The primary interest was in motion closer to ground zero than previously instrumented. Participation was planned for two shots, both to be detonated on atoll islands: one at Bikini, one at Eniwetok. Measurements were obtained on Shot 3; however, the unexpect- ed low yield of that event (Morgenstern) forced cancellation of the other shot (Echo) for which measurements had been planned. The instrumentation layout for Shot 3 consisted of vertical, radial, and tangential components of acceleration in the ground below the water table at ranges corresponding to 200-, 100-, and 36-psi peak air overpressure predicted for a 1-Mt yield. As a resuit of the low actual yield, set ranges for the gages were too high, recording a very~low signal amplitude. With such a low signal-to-noise ratio, the identification of phase arrivals, frequencies, and amplitudes was uncertain. The results are given in Table 2.3. The curve of arrival time versus range is shown fn Figure 2.9. TABLE 2.3 Station Number 170.01 The air-induced signal ACCELERATION DATA Ground Range Set Range c ~ Ground-Tranemitted Arrival Time Maximam Positive Maximum Negative sec € 8 f s 2,598 3s 33 v g 0.31 0.06 33 T o.81 1.50 Acceleration Air-Sbock Induved Frequency Arrival Time Maximum Positive Maximum Negative eps acc 3 £ g 0.47 No Record 42 0.63 45 0 68 3.44 4.20 4.67 100 1.87 2.20 ope oo] 176 03 3,650 ue Vv 0.39 0.37 0.28 ~ 1.24 0.23 0.66 Cty 2% .02 5,599 9 3 Vv Ra Ool 0.61 0.17 0.13 0.18 042 338 _ 2 63 356 0.28 0.51 O81 0.28 _ _ 3 T 0.61 6.10 o.10 > 2.61 0.16 0.25 u« 8 R Tt 0.40 0.43 0.13 0.11 0.35 0.19 _ _ 1.23 1.24 0.63 0.24 0.29 0.18 7 _ _ propagated with a velocity of the air blast wave, decreasing with increasing ground range. The ground-transmitted shock propagated with a velocity of about 8,700 ft/sec. The determination of velocities and displacements by means of integration of the acceleration traces was not attempted because the quality of the data was too poor to support such analysis. Also, the ground motion was too small te produce significant structural damage. 26 UNDERWATER MEASUREMENTS Propagation of shock waves in shallow water was not weli understood. Crossroads Baker and ivy Mike had been instrumented with underwater measurements. Baker results did not define the underwater pressure-time history with any degree of accuracy, but they did establish the order of magnitude of the pressure decay as a function of range. No significant data were obtained from Mike. Castle offered the first opportunity to document the underwater pressure-time history from a nuclear device detonated on the surface of the water. Actually, the geometry of ground zero for the Castle series of shots—— represented by the lagoon bottom and the atoll rim—was quite complicated, involving a condition not well understood. However, such geometry did represent conditions of practical military significance: (1) air attack against a submarine in shallow water, (2) an attack against ships in harbors as well as the harbor facilities, and (3) at- tacks against dams or mines. The specific objectives of this project included measurement of underwater pressure as functions of time, distance, and depth for large-yield weapons detonated at the sur- 33