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