AREALAVEALB

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arealavealb > Areal Averaged Spectral Surface AlbedoVAP Type(s) > Evaluation

The Areal Averaged Albedo VAP yields areal averaged surface spectral albedo estimates from 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 multi-year MFRSR data collected at ARM SGP site (Kassianov et al. 2014).

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 SGP and NSA sites, and the TCAP AMF deployment.

In contrast to these well-established sites, the ARM Mobile Facilities (AMFs) have been deployed for many locations around the world. The AMFs have a suite of instruments for measuring solar radiation at surface, including the Multi-Filter Rotating Shadowband Radiometer (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.

Purpose

Spectral surface albedo measurements are needed for radiative transfer calculations and retrievals of aerosol and cloud optical depths. This algorithm produces an areal average albedo at mfrsr wavelengths which is likely more representative of the region of interest for radiative transfer calculations than the directly measured albedo from tower and surface measurements. Additionally, tower measurements are only available at a few sites, and usually not AMF sites, impeding our ability to calculate albedo.

Measurements

Locations

  • Fixed
  • AMF1
  • AMF2
  • AMF3

Data Details

Developed By Laura Riihimaki | Evgueni Kassianov
Contact Laura Riihimaki
Resource(s) Data Directory
ReadMe
Data format netcdf
Site SGP
Content time range 4 March 2019 - 5 March 2019
Attribute accuracy No formal attribute accuracy tests were conducted
Positional accuracy No formal positional accuracy tests were conducted
Data Consistency and Completeness The algorithm is not valid for days with snow on the ground or insufficient overcast skies. These days were screened out of the data using a surface albedo threshold and cloud fraction measurements respectively.
Access Restriction No access constraints are associated with this data.
Use Restriction No use constraints are associated with this data.
File naming convention follows ARM data standards
Citations Kassianov E, Barnard J, Flynn C, Riihimaki L, Michalsky J, Hodges G. Areal-Averaged Spectral Surface Albedo from Ground-Based Transmission Data Alone: Toward an Operational Retrieval. Atmosphere. 2014; 5(3):597-621, doi:10.3390/atmos5030597.

Barnard J.C., C.N. Long, E.I. Kassianov, S.A. McFarlane, J.M. Comstock, M. Freer, and G. Farquhar. 2008: Development and Evaluation of a Simple Algorithm to Find Cloud Optical Depth with Emphasis on Thin Ice Clouds, Open Atmospheric Science Journal, 2, 46-55. doi:10.2174/1874282300802010046.