D.2 Point incidence of ducting

Calculate a parameter depending on the longest inland section of the path:

(D.2.1)

Calculate parameter μ₁ characterizing the degree to which the path is over land, given by:

(D.2.2)

where the value of μ₁ shall be limited to μ₁ £ 1.

Calculate parameter μ₄, given by:

(D.2.3)

The point incidence of anomalous propagation, β₀ (%), for the path centre location is now given by:

(D.2.4)

D.3 Site-shielding losses with respect to the anomalous propagation mechanism

Corrections to transmitter and receiver horizon elevation angles:

(D.3.1a)

(D.3.1b)

The losses between the antennas and the anomalous propagation mechanism associated with site‑shielding are calculated as follows.

Modified transmitter and receiver horizon elevation angles:

mrad (D.3.2a)

mrad (D.3.2b)

Transmitter and receiver site-shielding losses with respect to the duct:

dB q_st > 0 (D.3.3a)

dB otherwise (D.3.3b)

dB q_sr > 0 (D.3.4a)

dB otherwise (D.3.4b)

D.4 Over-sea surface duct coupling corrections

Obtain the distance from each terminal to the sea in the direction of the other terminal:

d_ct = coast distance from transmitter km (D.4.1a)

d_cr = coast distance from receiver km (D.4.1b)

As for d_tm and d_lm in § D.1 above, it is preferable to obtain the distances over land to the first coast from the IDWM. If climatic zone codes are inserted into z_i as described in § 2.1, d_ct and d_cr should be calculated on the assumption that when adjacent values of z_i differ, the change occurs half-way between the corresponding profile points.

The over-sea surface duct coupling corrections for the transmitter and receiver, A_ct and A_cr respectively, are both zero except for the following combinations of conditions:

dB

if (w ³ 0.75) and (d_ct ≤ d_lt) and (d_ct ≤ 5 km) (D.4.2a)

dB otherwise (D.4.2b)

dB

if (w ³ 0.75) and (d_cr ≤ d_lr) and (d_cr ≤ 5 km) (D.4.3a)

dB otherwise (D.4.3b)

where w is the fraction of the path over sea as given in Table 3.1.

D.5 Total coupling loss to the anomalous propagation mechanism

The total coupling losses between the antennas and the anomalous propagation mechanism can now be calculated as:

dB (D.5.1)

A_lf is an empirical correction to account for the increasing attenuation with wavelength in ducted propagation:

dB if f < 0.5 GHz (D.5.2a)

dB otherwise (D.5.2b)

where w is the fraction of the path over sea as given in Table 3.1.

D.6 Angular-distance dependent loss

Specific angular attenuation within the anomalous propagation mechanism:

dB/mrad (D.6.1)

Adjusted transmitter and receiver horizon elevation angles:

mrad (D.6.2a)

mrad (D.6.2b)

Adjusted total path angular-distance:

mrad (D.6.3)

Angular-distance dependent loss:

dB (D.6.4)