Z a Gh Fs Mee Lioo rout he f ' 1 ef ei “a. Jf “Ty fe . tk > \ a : fot a, Vf a, 1 h 4 ' af a Lf . SAT N a _ - 1, , A 4 ‘4 . . “¢ ie Se PN LOA - z The altitudes tabulated have been computed from the telenetered ambient-pressure rec- ords, using the meteorological data taken at Bikini (see Appendix B). The slant ranges have been computed from the observed blast-arrival times and peak overpressures by using a previously computed curve giving average blast-wave velocity as a function of peak over- pressure, with corrections for the variation of sound velocity and wind component along the propagation path from shot to gauge. This method of computing the slant range is discussed in more detail in Appendix A. All differential-pressure records show the blast-wave arrival as a true shock, that is, the rise times are less than the time-resolution capability of the system, but in most cases there are small departures from ideal shock-wave shape in the form of a slight rounding off of the peak or of superimposed oscillations immediately following the shock front. The periods of the oscillations (0.3 to 0.4 sec) are far too great to be attributed to any mechanical or electrical resonances in the measuring system, but they could coincide with some motion of the canister caused by the impact of the blast on the parachute. However, the recorded variations in RF carrier signal strength show that large oscillations of the canister may take place without any corresponding variation appearing on the pressure records. It is therefore considered probable that the pressure irregularities are not instrumental but are a real property of the blast wave. It is suggested that they are caused by small-scale inhomogeneities or turbulence in the atmosphere. The largest oscillations foun. in the present case (canister No. 2) have an amplitude of about 17 per cent of the peak overpressure. Attention is called to this fact because a pressure perturbation that develops immediately behind the shock front will propagate forward with a velocity greater than that of the shock front. This will result in a variation of presaure at the shock front as successive peaks and troughs of the perturbation overtake it. ‘She possibility of an essentially random variation of this kind implies a limit to the reproducibility and predictability of peak blast overpressure as a function of distance. 3.1.2 Thermal-radiation Data The total thermal radiation registered by the successful canisters, together with their respective slant ranges, are given in Table 3.2, The time-response curves, with ordinates in millivolts output as they were read, rather than in gram calories, are given in Fig. 3.3, but they are also labeled with the integrated thermal values as in Table 3.2. In Fig. 3.3 it is shown Table 3.2-— THERMAL VALUES FOR MIKE SHOT (REVISED 20 APRIL 1953)* Array Slant range, 2 21,130 3 22,790 1 13,180 8 24,740 9 49,180 position ft Total thermal, Peak intensity, gcalem? gcealcem™’ sec"! 32 (18) 32 (22) 112 (124) 27 (23) 9 Rise in temperature of couple, C Coatingt oO 62.0 350 (210) 260 (210) 1260 A 12.0 (11) 2.0 260 (250) 90 o 17.0 (10) 12.0 (10) oO B *Values in parentheses age those obtained assuming no change during exposure in the zero between cold and hot junctions. TCoatings: O, natural, not coated; B, blackened; and A, aluminized. 24 wf RESTRICTED DATA (a SECURITY INFORMATION