Source code for irfpy.cena.backscatter_angle

''' Module to implement the backscatter angle.
'''
import os
import sys
import logging
import datetime
import math

import numpy as np

def _torad(deg):
    return deg * np.pi / 180.


[docs]def fs(sza, phi, theta):
    ''' Equation (2)

    :param sza: Solar zenith angle in degrees.
    :param phi: Phi angle in degrees.
    :param theta: Theta angle in degrees.
    '''

    return f0(sza, phi, theta) * f1(sza, phi, theta) * f2(sza, phi, theta) * f3(sza, phi, theta)

[docs]def f0(sza, phi, theta):
    ''' Equation (3)a

    :param sza: Solar zenith angle in degrees.
    :param phi: Phi angle in degrees.
    :param theta: Theta angle in degrees.
    '''
    return 0.009 * z0(sza)

[docs]def f1(sza, phi, theta):
    ''' Equation (3)b

    :param sza: Solar zenith angle in degrees.
    :param phi: Phi angle in degrees.
    :param theta: Theta angle in degrees.
    '''
    return _torad(z1(sza)) * np.cos(2 * _torad(phi)) + (1 - _torad(z1(sza)))

[docs]def f2(sza, phi, theta):
    ''' Equation (3)c

    :param sza: Solar zenith angle in degrees.
    :param phi: Phi angle in degrees.
    :param theta: Theta angle in degrees.
    '''
    return z2(sza) * np.cos(_torad(phi)) + (1-z2(sza))

[docs]def f3(sza, phi, theta):
    ''' Equation (3)d

    :param sza: Solar zenith angle in degrees.
    :param phi: Phi angle in degrees.
    :param theta: Theta angle in degrees.
    '''
    return (1 - z3(sza) / 90.0) * np.sin(_torad(theta) + _torad(z3(sza))) + z3(sza) / 90.0

[docs]def z0(sza):
    ''' Equation (5)a

    :param sza: Solar zenith angle in degrees.
    '''

    return 1.24 * np.cos(_torad(1.44 * sza - 48.7))

[docs]def z1(sza):
    ''' Equation (5)b

    :param sza: Solar zenith angle in degrees.
    '''
    return 0.30 * sza + 1.72

[docs]def z2(sza):
    ''' Equation (5)c

    :param sza: Solar zenith angle in degrees.
    '''

    return 0.24 * np.cos(_torad(74.48 - 1.52 * sza))

[docs]def z3(sza):
    ''' Equation (5)d

    :param sza: Solar zenith angle in degrees.
    '''
    return 90 - 1.03 * sza