Chopfer 7 LONG-RANGE DETECTION Program 7 consisted of three projects to investigate the problem o. long-range dctection of nuclear explosions. The problem divided itself essentially irto two major parts: (1, detecting and locating the explosion and (2) documenting it to the maximum extent possible with regard to type ti.e., fission, fusion, cr co:nposite), yield, design. etc. Each project attacked the problem from a different aspect and with certain inherent limitations and capabilities. Project 7.1 investigated the electromagnetic radiations, Project 7.2 investigated airborne low-frequency sound, and Project 7.4 investigated solid, liquid. and gaseous debris resulting from nuclear explosions. A discussion of the findings of these projects follows; details on their test procedures are summarized in the Appendix. 7.1 ELECTROMAGNETIC EFFECTS Experimental measurements of the elcctromagnetic pulse emitted by a nuclear detonation had been made during each series of nuclear tests beginning with Buster-Jan,ic. From those experiments, the following cunclusicns had been drawn: 1. There is an electromagnetic pulse less than 100 yser long emitted at the time of a nuclear detonation; at a distance of 20 kin. frum the generating source, its field strength may be a few hundred volts per meter. A general relationship exists between kilotcen yield and the electroniagnetic energy emitted. 2 The emitted frequency spectrum extends from about two kilocycies or below up to atiew megacycles, but the main components are in the region of about 6 to 50 kc, with an approximate inverse relationship between yield and predominant frequency. 3. Pulses received close-in—approximately 20 km—exhibit very-short rise times of less than a microsecond in a negative direction (i.e., the electric field vector is downward). The pulse is predominantly vertically polarized. 4. Even low-yield devices can produce a pulse receivable at distances in excess of 1,000 km. Close-in reception indicates that certain nuclear~-device characteristics can be determined from pulse fine structure. 5. The ground wave is generally not detectable beyond about 1,500 km from the source because the ionospheric sky wave predominates Close-in fine structure disappears during sky-wave propagation to distances. 6. A fix of the source of the pulse can be obtained with direction-finding equipment. Observed azimuthal errors using equipment tuned to 10 ke are between 0 and 9 degrees; most errors are less than 3 degrees. 7. At distances, the pulse is extended to approximately ten times its close-in length, the result of multiple arrivals by various paths each characterized by one or more ionospheric reflection. To further this work, Castle Project 7.1 had the following objectives: (1) determina- | tion of pulse character before changes due to propagation became apparent; (2) determina= tion of pulse character as a function of external parameters such as distance, time of day, and ionospheric conditions; (3) measurement of field strength; (4) explanation of the causes of the electromagnetic phenomena observed; (5) determination of the relation of 92