Operation Redwing - Project 1.8, Crater Measurements (Deleted)

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Pacific Proving Grounds remains classifiedSECRET/FORMERLY RESTRICTED DATA as of thisdate. BEST COPY AVAIMBLE DEFENSE NUCLEAR AGENCY Approved for public release;

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1. REPORT MLJMCCR z GOVT ACCESSION NC Operation REDWING - Project 1.8 Headquarters Field Command Armed Forces Special Weapons Project Sandia Base, Albuquerque, N.M. It.CONTROLLINGOFFICE NAME ANO AOORESS Approved for public release; unlimited distribution. BEFORE COMPLETING FORM S. TYPE OF REPORT l pERIOD COVEREO 6. PERFORMING ORG. REPORT NUU8C~ AREA h WORK UNIT NUMS7iRS IB. SUPPLEMENTARY MOTES This report has had the classified information removed and has been republished in unclassified form for public release. This work was performed by the General Elect Company-TEllPOunder contract DNAOO1-79-C-0455 with the close cooperation of the Classification.Management Division of the Defense Nuclear Agency.

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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 reporthas been accomplished specifically to support the Department of Defense Nuclear Test Personnel Review (NTPR) Program. The objective is to facilitate studies of the 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 available copies of the original material. The locations from which material has been deleted is generally obvious by the spacings 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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This reportpresentsthepreliminary results of one of theprojects participating in the nli Iitary-effect programs of Operation Redwing. Overall information about this and the other n~iIitary-effect projects can be obtainedfrom WT– 1344, the “Summary Report of the C(l, omander. Task Unit 3.” This technical summary includes: (1)tables listing each detonation with its yield, type, environment, meteorological conditions, etc. ; (2) maps showing shot locations; (3) discussions of results by programs; (4) summaries of objectives, procedures, results, etc., for all projects; and (5) a listing of project reports for

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The objective of this project was to measure the physical characteristics of craters produced by the decoration of nuclear devices so as to obtain a more thorough understanding Crater measurements were made on the five surface or near-surface shots: Lacrosse, Zuni, Seminole, Mohawk, and Tewa. Crater radius, crater depth, and approximate profile were determined by use of aerial photography and lead-line sounding techniques. Aerial mapping photographs were made of the craters after the shots, and these were used to plot ground ele,rations to give the crater radius. Lead-line soundings were made along diameter(s) of each crater to determine the depth and average profile. The results are

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The authors gratefully acknowledge the assistance given by the chief and various members of the Special Projects Branch of the U. S. Army Engineer Research and Development Laboratories for their assistance throughout the planning and operational phases of the proassistance during all phases of the test; Lt. Colonel J. G. James and his staff for the the operational requirements for Holmes and Narver; Holmes and Narver personnel who made the preshot and postshot surveys; personnel of Project 5.6, including Floyd Gibbs and staff, IIastings-Raydist, Inc., for recording by Raydist the position of the boat while making the lead-line soundings for the Zuni crater; James W. Halbrook and Ivan R. Jarrett, Map Compilation Branch, U. S. Almy Engineer Research and Development Laboratories, for making photcgrammetric measurements from the aerial photographs; and Lt. Colonel out the program.

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4.1 Crater radius versus height of burst, scaled to 1 M-- --------------- 33

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The objective of this project was to measure the physical characteristics (radius, depth, and average profile) of craters produced by nuclear detonations. Data were gatherecl from Shots Lacr~, sse, Zuni, Seminole, Moha\vk, and Tewa. Although all were te ~med “surface” bursts, the burst elevations actually varied between a 300--foot tower to what may be considered a subsurface burst. It was a further objective of this project to correlate the data obtained with results from previous “surface” bursts at the Eniwetok Proving Ground Measurements of the apparent crater radius and depth for surface shots at the EPG had been made during Operations Greenhouse, Ivy, and Castle (References 1, 2, and 3), Aerial photography techniques were used in these instances to obtain dats on crater radius, and fathometer techniques were used during Castle to obtain depth measure rllents. Since these operations, no new techniques have been developed for the nlore-refined measurement of crater characteristics, even though more-accurate determination of the depth and profile of a water-filled crater is desirable. The aerial-mapping technique provides ample accuracy for the determination of the crater radius, since it provides data at early times after the burst, when the contamination from radioactive fallout is extremely high. Project personnel of the U. S. Army Engineer Research and Development Laboratories (USA ERDL), Fort Belvoir, Virginia, were successful in making early time measurements on the crater of Shot 7, Operation Teapot. Subsequent to that, Headquarters, Armed Forces Special Weapons Project (AFSWP), requested that USAERDL submit a project proposal for Operation Redwing to accomplish the previously outlinecl objectives. In an operation such as Redwing, where the land area available for detonation of largeyield surface bursts is small, compared with the predictable crater size, the extent of the measurements obtainable and an understanding of their physical significance and reliability need considerable clarification. The “apparent crater” is that which is visible to the eye subsequent to the completion of dynamic effects of the explosion, such as throwout and fallout. Such a definition is not readily ~plicable to the geologic condition encountered at EPG. If the sides of the crater break through to open water, considerable washing by wave action will alter the shape of the apparent crater as strictly defined. This effect would not be important, if it were desired only to compare these shots with others having

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the same general geologic conditions. This washing action would then take on a similar role to throwout or fallout in defining the phenomena. It would be highly desi lable to separate the water-actuated effects froln the direct blast-produced crater, but this capability is not yet a reality. Considering the operational difficulties of obtaining early-time crater measurements, a realistic approach would compare craters only when the ground or groundwater conditions are similar and include such i~duced phenomena as washing action into the definition of the apparent crater, since this induced effect is properly a part of the immediate recovery problem. The water-actuated effects are then a part of the weapon effects for these burst contiitions. However, these effects complicate the correlation, scaling, or complete understanding of crate ling phenomena from a technical point of view. Several other fa( tors affect the analysis of data obtained during this project and correlation with data obt:iined in the past. Ideally speaking, four variables determine the size of the crater from a near-surface detonation of ‘an eqlosive charge. The se are total blast yield, height above or depth below the air-earth interface, energy partition, and soil type. Knowing the relationships of these ~ariables, the volume of a crater and the ratio of its radius to its depth should be calclllable. For a nuclear surface l~urst, the portion of the hydrodynamic yield that manifests itself in cratering and ground shock can be evaluated on a TNT-equivalent basis by considering IVeight of TNT required to produce a given crater dimension Hydrodynamic yield to produce the same crater dimension. The use of the TNT equivalent aI1ows high-explosive cratering data to be converted into prediction curves for nuclear weapons. A drawback to this method is the fact that there is little high-exTlosive data for comparison, both from the point of view of soil type found at the EPG and the high yields necessary for direct comparison. Griggs (Reference 4) predicted for the Operation Jangle surface shot with good accuracy, calculating that onIy about 2 percent of the total energy release will go into the ground for a n’.iclear detonation on an air-ground planar interface. Other estimates by Porzel (Referwlce 1) indicate about O. 1 percent for EPG soil and 0.6 percent for the more porous Nevada Test Site (NTS) soil. The saturated soil at the EPG cannot be expected to absorb and transmit energy in the same manner as the NTS soil with its high air content (about 40 percent by volume). The NTS soil will react plastically, \vhereas the saturated soil at the EPG is considered essentially incompressible. nuclear explosions can be an extremely important weapon effect. TMre are certain target types, both surface and subsurface, that require a con’tict (i.e. , a crate ring) burst t(, cause significant damage. Massive concrete fortifications, underground structures, heavy industrial machinery, air fie Id runways, tunnels, and dams are good examples of this type of target. Probably just as important, tactically speaking, is the ability to achieve delaying action to an enemy by the use of craters, crater lips, and their high residual contamination as barriers. If a crater is to be used as an obstacle, or part of a barrier system, its effectik’eness is dependent upon the ratio of its radius to depth or the slope of its sides. Previous data indicate that for a surface burst as the yield increases so does this ratio, and as the depth

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stacle to vehicu!ar movement wh+n this ratio is small and the slope of the sides steep. It is felt that too much weight should not be placed on the nonconfori~~ity of individual craters forrr.ed from tower bursts, since these are depression craters formed in the hi~ii– overpressurc region of the burst. The outer limits of these craters are very hard to detect, except by very-accurate survey controls. This is particularly true when one realizes th~t the radius-to-depth ratio of the cl’ater being considered may be on the order of 100. In order for a military commander to properly use the cratering effect from a nuclear weapon and still execute tactical operations on the ground, he must have an understanding of the variation in crater dimensions due to the burst position of the weapon (above or below the air-earth interface), placement of the weapon (tamped or untarnped), yield of the We~pO(-lj and response of the media in the vicinity of the detonation.

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Aerial photogr:lphs were taken of each of the five shot areas (Lacrosse, Zuni, Seminole, Mohawk, and Tewa), so the apparent diameter of the crater could be measured photogrammetrically. Eipcsed crater contours were also determined by the same means. An RB50E aircraft equil,ped ivith a USAF aerial mapping camera, T-n, having a 6-inch focal length, \vas used to w ~e the n~apping runs. The camera was gyrostabilized and the intcrvaIo/neter was sot for a forward overlap of 57 to 62 percent. Calibration certificates are on file at USA ERDL for all T-II cameras, thus precluding the necessity for special calibration runs. Film was developed at EPG to insure proper coverage of the target and then sent to Fort Belvoir for anal~sis. Readings of a ladio altimeter, FCR 718, were taken at the beginning of each mapping run and any variations were noted. This instrument can indicate the altitude above the surface of the ground between 200 and 60,000 feet with an accuracy of + 25 feet over smooth terrain. The flight pattern was flowm as soon after the shot as possible (approximately Photog~amrnetric measurements were made at USAERDL. The accuracy of the stereoplotting equipment is limited by the deviation of the altimeter reading from the true value, since the error of the equipment is negligible by compari son. Lead-line soundings were taken to determine the depth of the apparent crater below the water surface. The time at which these soundings were taken was dependent upon the time required for the site radiation level to decay to a value such that the total exposure of the survey group would not amount to an important fraction of the total allowable dose for the entire operation, viz. , 3,900 mr. 2.2.1 Lacrosse. For early preliminary results, a sounding was taken from a helicopter positioned over apparent ground zero approximately 25 feet above the water surface. The sounding was later checked against those taken from a boat and found to be in agreement \\itllin 1 foot. Ii’hen residual radiation i{as low enough, a survey crew of shot survey and, using a skiff, made detailed soundings. Because of the symmetry indicated by postshot photography, it was determined that detailed soundings along one diameter would be sufficient, 2.2,2 Zuni. Because of the extensive breaching of the crater. the radiation level wras low enough to make rc-entry possible at survey crew of Holmes and h’arver went an ear Iier time than other shots. into the area and made soundings along the pre -

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ings \vere made was determined l-j’ Raydist. The use of Raydist to establisl. the horizontal control location of the lead-line sound-- ings had been previously planned to preclude the need for postsurvey personnel to land on Site Tare to accomplish the horizontal control by conventional survey trian=wlation methods. The Raydist equipment was already available, because of other Project 5.6 aircraft-tracing requirements. It was considered that the elimination of the need of survey personnel to land on Tare, with its expected relatively high postshot radiological contamination, would permit an earlier crater-depth survey by at least several days. Because of the rather severe postshot tidal-wash action expected through the Zuni crater area, which ~’ouId possibly modify the initial crater m::~surements considerably, it was obviously desirable that the postshot lead-line soundings be made as soon as possible after the shot. The position of ground zero was determined before shot time by Raydist, and the LChl craft was guided to this spot for the begin nirl~ of each run along the radii. The course of the craft along these radii was governed by compass direction. 2.2.3 Seminole, Mohawk, and Tewa. Residual radiation was too high for detailed soundings to be made of these craters while the operation was in progress. Soundings were taken from a helicopter at ground zero for Seminole and Mohawk and reported in the preliminary report. Lead- line soundings made by Holmes and Narver in September and October 1956 are reported in Chapter 3 of this report.

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The results of the crater surveys are summarized in Table 3.1. Figure 3.1 is s preshot phutogr~ph of the I.acrosse area. Figure 3.2 is a postshot photograph of the …