Figure 470: SEAMCAT Interface to the ITU-R Rec. P.452-14 model

Table 83: ITU-R P.452-14 propagation model

Description	Symbol	Type	Unit	Comments
Variation	-	Boolean	-	Variation in path loss
Diffraction	-	Boolean	-	Select the diffraction component of the model
Tropospheric scatter	-	Boolean	-	Select the tropospheric scatter component of the model
Ducting/layer reflection	-	Boolean	-	Select the ducting/layer reflection component of the model
Water concentration	ρ	Scalar	g/m³	water vapour density for tropospheric study only
Surface pressure	P	Scalar	hPa	Surface pressure (default 1013.25 hPa)
Refraction index gradient	ΔN	Scalar	1/km	It is the average radio-refractive index lapse-rate through the lowest 1 km of the atmosphere, provides the data upon which the appropriate effective Earth radius can be calculated. Note that ΔN is a positive quantity.
Surface temperature	T	Scalar	Degree Celsius	Surface temperature (default 15 degree Celsius)
Latitude	φ_t, φ_r	Scalar	Degree	Latitude of station, used in the path centre location calculation
Additional clutter loss at the Tx	A_ht	Scalar	dB	Additional clutter loss at the Tx
Additional clutter loss at the Rx	A_hr	Scalar	dB	Additional clutter loss at the Rx
Antenna gain at the Tx	G_t	Scalar	dB	Antenna gain of the Tx in the direction of the horizon along the great-circle interference path (dBi)
Antenna gain at the Rx	G_r	Scalar	dB	Antenna gain of the Rx in the direction of the horizon along the great-circle interference path (dBi)
Sea level surface refractivity	N₀	Scalar	-	The sea-level surface refractivity, is used only by the troposcatter model as a measure of location variability of the troposcatter scatter mechanism. As the scatter path calculation is based on a path geometry determined by annual or worst-month values of ΔN, there is no additional need for worst-month values of N₀. The correct values of ΔN and N₀ are given by the path-centre values as derived from the appropriate maps.
Time Percentage		Distribution	%	Percentage time variability for which the calculated basic transmission loss is not exceeded

The longitude parameter of the Recommendation ITU-R P.452-14 is used for the computation of the position based on a grid point data file. In SEAMCAT, this parameter is not used as x and y coordinates are sufficient. The latitude, however is used in SEAMCAT in evaluation of the point incidence of anomalous propagation, β0 (%), for the path centre location where β0 (%) is the time percentage for which refractive index lapse-rates exceeding 100 N units/km can be expected in the first 100 m of the lower atmosphere. β0 (%) is used to estimate the relative incidence of fully developed anomalous propagation at the latitude under consideration.

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