Polarized reflectances of urban areas: Analysis and models

Accurate BPDF (Bidirectional Polarization Distribution Functions) of urban will help to improve the accuracy of inverted aerosol parameters that is very important for the research of urban atmospheric pollution and climate change. With Fresnel formula of polarization as the foundation, this paper studies three important factors that influence the BPDF: shadow, slope distribution and NDVI, and proposes a new BPDF model (named as Xie-Cheng model for convenience in comparison) for urban areas. Because the influence of slope distribution is trivial, only two parameters are needed in the new model, one controlling the shadow and the other for overall scale. An experimental factor is introduced into the model to compensate the influence of NDVI for polarized reflectance more accurately. Experiments prove that new model performs best in both correlation and RMSE for measurements not only with different urban places around the world but also clustered urban data by different NDVIs. Compared with the best current BPDF model, new model can reduce the average RMSE error by about 4.5% for different urban areas. Error distribution in polar coordinates also shows that new model can achieve smallest errors in almost all directions under fixed sun zenith angle.