OPERATION HARDTACK I - DATE: TIME: PPG Time Poplar GMT 12 July 1958 1530 Sponsor: 12 July 1958 0330 SITE: UCRL PPG - Bikini - SW of Charlie, 7,500 ft from the nearest edge of island 1i° hit 165° 15' 17" 5o" Site elevation: HEIGHT OF BURST: N &§E Sea level 11.66 ft TYPE OF BURST AND PLACEMENT: CLOUD TOP HEIGHT: Surface burst from varge on water over reef > 61,000 ft MSL CLOUD BOTTOM HEIGHT: 42,000 ft MSL REMARKS: Only individual island dose rates are available. These were obtained from the Radiological Safety organization helicopter surveys at H+4 hours. The helicopter survey technique called for the pilot either to land the aircraft at the desired spot, so that a ground reading could be obtained, or to make a slow pass over the desired spot at an elevation of 25 feet. Readings taken at 25 feet were multiplied by a factor of 2 in order to obtain a reasonable approximation of the true ground reading. The basic instrument used in the aerial surveys was the AN/PDR-39 survey meter modified to read up to 500 r/hr. The t-!*? decay approximation was used to extrapolate the H+ hour dose rate readings to H+] hour. 286