Source code for itmlogic.los_attenuation.alos

import math
import numpy as np

def alos(d, prop):
    """
    Find the 'line-of-sight attenuation' at the distance d using a combination of plane
    earth fields and directed fields (Eqn 4.44 of "The ITS Irregular Terrain Model,
    version 1.2.2: The Algorithm"). A call with d = 0 sets up initial constants.

    Parameters
    ----------
    d : float
        Distance in meters.
    prop : dict
        Contains all input propagation parameters

    Returns
    -------
    alos : float
        The estimated line-of-sight attenuation.

    """
    q = (1 - 0.8 * math.exp(-d / 50e3)) * prop['dh']

    s = 0.78 * q * math.exp(-(q / 16)**0.25)

    q = prop['he'][0] + prop['he'][1]

    sps = q / math.sqrt(d**2 + q**2)

    r = (
        (sps - prop['zgnd']) /
        (sps + prop['zgnd']) *
        math.exp(-min(10, prop['wn'] * s * sps))
        )

    q = abs(r)**2

    if q < 0.25 or q < sps:
        r = r * math.sqrt(sps / q)

    alos1  = prop['emd'] * d + prop['aed']

    q = prop['wn'] * prop['he'][0] * prop['he'][1] * 2 / d

    if q > 1.57:
        q = 3.14 - 2.4649 / q

    alos1 = (
        (-4.343 *
        np.log(abs(complex(math.cos(q),-math.sin(q)) + r)**2)- alos1) *
        prop['wis'] + alos1
        )

    return alos1