Retrievals of cloud fraction and cloud albedo from surfacebased shortwave radiation measurements: A comparison of 16year measurements

Ground-based radiation measurements have been widely conducted to gain information on clouds and the surface radiation budget. To examine the existing techniques of cloud property retrieval and explore the underlying reasons for uncertainties, a newly developed approach that allows for simultaneous retrievals of cloud fraction and cloud albedo from ground-based shortwave broadband radiation measurements, XL2013, is used to derive cloud fraction and cloud albedo from ground-based shortwave broadband radiation measurements at the Department of Energy Atmospheric Radiation Measurement Southern Great Plains site. The new results are compared with the separate retrieval of cloud fraction and cloud albedo using Long2006 and Liu2011, respectively. The retrievals from the broadband radiation measurements are further compared with those based on shortwave spectral measurements (Min2008). The comparison shows overall good agreement between the retrievals of both cloud fraction and cloud albedo, with noted differences, however. The Long2006 and Min2008 cloud fractions are greater on average than the XL2013 values. Compared to Min2008 and Liu2011, the XL2013 cloud albedo tends to be greater for thin clouds but smaller for thick clouds, with the differences decreasing with increasing cloud fraction; the neglect of land surface albedo and cloud absorption by Liu2011 also contributes the difference in cloud albedo. Further analysis reveals that the approaches that retrieve cloud fraction and cloud albedo separately may suffer from mutual contamination of errors in retrieved cloud fraction and cloud albedo.