TM 5-805-4/AFJMAN 32-1090
Table 5-1. Molecular Absorption Coefficients, dB per 1000 ft., as a Function of Temperature and Relative Humidity.
Octave Band Center Frequency, Hzb
Relative
Temperature
Humidity
F
C
$
63
125
250
500
1000
2000
4000
8000
14
-10
10
0.3
0.5
0.6
0.9
1.2
1.8
2.8
4.0
50
0.1
0.2
0.6
1.6
4.4
8.6
13.9
17.0
90
0.1
0.1
0.3
0.9
2.6
7.2
18.3
26.6
32
0
10
0.2
0.6
1.3
2.4
3.5
4.8
6.9
8.9
50
0.1
0.1
0.3
0.9
2.6
7.5
20.3
32.9
90
0.3
0.1
0.1
0.6
1.4
4.1
12.1
21.9
50
10
10
0.1
0.3
1.0
2.7
6.5
11.9
17.5
21.1
50
0.1
0.2
0.3
0.7
1.6
4.4
13.3
24.0
90
0.1
0.2
0.3
0.7
1.3
2.8
7.3
13.3
59
15
10
0.1
0.3
0.8
2.3
6.1
14.4
25.9
32.6
30
0.1
0.2
0.4
0.8
2.0
6.1
17.7
31.6
50
0.1
0.2
0.4
0.7
1.5
3.6
10.5
19.3
> ("Std Day")
70
0.1
0.2
0.4
0.7
1.5
3.0
7.6
13.7
90
0.1
0.2
0.4
0.7
1.5
3.0
6.6
11.2
68
20
10
0.1
0.2
0.6
1.8
5.3
14.2
31.9
44.9
0.1
0.2
0.4
0.8
1.8
4.8
14.4
26.2
30
50
0.1
0.2
0.4
0.8
1.6
3.4
8.6
15.6
70
0.1
0.2
0.4
0.8
1.6
3.3
7.1
11.9
90
0.1
0.2
0.4
0.8
1.6
3.3
7.0
10.8
77
25
10
0.1
0.2
0.5
1.5
4.4
12.4
33.5
52.6
30
0.1
0.2
0.4
0.9
1.8
4.1
11.6
21.7
50
0.1
0.2
0.4
0.9
1.8
3.6
8.0
13.4
70
0.1
0.2
0.4
0.9
1.8
3.6
7.6
11.7
90
0.1
0.2
0.4
0.9
1.8
3.6
7.6
11.7
86
30
10
0.1
0.2
0.5
1.2
3.6
10.4
29.3
50.7
50
0.1
0.2
0.5
1.0
2.0
4.0
8.3
12.9
90
0.1
0.2
0.5
1.0
2.0
4.0
8.3
12.8
100
38
10
0.1
0.3
0.6
1.1
2.7
7.7
23.0
41.3
50
0.1
0.3
0.6
1.1
2.3
4.6
9.6
14.6
90
0.1
0.3
0.6
1.1
2.3
4.6
9.6
14.6
Taken from "Standard Values of Atmospheric Absorption as a function of Temperature and Humidity,"
SAE ARP 866A, 15 March 1975, Society of Automotive Engineers, Inc., 400 Commonwealth Drive,
Warrendale, Penn. 15096.
b
Use 0 dB/1000 ft. for 31 Hz octave band.
Used with permission from Society of Automotive Engineers, Inc.
upward into the sky and does not return to earth)
1000 feet or more). In summary, downwind can
is bent down and returns to the earth, sometimes
reduce or eliminate some of the attenuating effects
passing above the attenuating ground surfaces and
of terrain and vegetation or of solid barriers that
the vegetation, thus yielding higher sound levels
otherwise intercept sound paths.
to the receiver. This can occur only for relatively
large distances between source and receiver (say,
condition can cast a shadow zone, as shown sche-
5-3
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