Shadow Has Little Effect on the Spectral Response of Urban Surface Polarized Reflectance

It is difficult to form a quantitative remote-sensing model to describe the reflectance of shadowed urban surfaces. However, it is probably feasible to describe the spectral response of surface polarized reflectance (SPR). In this letter, we clarify the role of shadow in the spectral response of urban SPR from in situ and airborne measurements, which were obtained in Hefei and Binhai New Area, China, respectively. The in situ SPR of concrete and asphalt surfaces, as two largest coverage types of urban surface, shows a decreasing linear trend with the shadow proportion. The ratios between SPR at different wavelengths are around 1. The airborne SPRs are determined using bright, mixed (containing bright areas and shadows), and total (bright and mixed) pixels, which show similar spectral responses: the regression lines of 555 versus 865 nm and 670 versus 865 nm are close to the y = x line, their correlation coefficients are around 0.9, and coefficients of variation are less than 0.3. These results proved that the shadow has little effect on spectral responses of urban SPR, which can be used in quantitative remote sensing of atmosphere over urban areas.