.u; a:s:e!T
II EXlSTE'iCE OF A SOU:m CHAN:fEl iN TRF AT"'C~PHERE
In ~eptember, 1944, 1 t occurred to me that there
is a s1~1lar sound channel 1n the atmosphere with the axis
at a height of about 45,000 teet, and that, with eource and
receiver plsced at th1e height, we might exceed the accepted
range.!! a a enormously UJ we had tn the ocean. ln other wot"da,
it might be -poat~ib~.e to detect sound halt way aro•.1nd the world.
~: ..
The fundamental data on this subject as revealed_dur1ng
a hur~ied search of the literature (mostly nrior to 19~0), ahow
that, for a t:voical large exoloe1on, there is at:dibility from
0 to 25 miles an1 froM 90 to 125 miles, with a zone of silence
from 25 to ~0 ~1lee. The accepted explanation of the total
collection of these dat:t is tbat tt1e 5T)eed of sound deore:ases
fro"'- about l 090 tt/see at the ~urtace to about 970 ft/sec at
about 45,000 feet, a:::d tt:cn inc:reases to abo:1t 1165 ft/sec
at a~ut 130,000 feet. (Reference 2)
Thu~ there 1~ a ~oun1 ~hannel in the atmosphere
with its axis at a ~ei;bt of aco~t 45,000 feot, nnd if both
sound source and 7-'aceiver are located at th!:: height, ".te
!!WY a.x:;>ect extr:aoro1nary !'lilnges and all the othor nseful
~heno~ena which have been found in the sound channel ln
the ocean. This means that the signals will have highly
eharaeter1st1c 1dent1fy1ng features anj that they will permit
aeou~te tr1an~ulat1on.
III ?ROBABLE 7lAXIJ:UM F\A~lGE
'l'he maxlmul'll N.nge ror sonic signalling 1n the
ataoapher1o aoum ehannel.w111 :1epend pr1Dt&r1ly on the
absorption coeff1c1ent, which 1a .the rate at wblcb the
acoustical energy 1a converted 1nto heat_by fr1ct1onal los~ea.
•ollow1ag Rayleigh (Rete~ence 3, P• 316), it MAy be calculated
that· the distance at Wb1ob·eound of.trequency 50 cycles ~er
aecoDd would be reduced 1n 1ntena1ty by the !aotor 7.5 by
the ettect or t'r1otion alone 1a about 24,000.m1lea at sea level,
aDd about '500 allea at 45,000 feet~ Aa these d1atancea
are ·1nverflely proportional to tbe square or the frequency,
they would be one hundred t1mes greater tor sounds of fJ"equeney
5 oyele., oer •econd, wbioh ha•e often 'been o'bee~ved when
large ex~loa1ona we~e •tud1ed.
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