2 November 2015
The Areal Averaged Albedo (AREALAVEALB) value-added product yields areal averaged surface spectral albedo estimates from multifilter rotating shadowband radiometer (MFRSR) measurements collected under fully overcast conditions via a simple one-line equation (Barnard et al. 2008), which links cloud optical depth, normalized cloud transmittance, asymmetry parameter, and areal averaged surface albedo under fully overcast conditions. The corresponding algorithm has been initially evaluated for multiyear MFRSR data collected at the Southern Great Plains (SGP; Kassianov et al. 2014) and Eastern North Atlantic (ENA; Kassianov et al. 2017).
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Traditionally, combined sets of tower-based downward- and upward-looking instruments are used for measuring the surface albedo. The tower measurements observe the albedo over a very small area and can be considered local measurements. However, the measured local albedo may not be representative of a larger area-averaged surface albedo that encompasses an inhomogeneous surface with many different local albedos. Because most radiative transfer calculations require an area-averaged albedo, the use of a local albedo may be responsible for large uncertainties in these calculations. Moreover, the tower-based measurements of surface albedo are limited to the SGP, ENA, and North Slope of Alaska observatories, and an ARM Mobile Facility (AMF) deployment at Cape Cod, Massachusetts.
In contrast to these well-established sites, AMFs have been deployed in many locations around the world. The AMFs have a suite of instruments for measuring solar radiation at the surface, including the MFRSR. The MFRSR measurements have been used extensively for retrieving optical and microphysical properties of clouds, such as cloud optical depth. However, downward-looking spectral measurements are unavailable at most AMF deployments, and even when available, these only provide the capacity to measure local albedos.
References
Barnard JC, CN Long, EI Kassianov, SA McFarlane, JM Comstock, M Freer, and GM McFarquhar. 2008. “Development and evaluation of a simple algorithm to find cloud optical depth with emphasis on thin ice clouds.” The Open Atmospheric Science Journal, 2, doi:10.2174/1874282300802010046.
Kassianov E, J Barnard, C Flynn, L Riihimaki, J Michalsky, and G Hodges. 2014. “Areal-Averaged Spectral Surface Albedo from Ground-Based Transmission Data Alone: Toward an Operational Retrieval.” Atmosphere, 5(3), doi:10.3390/atmos5030597.
Kassianov E, J Barnard, C Flynn, L Riihimaki, L Berg, and D Rutan. 2017. “Areal-Averaged Spectral Surface Albedo in an Atlantic Coastal Area: Estimation from Ground-Based Transmission.” Atmosphere, 8(7), 123, doi:10.3390/atmos8070123.