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