2.2.2 Altity \bsorption. Because considerations of it safety limit the minimum altitude at which aircrat: can fly over water, automatic gamma monitors were mounted over the sides of two ships of Project 2.10, to measure the gamma-radiation field at 35 feet above the sea surface. This was to provide low-altitude readings simultaneous with aircraft passes in the Same area at higher altitudes. Survey aircraft made altitude-calibration passes over islands of the Eniwetok Atoll after Shot Mohawk. After Shot Tewa, the P2V-5 dropped a smoke light in the open sea to be used asa navigational reference and made altitude passes in the vicinity. These data are examined for the variation of radiation reading between different flight altitudes and given in Section 3.2. Helicopter missions, after Shots Seminole and Mohawk, obtained data similar to the altitudecorrection-calibration data collected by the survey aircraft. Because the helicopters could not safely hover at lowaltitudes, complete information could not be obtained. It had been planned to obtain gamma-energy spectra at various altitudes above a contaminated surface. The Top Hat dose-rate response was to be compared to the gamma-energy spectra to determine whether the assumption of air-equipment response was valid. However, instrumentation difficulties and the limitations in hovering altitudes resulted in fragmentary data. The survey using a scintameter obtained dose-rate readings at altitudes between 25 and 1,000 feet. 2.3 INSTRUMENTATION The major instrumentation consisted of aerial radiation detectors. Scintillation survey meters and ship-mounted gamma monitors were used for measurements relating to altitude-correction factors. A spectrometer was used to obtain the distribution of the gamma energies at survey altitudes. 2.3.1 The instruments are described in Appendix B. Aerial Survey. Each of the project aircraft had the following equipment: (1) Top diet aerial radiation detector, HASL TH-10-B (Appendix B); (2) detector control assembly, HASL TC-14-A; (3) strip-chart recorder, Esterline Angus Co., AW; (4) telemeter assembly, HASL TT-3-X; (5) power supply, HASL TB-6-A; and (6) radio transmitter, U.S. Navy ART-13. The permanent components were installed by the Overhaul and Repair Department, U.S. Naval Air Station, Alameda, California, at the air station prior to Operation Redwing. The removable components were installed by project personnel after the squadron deployed to the EPG. The location of the assemblies is indicated in Figure 2.3. The radiation detector was mounted aft to avoid the major areas of aircraft contamination, namely, the engines, oil-cooler air intakes, leading edges of the wings, propellers, and front of the radome. were Sealed to prevent contamination of the interior ductwork. The cabin intake vents The control assembly and the operator were placed forward, next to the navigator. This facilitated close correlation between the navigational and radiation reports. The remainder of the equipment was located on an available-space basis. The relationship of the various sections, both in the aircraft and in the Program 2 Control Center, is shown in Figure 2.4. The radiation detector and its associated control assembly drives a strip-chart recorder to provide a permanent, continuous record of the radiation intensities as measured in the aircraft. Figure 2.5. This detector is nearly air-equivalent from 30 to 1,400 kev. An annular radiation shield is built into the detector to reduce the effect of aircraft contamination. The angular response due to this shield is shown in Figure 2.6. The aircraft’s radio altimeter (U.S. Navy APN-1) supplies an altitude indication to the altitude compensator, which modifies the radiation detector so that its output is a current that is propor- tional to the radiation which would be measured at 3 feet above the surface. As the altitude changes, the compensator corrects the resulting radiation change and keeps the ground-level reading constant. DOE ARCHIVE The telemetering system did not perform satisfactorily. The radiation readings on the aircraft radiation-detector strip-chart recorder were, therefore, transmitted by voice over the navigational net. At the control center, the radiation readings were logged and immediately plotted, 19 = Ib