Comparison of MODIS Snow Albedo To Field Measurements In Central Greenland
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Spectral snow albedo, physical snow properties, and snow chemistry were measured daily during May, June, and July 2011 at Summit, Greenland to investigate the variability in snow albedo and its impact on aerosol direct radiative forcing. In this study we compare our spectral albedo measurements to the Moderate Resolution Imaging Spectrometer (MODIS) daily albedo product. We additionally compare to albedo measurements from the Baseline Surface Radiation Network station at Summit (BSRN), and to modeled albedo using measured snow physical and chemical properties as input to the DISORT code. The spectral albedo measurements were made with an Analytical Spectral Devices (ASD) spectroradiometer at 350 – 2200 nm. We calculate weighted integrals of the spectral data to compare to seven MODIS narrow bandwidths ranging the UV through Infrared, as well as a broadband product that represents the full solar spectrum. Root mean square error (RMSE) for MODIS and field-measured albedo is 0.033 (mean difference of 0.023) for the broadband integration using MODIS high-quality only retrievals, and the narrow bandwidths range 0.022 – 0.077 RMSE (0.009 – 0.063 mean difference). The broadband values show an improvement in error from previous MODIS field validation studies, particularly in the UV and visible wavelengths. MODIS is consistently lower in magnitude than the field measured albedo, and shows poor correlation. The daily and multiday range of variability of the field measurements is much greater than MODIS albedo, and evidence is presented in support of the field-measured daily variability. Spatial variability is also constrained with data from multiple spatial surveys, and it is shown that surface roughness and error due to apparent albedo likely has a dominating effect on spatial variability, whereas the greater range of daily variability is dominated by changes in snow surface properties.