ABSTRACT
The variation in the transmission of the atmosphere over an optical
path passing 2900 ft from ground zero of Nectar{Mike crater) was measured as a functionof time by a modified high-speed spectrograph located
at Engebi in Station 1841.
The spectral resolution “was about 75A at
4000A and the time resolution was about 800 psec. The spectrograph
looked with a narrow field of view at two 60-in. carbon-are searchlights
tg
‘on Ruchi.
The spectrograph and searchlights were timed so as to start
running betore zero time.
in this way a reference base was o
from which variations in the atmospheric transmission over the 35004500A region could be measured.
Sensitometry of the photographic data obtained reveals that, except
for some Teller emission either scattered or induced in the atmosphere
betweenthe source and the spectrograph, transmission of the atmosphere
in the abeve wavelength region started to decrease immediately after
zero timne, but that stable values were not reached until after about 50
cctterane
msec had elapsed.
These values thereafter remained essentially con-
stant until the fireball intersected the field of view of the spectrograph
at about 435 msec pastzerotime. The transmission declined by approxi-
mately 1.2 density units (D.U.) at 4300A.
At shorter wavelengths the