This section gives the method for calculating gaseous absorption for a complete troposcatter path, from transmitter to receiver via the common scattering volume.
Use the method in § F.4, with hrho = hts, q elev = q tpos, dcv = dtcv, to give the gaseous attenuations due to oxygen, and for water vapour under both non-rain and rain conditions, for the transmitter/common-volume path, where hts, q tpos, and dtcv appear in Table 3.1. Save the values calculated by equations (F.4.3a) to (F.4.3c) according to:
dB (F.3.1a)
dB (F.3.1b)
dB (F.3.1c)
Use the method in section F.4, with hrho = hrs, q elev = q rpos, dcv = drcv to give the gaseous attenuations due to oxygen, and for water vapour under both non-rain and rain conditions, for the receiver/common-volume path, where hrs, q rpos, and drcv appear in Table 3.1. Save the values calculated by equations (F.4.3a) to (F.4.3c) according to:
dB (F.3.2a)
dB (F.3.2b)
dB (F.3.2c)
The gaseous attenuations due to oxygen and for water vapour under both non-rain and rain conditions, for the complete troposcatter path are now given by:
dB (F.3.3a)
dB (F.3.3b)
dB (F.3.3c)
F.4 Gaseous absorption for terminal/common-volume troposcatter path
This section gives the method for calculating gaseous attenuation under non-rain conditions for the path from one terminal to the common volume of a troposcatter path.
The inputs are height for water-vapour density hrho masl, elevation angle of path q elev mrad, and horizontal distance to the common volume dcv km.
The outputs are the attenuations due to oxygen, and due to water vapour under both non-rain and rain conditions, for the terminal/common-volume path, Ao, Aw and Awr, in dB.
Obtain surface water-vapour density r sur at the terminal from the data file “surfwv_50_fixed.txt”.
Use equation (F.6.2) to calculate the sea-level specific attenuation due to water vapour under non‑rain conditions, g w, dB/km.
Use equation (F.5.1) to calculate the surface water-vapour density under rain conditions, r surr, g/m−3.
Re-evaluate r sur according to r sur = r surr.
Use equation (F.6.2) to calculate the sea-level specific attenuation due to water vapour under rain conditions, g wr, dB/km.
Calculate the quantities do and dw for oxygen and water vapour:
(F.4.1a)
(F.4.1b)
Calculate the effective distances d e o and dew for oxygen and water vapour:
km (F.4.2a)
km (F.4.2b)
The attenuations due to oxygen, and for water vapour under both non-rain and rain conditions, for the terminal/common-volume path are now given by:
km (F.4.3a)
km (F.4.3b)
km (F.4.3c)
where g o, the sea-level specific attenuation due to oxygen, appears in Table 3.1.
