ete
pote
reayois
flee
b,o
Mae,
be the
ese
c
‘
.
te fore
ite on be
pp.
fh
ot
o.r
oy
‘
Soy
hoe
rg,
Loo3
to
ig inc rtrist to low aititude toe oath es > uhere tha Toth ly of the,
he Hinitiig ‘orlrestal 4 te
ergy is slower and the attenvation greater.
at
round|igvel for minimal
burns was fou:nd to_ be 300 nv t{cal
mfles for
wee
oe oar +
Powae
iain: ain«ain
ossa
The size and severity of the lesion correlated “with distance.
Correspondingly
greater limiting distances would apply if the exposure was at altitudes where
there would be proportionally less atmospheric attenuation
All burns produced within 160 nautical miles would have produced permanent injury or at
least a segmented visual defect in man. Visual acuity would have been reduced to from 20/100 to 20/200 if the lesion should occur on the macula.
Projects 6.5 and 6.6 utilized ground based service radars to study the
feasibilfty of determining fireball and cloud parameters, respectively, for
very high altitude shots.
Both had pursued similar objectives during earlier
surface shots at Eniwetok.
The returns from shot Teak were of short duration and did not appear
until about H + 1 min, indicating initial absorption followed by reflection
from the region of high electron density caused by the fireball.
Although
there are still attendant problems, location and yield determination for sur-
face bursts using ground radars appears feasible; however, insufficient data
were obtained to determine whether such detection is practical for very high
altitude bursts.
The cloud detection experiment during the earlier surface bursts was
a continuation of work done on Operations Greenhouse, Redwing, and Plumbbob.
It appeared that X-band radar was applicable to cloud detection for surface
or near~surface bursts. For these, the range of detection is the line-ofsight distance, the detection duration is four to six tim2s longer in humid
(EPG) areas than in arid (NTS) areas, and cloud parameters can be measured within the accuracies of the equipment. For bursts above a 90,000-ft
altitude, the lack of sufficient moisture or particle density and the level of
electron density precludes detection of the cloud by X-band, ground based
radars.
Project 6.11 measured the absorption and induced ionization effects of
very high altitude detonations with an aim toward resolving anticipated problems of high powered ICBM detection radars. Five discrete frequencies from
10 to 1000 Mc were utilized in specially constructed radars.
Riometers
were used to detect absorption by measuring any depressions in the integrated cosmic noise;
with these, 30-, 60-, and 120-Mc frequencies were used.
It was found that increasing the altitude of the shot radically increases
the ionization and absorption effects in the region of 10 to 1000 Mc. Shot
Teak, and to a lesser extent shot Orange, strikingly resembied a man-made
auroral display observable both visually and with radio equipment, similar to
the natural aurora that has been studied with the same techniques in Alaska.
At altitudes such as that of shot Teak, considerable high frequency communication blackout occurs, and absorption on the order of minutes occurs near
the shot even at ultra-high frequencies. Clutter from the shot-caused aurora
would be of concern to a radar operating in the vicinity.
Project 6.12 investigated the nature of radio frequency attenuation
through the ionized region produced by very high altitude detonations. Rockets
carried L- and S-band pulse carrier radio transmitters to above burst altitudes. Definite changes in signal were noted as the transmitters entered the
region of the burst, although the signals were not completely lost. It was
42
t
=
Arac/ng
4