Source code for itmlogic.diffraction_attenuation.fht

import math
import numpy as np

def fht(x,pk):
    """
    Supporting function for the height gain in the "three radii method" used in the
    computation of diffractive attenuation, as described in equations (4.20) and (6.2)-(6.7)
    of "The ITS Irregular Terrain Model, version 1.2.2: The Algorithm" with inputs
    corresponding to the "x" and "K" parameters of these equations.

    Parameters
    ----------
    x : float
        x parameter specified in equations (4.20) and (6.2)-(6.7) of "The ITS Irregular
        Terrain Model, version 1.2.2: The Algorithm"
    pk : float
        k parameter specified in equations (4.20) and (6.2)-(6.7) of "The ITS Irregular
        Terrain Model, version 1.2.2: The Algorithm"

    Returns
    -------
    fht1 : float
        Estimated diffractive attenuation.

    """
    if x < 200:
        w = -np.log(pk)

        if pk < 1e-5 or (x*w**3) > 5495:
            fht1 = -117
            if x > 1:
                fht1 = 17.372 * np.log(x) + fht1

        else:
            fht1 = 2.5e-5 * x**2 / pk - 8.686 * w - 15

    else:
        fht1 = 0.05751 * x - 4.343 * np.log(x)

        if x < 2000:
            w = 0.0134 * x * math.exp(-0.005 * x)
            fht1 = (1 - w) * fht1 + w * (17.372 * np.log(x) - 117)

    return fht1