G ‘ail HEADQUARTERS USAF OFFICE FOR ATOMIC ENERGY ,DCS/C AFOAT=} } " glté 1453 24 April 1953 4 MAY 1953 MELORANDU:; FOR RECORD sect: MMR Height of IVY (Rggggg ike Cloud le At the time of the IVY Mike Operation two eircraft designated “Saltshaker” flew race-track courses, one due south of ground zero at approximately 70 nautical miles, the other due east of ground zero at epproxinctely 60 nautical miles. The planned mission of these flights was to secure a photcgraph of the IVY Mike cloud each minute for one heur folloving the explosion. This mission was requested by Headquarters USAF, AFOLT-1 for after~the-fact cloud height calculations but the pictures heve not yet been received, and may not be of much value for the intended purpose becouse of pocrly defined or absent horizons. 2, Unscheculed bubble sextant readings vere made by Dr. ft. D. Urry in the aircraft to the south and Colonel Fee of Headquarters USAF, AFUAT-] in the aircraft to the east. Aircraft loran positions were provided by the nevigator of the aircraft who also checked some cf the angle observations. Attached heretc is Table I giving the cbservations and calculations of cloud heisht end heights of various outstanding features of the cloud. The obser vetions ef angle, distance to ground zero, and aircraft altitude are belicved tc be such that the calculated heights are not in error one way or the cther by mere than a few thousand feet. Consideration of some points vould lead one te believe that no large errors were introduced by “edge” sighting and thereby obtaining erroneously high angles. First of all, there can be little ef this kind cf error in sighting on the rather sharp-peinted plume which yielded an altitude of 135,500 feet. The difference between this altituce and the top of the cloud at around 120,000 feet was in the ccrrect propertion to the thickness of the cloud (120,000 - 67,000 = 43,000 feet) as judged at the tire. Seccndly, a sighting on the far right edge of the cloud (cbs: at 11.75 minutes in Table I) gave 104,000 feet and this can hardly be in error by 40,00 feet due to erroneous sighting arising from edge and thickness effects, as it would be if the cloud did not rise above the tropofeuSsce Thircly, the main shear layer measured at 15.25 minutes in Table I géve an altitude corresponding exactly to that of the prognesticated princi shear altitude for the event and was again judged toe be at the ccrrect properticns] altitude fer a top et around 120,000 feet. Fourthly, the altitudes ez 116,000 and 112,000 feet at 2.66 and 3.42 minutes are not explainable on false base line because of lateral movement of the cloud; air movements are net that rapid compared with a plane to greund zerc base line of 68 nautical rN. rles. Inclosure ) 1 Copied/DOE LANL, J-Div. we ee ee ee ee rree ~