early moments subsequent to time zero. Later pictures show the shock wavealong the water surface as it progressed outward from site zero. , To extract IBDA data from the photographs, large-scale graphics were prepared to achieve greater accuracy in interpretation. Site zero was established within an accuracy of 600 to 1,100 feet from the actual location by determining the center of curvature for the horseshoe configuration. Interpreters attempted to obtain yield data from the photo- graphs by utilizing time-distance curves that indicate the progress of the shock wave TABLE 6.7 AIRCRAFT POSITIONS Smot i 2 3 34,000 15 33,000 18 32,000 12 31,000 23 31.000 23 30,006 30,000 4 8 6 _ —_ 32,000 15 32,000 12 31,000 20 31,000 23 — _ 31,600 20 30,000 30 ,000 30,060 30 ,000 B-60 No. 1 Altitude, ft Distance, naut mi B-8C No. 2 Altuude, ft Distance, naut mi B-50 No. $ Altitude, ft Distance, naut mi 30 30 27 30 30 37 outward from ground zero for various yields. Computations of yield by this method proved inaccurate. Since participation was limited to surface bursts, no attempt was made to obtain height-of-burst information. 6.4 IONOSPHERE STUDIES Project 6.6 was conducted to study the effects of megaton-yield-range detonations on the ionosphere Following Shot Mike of Operation Ivy, it was noted that the virtual height of the F~2 layer greatly increased. The project desired to corroborate this phenomenon and to study the cause-and-effect relationships associated with it. It was also desired to obtain data on effects at large distances from the detonation to ascertain the possibility of using such effects as a means of long-range detection. For collection of data, two ionosphere recorders were operated in the Marshall Islands: one at Parry Island 200 miles west of Bikini and the other at Rongerik Atoll 150 miles east of Bikini. In addition, normal data from existing stations at Maui and Adak and special data from existing stations at Guam and Okinawa were studied to determine ef- fects at distances of 1,400 to 3,000 miles. At Parry Island, severe absorption occurred for several hours following all megatonyield shots. This phenomenon wasattributed to ionization resulting from radioactive particles carried to the west by fast winds at altitudes of 60,000 to 120,000 feet. Turbulence in the E-region after megaton-yield shots was manifested by sporadic E-returns detected at Rongerik. In the F2 layer, an effect similar to that observed during Ivy was noted, but its nature varied from shot to shot. Apparently the movement of electrons in this layer was far more complex than originally assumed, but was still attributable to & large-scale convection resulting from the conversion of blast-wave energy into heat in the upper atmosphere. Data from the distant stations indicated that ionospheric disturbances were propagated up to 2,600 miles from the points of detonation at velocities between 8 and 16 km/min. It appeared that the duration of the disturbances was related in some manner to the yield of the device and was about inversely proportional to the distance. 91