concluded that such signals are attenuated, but not.to the extent that prior theoretical calculations had predicted. Program C: Airborne Measurements of Thermal and Electromagnetic Phenomena There were six projects in Program C: four investigating thermal phenomena (Projects §.2, 8.3, 8.4, and 8.5) and two studying electromagnetic effects (Projects 6.10 and 6.13). Six aircraft were used, three equipped with thermal instrumentation and three with electromagnetic equipment. All projecta were successful on both shots. For shot Teak there was a single thermal pulse lasting Most of this energy came from molecular emission bands rather than from the blackbody radiation common to surface or near-surface bursts. The infrared radiation was intense but brief--about maximum radius of the infrared fireball was almost in duration. The The thermal pulse from shot Orange showed some of the characteristics of a sea-level shot. There was some evidence of a minimum and a second maximum. Some of the energy was radiated in a continuous spectrum, in addition to spectral bands similar to those from Teak. The infrared emission lasted about and the infrared fireball radius reached a maximum of about Radar echoes from the ionized cloud were received by two of the aircraft. Returns were observed on UHF band radars for a period of about an hour for both Teak and Orange. One of the aircraft also carried atmospheric sounding equipment and measured disturbances of the ionosphere produced during both shots. It was found that the electrical properties of the ionosphere were disturbed in excess of 4 hr out to distances of several hundred miles. 2.2 TASK UNIT 1, LASL PROGRAMS Task Unit 1 carried out experiments to determine device performance, to measure physical quantitiea of interest in weapon design, and to understand the mechanisms by which the various effects of the devices are produced. In Operation Hardtack new methods were used to determine the configuration of the active material during the reaction period. Programs 10 and 18, Fireball Physics and Thermal Radiation The objectives of these programs were: (1) to determine the yields of the devices by observation of the various parameters associated with fireball hydrodynamics; (2) to measure the time interval between primary and secondary reactions in two-stage devices by optical means; (3) to study the phenomena taking place in the rarified air on two high altitude shots of about ‘yield; and (4) to measure total thermal radiation and thermal power on ume wwo very high altitude detonations. Oscilloscopes and photomultipliers with optical narrow pass filters were used to record gamma-induced light from the air about two-stage devices. Photomultipliers and oscilloscopes with high time resolution were used for observations of narrow bands of the optical spectrum. 43