PNNL

Abstract

The aerosol optical depth (AOD) is an important parameter for describing the Earth’s radiation budget and hydrologic cycle and it is critical in the context of the cloud-aerosol-precipitation problem. The extracting AOD from satellite-measured cloudy-sky reflectances represents a great challenge in remote sensing studies, where cloud-induced artifacts can be responsible for large uncertainties (up to 140%) in the satellite-derived AOD. We have developed a new method, named the reflectance ratio (RR) method, which presents an effective way to reduce substantially the impact of the cloud contamination on the retrieved AOD. The RR method relies on the well-established fact that clouds reflect about the same amount of sunlight regardless of the wavelength, and thus the reflectance ratio is less sensitive to the radiative effects of clouds than reflectance. For partly cloudy conditions, we examined performance of the RR method using a case study and demonstrated that the RR method has an opportunity to obtain accurate (~5%) and reasonable (~15-30%) estimations of domain-averaged AOD between clouds at 660-nm wavelength and 470-, 870-nm wavelengths, respectively .