s
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 in Figure 2.9.
TABLE 2.3
Station
Number
170.01
The air-induced signal
ACCELERATION DATA
Oround
Range
Get
Range
c
component
Ground-Transmitted
Arrival
Maximam
Maximum
sec
6
8
Time
Positive
fr
5
2,596
33
33
3
Vv
R
T
0.31
0.31
0.06
150
Negative
Accoleration
Fre
Temy
cps
Air-hock Induced
Arrival
Maximum
Maximum
Frequency
sec
time
Positive
Negative
s
6
ops
0.47
1.27
No Record
42
0.63
45
0.68
3.44
2.20
4.16
4.67
0
100
170.03
3,650
a4
mu“
8
Vv
R
t
0.39
0.40
0.42
0.37
0.13
0.21
0.25
0.35
0.19
~
_—
_
1.24
1.23
1.24
0.23
0.62
0.24
0.86
0.29
0.18
&
_
_
196.02
5,699
9
9
v
Rg
061
0.61
0.17
0.18
0.15
042
38
_
2.63
2.856
0.18
051
0.81
0.26
_
3
T
0.61
0.10
0.10
~
2.61
0.16
0.28
_
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 meansof integration of the acceleration traces was not attempted because the quality of the data was too poor to support such analysis.
structural damage.
2.6
Also, the ground motion was too small to produce significant
UNDERWATER MEASUREMENTS
Propagation of shock waves in shallow water was not well understood. Crossroads
Baker and ivy Mike had been instrumented with underwater measurements. Baker re-
sults 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 submarinein shallow
water, (2) an attack against ships in harbors as well as the harbor facilities, and (3) attacks 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-
83