def _get_azimuth_correction(self, coe, azimuth):
        """
        This is the azimuth correction defined in the functional form (see
        equation 3 at page 2256)
        """
        term1 = abs(np.cos(np.radians(2.*azimuth)))
        term2 = abs(np.sin(np.radians(2.*azimuth)))*coe['a5']
        return np.log(np.max(np.hstack((term1, term2))))