Linear polarization measurements of a wheat canopy

The amount of linearly polarized light reflected by a wheat canopy was measured using a polarizing filter attached to a radiometer at two wavelengths (478 nm and 668 nm) and three view zenith angles (60°, 70°, 80°). Measurements were carried out in the anti-solar direction in the principal plane, with relative azimuth between Sun and view directions being 180°. It is found that the degree of polarization (DOP) and mean polarized radiance (R¯ Q ) between stages is statistically significant at view zenith angles of 70° and 80°, in the blue wavelength region. It is concluded that DOP and R¯ Q are better indicators of the onset of heading stage. Calculations of polarized reflectance using Fresnel reflection equations are also presented.