culated from the ideal curve. It was also possible that dynamic pressure might assume added significance with the high-yield devices because uf the increused positive-phase duration. 2.3.1 Overpressure. A fact of major significance noted on the records of both aver-~ pressure and dynamic pressure was the non-ideal shape of the wave forms. It had been thought —the possibility of precursor notwithstanding—-that considering the long diztances of water travel inherent in the instrumentation of long blast lines at the proving ground, most wave shapes would appear nearly as the ideal: a fast rise followed by a TABLE 2.1 SCALING FACTORS Shot and Environment 1 (Surface, 2 (Surface, 3 (Surface, 4 (Surface, 5 (Surface, 6 (Surface, ,.eald, Mt Po, mb 15.0 1006.1 11.6 1012.4 0.130 1009.7 7.0 1007.4 13.0 1010.8 1.7 1006.4 Po, pal To. F 14.58 90 0 14.67 80.0 14.63 81.0 14.60 810 14.65 80.8 14.58 79.9 To, € Sp 8g & x 26.66 1.0078 0.0408 0.0409 G.0412 26.66 1.0916 1.0450 9.0456 0.0455 27.22 1.0046 0.1973 Q.1957 0.2006 27.22 1.0068 0.0522 6.6528 9.0631 27.12 1.00358 0 0426 0.0430 0.0432 26.61 1.0078 0.0836 0.0845 0.0854 Reef) Crater) Land) Lagoon) Lagoon) Crater} smooth decay. This was not observed. A typical series of overpressure records is shown in Figure 2.1. The low-pressure records, after an initial sharp rise, exhibit a continuing slower rise to peak before the decay—~a hump-back appearance. In the high. rpressure regions, this second rise is not prominent; however, the front is rounded and peak pressures are smaller than would be obtained by extrapolating the decay back to the arrival time. The cause appears to be associated with the water-laden medium through which the blast wave was propagated: specifically, the water cloud picked up by passage of the shock over the water surface. Shock photography along the surface showed what appears to be spray behind the shock fronts, particularly on Shots 2 and 4. It may be concluded that water does not constitute or approximate the idea! surface——it sometimes had been assumed asideal. Precursors that could be identified as such were not observed on any of the records. Two shots on which this phenomenon might have been detected were modified: one was cancelled entirely and the other experienced a much-~lower yield than planned and instrumented for. 2.3.2 Dynamic Pressure Free-Field Measurements. Various types of gages were selected for those measurements, recording either dynamic pressure, q, directly or some related parameter—density, temperature, total pressures—-that would aid in the interpretation of results. All gages were placed 6 feet aboveground, a compromise to eliminate interference effects from the ground yet allowing a strong enough mountto withstand the high dynamic pressures. Gages were placed on each shot to span the 10to-40-psi range of overpressure. Self-recording gages mounted 3 feet above groundlevel were also located in this pressure range. Participation on Shots 1 and 2 was a minimum effort, and the low yield of Shot 3 precluded effective results. Shots 4 and 5 gave dynamic pressures higher than those computed from the measured overpressure. As in the overpressure records, the wave forms 24