Preshock Sound Velocities Near the Ground in the Vicinity of an Atomic Explosion, Project 1.5, Operation Teapot

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BEST AVAILABLE COPY NEVADA TEST SITE PRESHOCK SOUND VELOCITIES NEAR THE GROITTD IN THE VICINITY OF AN ATOMIC EXPLOSION KAI LISTIC M1SS11.K DSVHJO in the Atomic £>ur?*^! Aci of 7964. Its tyansmittal or the disclosure erf zi% contents in cny manner to HEADOUASTERS FIELD COMMAND. ARMED fCTroTrT*cIOLTYfEAPONS PROJECT SANDIA BASE. A13U0DER0UE. NEW MEXICO

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BEST AVAILABLE COPY Inquiries relative to this report may be made to Chief, Armed Forces Special Weapons Project If this report is no longer needed, return to AEC Technical Information Service Extension Oak Ridge, Tennessee BEST AVAILABLE COPY

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BEST AVAILABLE COPY This document conslote of 76 pages, No145 of 210 copies. Series A Report to the Test Director PRESHOCK SOUND VELOCITIES NEAR THE GROUND IN THE VICINITY OF Navy Electronics Laboratory San Diego, California Ita transmittal pr the disclosure of lts<‘ contents In iny Aiannet tc'lin unauthorised person Is prohibited.

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BEST AVAILABLE COPY SUMMAHY OF SHOT DATA. OPERATION TEAPOT Shot Code Name Date Time* Area Type HI IT ii mi t Actual zero point 91 fret north. 62 feet west of T“7-4. 8 Actual zero point 36 feet aouth. 3'j7 feet woat of T-5. BEST AVAILABLE COPY

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BEST AVAILABLE COPY Preshock velocity of sound waves !n air were measured at elevations of iVi, 3, and 6 feet above grade level at 1,000- and 2,000-fool ranges during Shot 12 over desert soli, water, asphalt, concrete, fir boughs, and Ivy. Twenty-three of the original twenty-four channels recorded velocity from less than 20 msec after detonation to shock-wave arrival. The sound velocities at elevations from l/j to 6 feet above grade level were very similar and averaged around 9 percent above ambient in most cases. Velocities measured over asphalt, water, desert soil, and concrete were very similar In amplitude., Maximum velocities occurring just before shock arrival were similar at the 1,000-000-foot ranges. Air sound velocities were measured over fir boughs and Ivy ^Velocities measured above the fir boughs were the highest recorded, reaching 18 percent above ambient at the iVj-foot elevation. Ve locities over the Ivy plot were similar to those over the fir boughs; however, the medium over the ivy appeared to be more turbulent, and consequently some (Lata were unreadable. BEST AVAILABLE COPY

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BEST AVAILABLE COPY This report presents the final results of one of the 5G projects comprising the Military Effects Program of Operation Teapot, which Included 14 test detonations at the Nevada Test Site in 1955. For overall Teapot military-effects Information, the reader is referred to the which includes the following: (I) a description of each -detonaiJon including yield, zeropoint location and environment, type of device, ambient atmospheric conditions, etc.; (2) a discussion of project results; (3) a summary of the objectives and results of each project; (4) a listing of project reports for the Military Effects Program. McLellon, Director, Program 3; Lt Col J.J. Haley, Chief, Requirements Branch; and his assistant, LCDR A. P. Mlnwegen for the wholehearted cooperation they rendered to Project 1.5 at all times. Electronics Laboratory engineers for their capable work on the Project 1.5 Instrumentation. The author gratefully acknowledges the fine support given by all people who par ticipated in the project.

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BEST AVAILABLE COPY 2.1 Desert Sand, Asphalt, and Water; 1,000-Foot Ground Range -------------------11 2.2 Desert Sand, Asphalt, and Concrete; 2,000-Foot Ground Range---------------11 CHAPTER 3 INSTRUMENTATION AND REMARKS-------------------------------------------- 22 3.1 Basic Sound Velocity Meter---------------------------------------------------------------- 22 3.2 Changes in Instrumentation -------------------------------- 23 3.4 Transducers and the Air Path------------------------------------ 24 3.5 Attenuation of the Acoustic Signal In the Air Gap----------------------------------- 28 3.6 Other Measurements of Velocity----------------------------------------------------------31 3.7 Attenuation of Acoustic Signals Caused by Heating Various Parts of the Microphone----------------------------------------------------------32 4.1 Calculations of Preshock Sound Velocity from Peak-Pressure, 4.2.2 Data Comparisons with Previous Precursor Shots----------------------- 39 CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS ---------------------------------- 42

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APPENDIX D PHASE AND AMPLITUDE CHANGES DUE TO INTERFERENCE OF SOUNDWAVES.................................. **6 APPENDIX D CALCULATIONS OF ATTENUATION OF SOUND APPENDIX E ATTENUATION OF ACOUSTIC SIGNALS MEASURED APPENDIX F RECORDINGS OF RAW DATA MADE BY PROJECT 3.1 Results of Test of Project 1.5 Velocity Meter In Paint Oven 1.1 Blast Velocities and Corresponding Air Temperatures --- 1.1 Blast line layout showing positions of Project 1.5 (NEL) sound 2.1 Preshock air sound velocity versus time, 1,000-foot range, over desert, asphalt and water surfaces----------------------------------12 2.2 Preshock air sound velocity versus time, 1,000-foot range, 2.3 Preshock air sound velocity versus time, 1,000-foot range. 2.4 Preshock air sound velocity versus time, 1,000-foot range, 2.5 Preshock air sound velocity versus time, 2,000-foot range, over desert, asphalt and concrete surfaces------------- 16 2.6 Preshock air sound velocity versus time, 2,000-foot range, 2.7 Preshock air sound velocity versus time, 2,000-foot range, 2.3 Preshock ulr sound >eloclty versus time, 2,000-foot range, 2.9 Preshock air sound velocity versus time, 2,000-foot range, 2.10 Preshock air sound velocity versus time, 2,000-foot range, 3.1 Sound velocity meter transducers used en Upshot-Knothole------- ----------- 23 3.2 Directivity pattern of AUec-LansIng 802-C loudspeaker at frequency 3.2 kc with attached horn---------------------------------------- 26

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Effi'ct of directivity patterns on direct and Indirect signals ------------------- 27 Sound velocity meter three feet above flaming gasoline--------------------------29 Measured sound velocities and signal amplitudes three feet above flaming gasoline tins ---------------------------------------------------- 30 Effect of burning copper screen In horn throat on microphone-----------------33 Effect of applying a blowtorch flame to horn of microphone--------------------- 33 Signal amplitude versus time for condition where blowtorch la played over microphone horn------------------------------------------------ 34 Electronics for one typical field station, three channels------------------------ Recorded acoustic signal showing effects of electromagnetic Model of NKL Instrument shelter with dimensions of full-size Model of NEL Instrument shelter-------------------------------------------------------- 49 Details of NEL Instrument shelter model---------------------------------------------- ‘*3 Relative sound pressureamplitude versus time, 1, 000-footdesert----------- 52 Relative sound pressureamplitude versus time, 1, 000-foot asphalt--------52 Relative sound pressureamplitude versus time, 1, 000-footwater----------- 53 Relative sound pressure amplitude versus time, 2, 000-footdesert----------- 53 Relative sound pressureamplitude versus time, 2, 000-footasphalt-------- Relative sound pressure amplitude versus time, 2,000-foot concrete------- 54 Relative sound pressure amplitude versus time, 2, 900-footflr bough----- 55 Relative sound pressure amplitude versus time, 2, 000-footlvy------------- Channel 19; desert, 2, 000-foot ground range, iVj-foot elevation------------- 57 Channel 23; concrete, 2, 000-foot ground range, 3-foot elevation ------------ 55 Channel 16; white fir boughs, 2, 000-footground range, Channel 17; white fir boughs, 2, 000-footground range, Channel 18; white fir boughs, 2, 000-footground range, Channel 13; broad leaf cover (Ivy), 2, 000-footground range, BEST AVAILABLE COPY

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BEST AVAILABLE COPY F.23 Channel 15; broad leaf cover (Ivy), 2,000-foot ground range, BEST AVAILABLE COPY

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The primary objective was to determine preshock air sound velocities at elevations up to 6 feel above the ground In the region where the precursor wave existed. It was felt that this Information would be valuable in explaining the generation of the precursor. Shot 12 was a 2't-kt device detonated on a tower at 400-foot elevation and, consequently, fulfilled the conditions for a pieevrsor-gencrating shot (Itefcrcnce 4). Measurements of preshock air sound velocity were made over three different blast lims: (l) a regular Frenchman Flat desert blast line; (2) tin asphalt-covered blast line; tind (3) a water-covered blast line. Velocity meters were situated at the 1,000- and 2,000-foot ranges on the first two lines and only at the 1,000-foot range on the third Also, measurements of preshock tdr sound velocity were made over three special surface plots situated in the vicinity of the 2,000-foot station on the desert line. One plot was composed of concrete, a second of white fir boughs and a third of broad leaf cover or Ivy. The dimensions of all plots were 20 by 30 feet with the shorter dimension oriented along the blast line. On previous tests (References 1, 2, and 3) data were gathered on air sound veloc ities and air temperatures from I’/j to 51 feet above desert soil. .In general, there were level over Nevada soil. Below the 10-foot level, the velocities ami temperatures were known to be above ambient, but no gradient had been established. Also, only meager data of. this type had ever been taken in the zone of interest on previous precursorAsphalt is a convenient ground cover which tends to absorb most of the thermal ra diation incident upon it. It tends to emit smoke and also to impart its heat energy to the atr by conduction anil eonvcctlcm. Tbe preshock air sound velocities over ibis surface are of interest in explaining blast-wave performances over dust-free, thermal-absorbing Water Is probably the cheapest and mos* feasible highly reflecting surface available. II was expected that the air above the water surface would not change In temperature, since the surface Itself would not absorb thermal radiation and, hence, rould not trans fer Its heat to the air by conduction or convection.

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BEST AVAILABLE COPY In Upohot-Knothole Shot 9. *Ir sound velocities were measured over three different plots of white fir boughs. Plot dia'.enslons were 40 by 28 feet. Velocities measured were two to three times ambient. A similar plot of white fir boughs was set up at 2,000-foot range on the desert line, in Teapot Shot 12. Also, a plot of broad leaf cover or Ivy and a plot of ordinary concrete CD Meters over ccncrete slab. A Meters over ivy p’-ot. At oil stolions meters ore 1.5, 3, ond 6ft. from the surface. Figure 1.1 Blast lice layout showing positions of Project 1.5 (NEL) sound were situated at the same lo'*.’don. Dimensions of these plots were 30 by 20 feet. Thermal effects on these special surfaces are apt to be quite different from thoae occurring on the ordinary desert terrain. Consequently, for a relatively small cost, comparisons of preshock air sound velocities over different plots can be made. Thla In turn might indicate variations In blast-wave performance over the various surfaces. BEST AVAILABLE COPY

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The graphs of Figures 2.1 through 2.10 depict the recorded values of the velocity of sound In air from zero time (time of detonation) to the arrival of the shock wave for 23 of the original 24 channels. The iVj-foot elevation meter at the 1,000-foot range on the water line failed at detonation. The points that appear on the curves are the actual values taken directly from the raw data—no averaging of any sort has been done. Discrepancies between these curves and those In the preliminary Project 1.5 report lITR-1104), resulted, since for this report travel times across the air path have been read with the greater accuracy of the 3,200-cps carrier Instead of the 100-cps modulating signal. In order to roughly compare alr-sound-veloclty change with air-temperature change, the conversion 2 ft/s/’C may be used svlth the mental reservation that It applies strictly to clean air whose chemical composition does not change. 2.1 DESERT SAND. ASPHALT, AND WATER; Figure 2.1 depicts the change In the air sound velocity from detonation to shock arrival at elevations of I'/j , 3 and 6 feet above sand, asphalt, and water surfaces at a ground range of 1,000 feet. These curves Indicate a velocity Increase rate of approxi mately 1 ft/sec/msec Irrespective of elevation. The magnitude of the velocity change also seems to be Independent of the surface. The fact that the sound velocity over the water Is higher than over the other surfaces Is not considered significant. This veloc ity differential represents approximately 0.2 msec out of 5.0 msec total signal travel time from one diaphragm to the other, 6 feet away. It la possible that the greater re flectance of the water surface caused the microphone horns In the Instruments on the water line to receive more radiation than those on the other lines. A small hlghtemperature region close to the transducer horns could easily account for the Indicated change In transit time. The same curves shown In Figure 2.1 are plotted Individually In Figures 2.2 through 2.4; these Include the ohock-arrlval Instants In each case. 2.2 DESERT SAND, ASPHALT. AND CONCRETE; 2.000- FOOT GROUND RANGE In Figure 2.5 preshock air sound velocities over desert soil, asphalt, and concrete surfaces at 2,000-foot ground range arc plotted versus time. The first velocity In creases-occur about 70 msec after detonation at this range compared with 40 to 50 msec at the 1,000-foot ground range. After this the rate of Increase at the three elevations at 2,000-foot range Is approximately 0.8 ft/sec/msec. After 250 msec there is little velocity increase at any elevation or over any of the three surfaces. At neither the 1,000-foot nor the 2,000-foot range do the velocity magnitudes reach 1,300 ft/eec at any elevation or over any surface so far considered.

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In Figures 2.6 through 2.8 the same curves depicted in Figure 2.5 are presented along with the respective shock-arrival times. 2.3 Flit BOl’C.HS AND IVY Preshock .»«r sound velocities over a surface of white fir boughs and an Ivy surface are depicted for elevations of 1V2, 3, and 6 feet in Figures 2.9 and 2.10, respectively. Figure 2.1 Preshock air sound velocity versus time, 1000-foot range, over desert, asphalt and water surfaces. BEST AVAILABLE COPY

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Vo-A,' BEST AVAILABLE COPY Jutting from the distortion of the recorded signals (Appendix Fi. extreme turoulence existed over the Ivy plot, much more, in fact, than over any other surface. The velocitj recorded over the untile fir boughs at iVj-foot elevation was the highest recorded on any channel—it …