F.3 Gaseous absorption for a troposcatter path

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 h_rho = h_ts, q_elev = q_tpos, d_cv = d_tcv , 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 h_ts, q_tpos, and d_tcv 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 h_rho = h_rs, q_elev = q_rpos, d_cv = d_rcv 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 h_rs, q_rpos, and d_rcv 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 h_rho masl, elevation angle of path q_elev mrad, and horizontal distance to the common volume d_cv 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, A_o, A_w and A_wr, 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 d_o and d_w for oxygen and water vapour:

(F.4.1a)

(F.4.1b)

Calculate the effective distances d_eo and d_ew 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.

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