosnherc has no vertical velocify. Compum. tions made it the Eniretok sroving Ground. to 50.000 it indicated that large cellular vertical motions. in <be atmosphere sometimes attained sneed: caual to and erester than the settling speed of a 75-p particle_ A time-space corre;ion should be madelo;& falling sjx=c& =f tba Farticier to compe?srte for this parameter. HoWever. in the work at

:Ce :e5: site it was not posribie to inciude this eifect in the flllout fore- Cast¶. Certain anomalies discussed below may be due to such an eifect and pogt shot analysis is being conducted to see whether they +re resolved when the vertical motions bavi been taken into account.

3 DISCUSSION OF FIELD TEST RESULTS

The forecastin techni~le described was employed by the fallout proycam at the Enivetok Proving Ground to satisfy certain project requitements. Ok project had three ships equipped to, collect fallout and their positions had to be determined for most efficient collection: another sampled the ocean for fallout: while another made an aerial survey of the contaminated area. The navigational schedules for these latter projects were based on the forecast fztllout pattern. Operations were controlled through the Program Czntrol Center aboard the Task

,Porce Command Ship where the forecasts were prepared. I.

. The meteorological data-were teceived from :ke weether ship at Bikini atoll as well as from weatherstations at Rangerik atoll and Eniweto*c

atoll. Furthcrmore.aU Corecasr.s made by t!x Ta& Force Weather Cen- . tral at Eniwetok atoll were usually available aboard the command ship

_ by facsimile through :he ships Weather Station.

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Upper air measuremente were rnadc at Rxkiti, RurgcriL.rndEnivctok atolls every 3 br starting at H-24 hr and continuing until H+Z4 br far any given Cctonation. Tbc frequency of obrcrvat~,.- wae ualully incrrc~sta

.during the period from H-6 10 H-L br. The rltilcdrr reached on ttc wind runs were remarkably high and gere prerhapc thr best set d vinds-aloft me~surcmcat~ to &tc. The +rerage tcrmxx:ion altitude was l oorox. ;mately ~O,SCB .‘I +tb ro&ny ruzs (iyer iGO.OiX ft. Such crcelle&. core erase of the viods alaft ns a major help in the fallout forcuctiag.

Fa!lo;lt forecast,% were made every 3 hr surting at H-24 hr.us&_a the mczsurrE rinds avaikble at ;ht time. This process was contin;lcd up to ‘shot time arid from then, on thq technique of corzcitiag for time x-aiiition. was employed every 3 hr until rtc frllo~t e ..er.t V~S cwplt ted. It was not feasible to cor:e:r for s*;ce v;.riitiun sti vertical m@ias d-ring :bis period because of the lack of time sod data.

3.1 Fallout Plots --

The fallout forecasts determined at the reapmr test ~:rz:ioo were based entirely on measured dita ard q;uc:i:ztive!v cmsidered rime variation of the wind, So space variation coriec:iozs or cox;xced values 01 vertical motions rCre emplo)-et in their cons.ructioa_

Ths area of measured frilout from shot A is corn-red with the &recast fallout plot in Fig. ir. Figcres 13. 14, *SC 15 ire sin-.lkr <ompar~sons for shots B. C. lad D. Aitbocgh C a=d i) were water surfa<c shots. 11 is evident that :he forecasting :ecL-iqGe saccecded in represem.ing the measured tallou: area as well is it did for :he land surface detonations, A and 8.

The comparison is rxceuent for rll shots rxce>t B and r.s >-;zt rte discrepancy between the forecast fa.113~: orea and t%r w&<h ars meas_ ured i; zzkzwrn. There ~5 xa-ce indication rtat conr~deratzon o! vertical motions sill have to be made for shot 3 dxing :he tinx of fall=: sarce computed vertical motions were slgcifx;mt in rnagti.tadc. Sccb rulysis including space variation is being carried omit at tk&s time for rll four detonations &d the refined data u-ill be pzblishcd :atcr_

4 SUMMARY

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a.t t”e Eniwetok Proving Ground. With known meteorological data such a technique will successfully quantify the area of fallout rrrd iudicate qualitatively the relative intensity of radiation.

Precise determination of the fallout area requires consideration of many complex’meteorological parameters. Kowever.from the above analy,sis a practical field tool csii be developed that in most cases will satisfactorily define the area of interest. .’

Approved by:

E.R. TOMP&NS H&30. Cheri.icrl Trchuurology Division

For the Scientific Director

i

!

REFERENCES

A

1. Dallavalle, I. M. Micromrritics. Pittman Pt;blishing Corporatioa. New Yoak. N. Y., .

2. Brunt. D. Physical :nd DynAmical Mcreorolc.gy. Cambridge University PresX&iXn.TZ--

3.

4. Smithsonian Physical Tat les. 1954.

Schuerr. E.A. A Fa:lout Plotling Device. U.S. Sara1 Radiological Defense Lbbcratory Technical Report USNRDL-127. February 1957.

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