recording time (in some cases, a few seconds). In order to coordinate
global operations, the day-to-day changes in schedule were sent to the
several sites over regular military TWX or commercial telephone circuits. The messages were in code when schedule information was sent.
In addition to schedule changes, the alert commmication code was used
to give estimated field strengths for the various shots and thus assist
station personnel in setting amplifier gains.
Low-frequency Interference.
The distant stations at Fort Belvoir,
Virginia and Maui, T. H. were less than 100 km from the Naval transmitters, NSS and NPM, respectively. Both transmitters use carriers
(16 to 20 ke) that would interfere with broad-band recordings of a
nuclear-device detonated thousands of kilometers away.
Through the
cooperation of the Navy, NPM, NSS and NLK were off the air at shot
times. For security purposes these transmitters were also frequently
taken off the air at other than shot times.
RESULTS AND OBSERVATIONS
There was a total of 17 stations participating, although for any
one shot no more than 15 stations were in operation. A summary of the
results at the various locations is given in Table l.
The detonation time was determined from the timing equipment on
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Parry Island, Eniwetok Atoll.
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One of the means of locating the nuclear-device pulse when recorded at distances from the test site is by knowledge of the time of det—
onation. Where millisecond accuracy was possible, the agreement, with
one exception, was within 2 msec of the Parry Island time after corrections for propagation and WWV times were made. “Some equipment did not
have the capability of resolving time to within a few milliseconds, as
indicated by asterisks in Table l.
Azimuthal errors are generally within the error experienced with
this type of very low frequency (VLF) equipment, namely, 73 degrees.
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t. An experiment at the Runit Island location, designed
to record the Teller Light and the electromagnetic pulse similtaneously,
failed on Shots 2, 3, 4, and 5 because of the distance from Bikini, and
on Shot 6 because of equipment malfunctions.
The purpose of this exper-
iment was to establish an electromagnetic fiducial in time coincident
with other phenomena.
Field Strengths. For a given path, the attenuation is determined
by distance, reflection coefficients of the fonosphere (day, night, sun-
rise or sunset along the path), and ground conductivities.
In addition,
some workers have reported variations for east-west or north-south
paths, (See the comments about the low-frequency transmitters later in
this report.)
All the above effects vary with frequency.
Up until Castle, close-in measurements had been made of the ground
wave at the Nevada Test Site at distances between 20 and 50 km, which
was within line-of-sight of the detonation areas (References 1 3)6
An
attempt was made to obtain measurements at comparable distances during
this series; however, because of the radioactive fallout from Shot 1,
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