ABSTRACT
A total of 17 stations, one close-in (320 km from Bikini and 23 km
from Eniwetok) and the balance at distances, were operated for the
AFOAT-1 electromagnetic experimental effort. Seventy-four sets of data
were obtained from a possible total of 102.
Of the remaining 28 sets,
no data were obtained because equipment was not in operation, records
were not readable, the alert notifications were not received, signals
were not discernible, or equipment malfunctioned.
Broad-band (close-in, up to 40 Mc; at distances, about 100 ke) and
narrow-band (about 200 cycles) measurements were made of the vertical
field component. Close-in waveforms and field atrengths were recorded
for all shots except the first. Signals were received and waveforms,
field strengths and azimuths were recorded at distances exceeding
12,000 Im for both a north-south and an east-west path.
Spectrum analyses of the frequency con~
tent of the close-in waveforms confirm the theoretical conclusion that
the predominant frequency becomes lower as the yield increases, For a
nuclear weapon in the 10-Mt range, the predominant frequency is about
8 to 10 kc, while in the 100-kt range it is about 18 to 20 ke.
Analyses of broad-band pulses’ received at distances show that the
higher frequencies are attenuated relatively more and, when received at
several thousand kilometers, the close-in differences largely disappear.
An approximation of yleld may be obtained at distances by measurement
of peak fleld strengths.
Where equipment capabilities permitted, times of detonation—-~after allowing for travel time of the nuclear detonation signals and
standard time signals—--were measured to within 2 msec, with one exception.
Transmitting stations in the very low frequency band were monitored
at selected intervals. Generally, a north-south path crossing the
auroral zone shows greater attenuation than an east-west path of equi-
valent distance,
.