REFF versus phase angle in 633 nm of all samples. The incident light has an azimuth angle of 0° and a zenith angle of 40° The positive and negative phase angles indicate the azimuth angle is within [0°, 180°] and [180°, 360°], respectively. The plots look asymmetrical for the positive and negative phase angle regions because there are more measurement data points in the positive phase angle region, where the relative azimuth angle is between [0°, 180°].