| Annex A4.3 |
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| Pure-tone atmospheric absorption attenuation coefficients (Aat(fm) in decibels per
kilometre) and the calculated atmospheric attenuation for broadband (Aat(fm)) |
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| Frequency |
20°C, 80% |
20°C, 40% |
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| Hz |
Aat(fm) |
Aab(fm) |
Aat(fm) |
Aab(fm) |
Aat(fm) |
Aab(fm) |
Aat(fm) |
Aab(fm) |
Aat(fm) |
Aab(fm) |
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| 50 |
0.0501 |
-0.1 |
0.0965 |
-0.1 |
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0.0 |
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0.0 |
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0.0 |
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| 63 |
0.079 |
-0.1 |
0.15 |
-0.2 |
0.0705 |
-0.1 |
0.0637 |
-0.1 |
0.0462 |
0.0 |
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| 80 |
0.124 |
-0.1 |
0.231 |
-0.2 |
0.111 |
-0.1 |
0.1 |
-0.1 |
0.0731 |
-0.1 |
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| 100 |
0.194 |
-0.2 |
0.351 |
-0.4 |
0.174 |
-0.2 |
0.158 |
-0.2 |
0.116 |
-0.1 |
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| 125 |
0.302 |
-0.3 |
0.521 |
-0.5 |
0.272 |
-0.3 |
0.247 |
-0.2 |
0.1827 |
-0.2 |
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| 160 |
0.465 |
-0.5 |
0.752 |
-0.8 |
0.421 |
-0.4 |
0.384 |
-0.4 |
0.288 |
-0.3 |
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| 200 |
0.705 |
-0.7 |
1.05 |
-1.1 |
0.644 |
-0.6 |
0.591 |
-0.6 |
0.452 |
-0.5 |
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| 250 |
1.04 |
-1.0 |
1.39 |
-1.4 |
0.966 |
-1.0 |
0.895 |
-0.9 |
0.705 |
-0.7 |
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| 315 |
1.5 |
-1.5 |
1.78 |
-1.8 |
1.41 |
-1.4 |
1.33 |
-1.3 |
1.09 |
-1.1 |
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| 400 |
2.08 |
-2.1 |
2.19 |
-2.2 |
2 |
-2.0 |
1.9 |
-1.9 |
1.67 |
-1.7 |
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| 500 |
2.77 |
-2.8 |
2.63 |
-2.6 |
2.71 |
-2.7 |
2.63 |
-2.6 |
2.52 |
-2.5 |
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| 630 |
3.52 |
-3.5 |
3.13 |
-3.1 |
3.52 |
-3.5 |
3.49 |
-3.5 |
3.7 |
-3.7 |
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| 800 |
4.31 |
-4.3 |
3.77 |
-3.8 |
4.39 |
-4.4 |
4.43 |
-4.4 |
5.25 |
-5.2 |
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| 1000 |
5.15 |
-5.1 |
4.65 |
-4.6 |
5.3 |
-5.3 |
5.42 |
-5.4 |
7.17 |
-7.1 |
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| 1250 |
6.1 |
-6.1 |
5.97 |
-6.0 |
6.29 |
-6.3 |
6.48 |
-6.5 |
9.37 |
-9.3 |
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| 1600 |
7.31 |
-7.3 |
8 |
-7.9 |
7.48 |
-7.4 |
7.68 |
-7.6 |
11.7 |
-11.5 |
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| 2000 |
8.98 |
-8.9 |
11.2 |
-11.0 |
9.06 |
-9.0 |
9.21 |
-9.1 |
14.2 |
-13.9 |
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| 2500 |
0.0 |
11.3 |
-11.1 |
16.8 |
-16.4 |
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| 3150 |
15.3 |
-15.0 |
23.9 |
-23.0 |
14.8 |
-14.5 |
14.5 |
-14.2 |
19.9 |
-19.3 |
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| 4000 |
21.3 |
-20.6 |
36.1 |
-33.9 |
20.2 |
-19.6 |
19.4 |
-18.8 |
24 |
-23.1 |
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| 5000 |
30.6 |
-29.0 |
55.1 |
-49.7 |
28.6 |
-27.2 |
27.1 |
-25.9 |
29.7 |
-28.2 |
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| 6300 |
45.4 |
-41.8 |
84.2 |
-71.4 |
41.8 |
-38.8 |
39.1 |
-36.5 |
38.4 |
-35.9 |
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| 8000 |
68.6 |
-60.1 |
128 |
-98.4 |
62.6 |
-55.6 |
58.1 |
-52.1 |
51.8 |
-47.1 |
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| 10000 |
100.5 |
-82.2 |
194 |
-127.0 |
95.3 |
-78.9 |
87.9 |
-73.9 |
72.8 |
-63.3 |
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| Basing on the equation Aab(fm) = Aat(fm) [1+0.00533[1-0.2303 Aat(fm)]]1.6 from Handbook of Acoustics (where Aab(fm) is the atmospheric attenuation for broadband at frequency fm, and Aat(fm) is the atmospheric
attenuation for pure tone at frequency fm reference from ISO 9613:Part 1). |
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| As per meteorological data collected at Cheung Chau Automatic
Weather Station by the Hong Kong Observatory from September 2005 to August
2006, the maximum daily mean values at each month for air temperature and
relative humidity are 20 - 30°C and 88% - 99% respectively. Based on the above calculation for various
combinations of temperature and relative humidity that are applicable to
Cheung Chau's climate, the worst case for atmospheric absorption is at 30°C
and 100% with the least atmospheric absorption. |
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