ing them at the same sites would have severely limited any effort to measure true craters
by coring and drilling. In the case of the crater from Shot 3, any such extensive operation would have been long deferred because of radiological safety considerations.
in determining the depth of craters, both sonic fathometer and lead-line sounding
measurements were utilized. it is pertinent that the fathometer survey of the Shot 1
crater showed a uniform flat bottom at a depth of 170 feet; however, thig flat bottom undoubtedly represented the upper surface layer of mud and suspended sand which wag get-
tling in the crater.
TABLE 4.1
By contrast, lead-line soundings taken at approximately the same
CRATER SURVEW DATA
Ali reauits are based on fathometer, lead line soundings, and aerial surveys. There was branching of the reef to the lagoon
side for Shots 1 and 3.
after
Aarial
Pathameter
Height of
Preshot
Water
Depth at
tt
ft
craier
Crater
Shot
Tocation
Yiold
ft
ft
x
Coral Reef
15.0 MB
0
7
15.4 above
3
&,000
240
3
laland
130 kt
1
24
23.6 above
ground
4
840
78
160
3,000
8
5
C.QG. of Device
water
16.3 above
Site Zero
Diameter
Depth
uip
Formation
None
§
water
20 above
MLWS8*
4
Water
7.0 Mt
(barge)
1
6
17 above
water
250f
902
None
apparent
* Mean low water springs.
1 Below wate: surface.
t Below original lagoon bottom.
{ The Shot 3 crater formed a “U” ip the island with the open end on the lagoon side. There was no lip apparentat the time of
survey in the shallow water of the open face of the “U.” On the land around the crater, Up formation was fragmentary aod
nad one peak extending 30 feet above the original ground level. In general, the lip was lese than 16 feet above the origins)
ground level; however, the water wave [rom Sbot 4 had completely inundated the lip before the lip survey was made.
time recorded a depth of 240 feet, which is considered to be the Shot 1 depth of crater.
This emphasizes that when there is suspended material in the water, the use of the sonic
fathometer is unreliable and not recommended.
Yable 4.1 indicates the general reguits of this crater-survey project.
One of the most significant aspects of Project 3.2 was that the crater-survey results
caused serious questions to be raised (in the project report, WT-920) regarding the validity of the usually accepted cube-root scaling for prediction of nuclear-crater radii. This
point stimulated considerable study, evaluation, and differences of opinion prior and subsequent to the publication of WT-920.
However, after considerable additional study of existing high-explosive and nuclear
crater data, an AFSWP report was published (Reference 10) which clarified the prior
differences of opinion by carefully cataloged conclusions in favor of the continued use of
the cube-root scaling procedure for predicting crater radii. Significant conclusions of
Reference 10 regarding crater predictions were: (1) For a given energy release, the
cratering effectiveness of an explosive charge will in general decrease with increasing
energy density. (2) A common soil factor of 1.8 to 2.0 should be used in conjunction with
TM 23-200 (Reference 7, Figure 32, crater-radius prediction curve for dry soil) as the
ratio between scaled crater radii at the EPG (washed soil crater) and the Nevada Test
Site (dry soil crater) for both high-explosive and nuclear-device craters. (3) The cuberoot scaling law can be used for prediction of crater radii, whereas the scaling relation-
65