Research on polarization characteristics of reflected radiation on Dunhuang radiometric calibration site

Reflected radiation measurement(such as surface reflectance, surface radiance, etc.)from the radiometric calibration site is very important for the vicarious calibration of satellite sensors. Measurement error can be caused by the polarization effect of the reflected radiation from the radiometric calibration site, because of the fact that field instruments possess a certain degree of polarization sensitivity. A non-fixed-point measurement method based on multi-band polarization imager and tower crane and a fixed-point measurement method based on spectropolarimeter and bidirectional reflectance distribution function (BRDF) measurement frame were adopted to measure the multi-angular polarization distribution and local polarization homogeneity of the reflected radiation at the 490 nm and 670 nm bands in Dunhuang site. The results show that the reflected radiation from Dunhuang site possesses a certain degree of polarization characteristics. The polarization characteristics is wavelength-depended, the degree of polarization (DOP) of 490 nm band is obviously higher than 670 nm band, and the multi-angle polarization distribution is symmetric about the principle plane defined by the sun and instrument. In the principle plane, the DOP in forward scattering area (FSA) is higher than backward scattering area (BSA), and the DOP increased by the increasing of the view zenith angle (VZA). The angle distribution feature is fully consistent for the non-fixed-point method and fixed-point method. The local polarization homogeneity is about 6% for Φ100 m dimension area. The research on the polarization characteristics of reflected radiation from the calibration site is of great significance to the vicarious calibration scheme establishment and radiation measurement accuracy improvement.