Surface Albedo (CLARA-A2) from EUMETSAT CM-SAF
Topics
- Access
- Description
- Parameters
- Coverage, spatial and temporal resolution
- Data quality
- Contact person
- References
- Data citation
Access
RESTRICTED: This link to the data set is only available for a restricted user group. The data set is only accessible in CEN/MPI net or accessible from external nets with a customer account. Please contact ICDC if you would like to access this data from outside the network.
- View surface albedo data at LAS
- Access surface albedo data via OPeNDAP
- Data access via file system: /data/icdc/land/eumetsat_clara2_surfacealbedo/
Description
CLARA-A2 stands for "CM SAF cLouds, Albedo RAdiation data record, AVHRR-based, Edition 2" and comprises a suite of radiation and cloud parameters derived within the EUMETSAT Climate Monitoring Satellite Application Facility (CM-SAF) from Advanced Very High Resolution Radiometer (AVHRR) data.
Here we offer (for internal use only) and briefly describe the surface albedo product. Products are also available at ICDC for radiation and clouds.
Data from AVHRR channels 1 and 2 are used to compute the top-of-atmosphere (TOA) reflectances and apply the required cloud masking by utilizing the AVHRR-PPS package (see Dybbroe et al., 2005 in references). Depending on surface type: water, ice, land (snow-covered, bare, different vegetation zones) different processing steps are carried out. Various data sets are used to carry out the required atmospheric correction (e.g. for aerosol optical depth: TOMS and/or OMI data; for surface wind speed over water: SMMR through SSMIS data; for other parameters: ERA-Interim atmospheric re-analysis data). Over land also topographic corrections are applied. Details about the processing steps can be found in the respective ATBD as well as in the papers by Jin et al. (2011), Xiong et al. (2002), and Liang (2000) in thereferences.
We offer version 2.1 of edition 2 of the CLARA data set, i.e. CLARA-A2, for internal use only. Version 2.1 includes version 2.0 which terminates end of 2015.
Last update of data set at ICDC: December 3 2020.
Parameters
| Name | Unit |
|---|---|
| Mean broadband shortwave (0.25 … 2.5µm) surface albedo (black sky albedo) | % |
| Median broadband shortwave (0.25 … 2.5µm) surface albedo (black sky albedo) | % |
| standard deviation of the mean broadband shortwave surface albedo | % |
| 3rd statistical moment: skewness of the mean broadband shortwave surface albedo | % |
| 4th statistical moment: kurtosis of the mean broadband shortwave surface albedo | % |
| Mean sun zenith angle for valid albedo values | degree |
| standard deviation of the mean sun zenith angle for valid albedo values | degree |
| Number of valid albedo values per grid cell | - |
Coverage, spatial and temporal resolution
Period and temporal resolution:
- 1982-01 to 2019-06
- Monthly
Coverage and spatial resolution:
- Global
- Spatial resolution: 0.25 degrees x 0.25 degrees, equally spaced lat/lon grid (Climate Modeling Grid, CMG)
- Geographic longitude:-179.875°E to 179.875°E
- Geographic latitude: -89.875°N to 89.875°N
- Dimension: 1440 columns x 720 rows
- Altitude: following terrain
Format:
- NetCDF
Data quality
The data set does not include separate uncertainty estimates. It does contain, however, information about the standard deviation per grid cell which could be taken as a measure of uncertainty. It contains also information about solar zenith angle and the number N of valid albedo values used to compute the statistical moments. It is recommended to use only data with N larger than 20.
Because a few of the additional data required for the processing (see description) are missing in 2015, it is recommended to not over-interpret results that seem to be specific for that particular year.
Evaluation of the product confirms that the target accuracy of 25% difference relative to the in-situ observation is met for nearly all sites used for the evaluation within the period 1992-2014. Mean absolute differences to surface albedo from evaluation data sets are often below 5%.
Browsing through the data set reveals that areas of a highly variable aerosol load, i.e. aerosol optical depth (AOD) and/or frequent cloud cover, can have artificially large surface albedo values. South China and Indonesia are candidates here.
Limitations and artifacts may also originate from extremely clear atmospheres (Antarctic interior), mixed cloud / snow covers, and land cover classifications not representing the actual conditions.
For more information about the quality and limitations of the data set we refer to the CM-SAF Product User Guide (PUM) and the CM-SAF Validation report in the references.
Contact
Climate Monitoring Satellite Application Facility (CM-SAF)
www.cmsaf.eu
email: contact.cmsaf (at) dwd.deStefan Kern
ICDC / CEN / University of Hamburg
E-Mail: stefan.kern"AT"uni-hamburg.de
References
Literature:
- Algorithm Theoretical Basis Document (ATBD) (pdf, not barrier free)
- Product User Manual (PUM) (pdf, not barrier free)
- Validation Report (pdf, not barrier free)
- Dybbroe, A., et al, 2005, SAFNWC AVHRR cloud detection and analysis using dynamics thresholds and radiative transfer modelling part I: Algorithm description. Journal of Applied Meteorology, 44, 39-54.
- Jin, Z., et al., 2004, A parameterization of ocean surface albedo. Geophysical Research Letters, 31, 22301.
- Jin, Z., et al., 2011, A new parameterization of spectral and broadband ocean surface albedo. Optics Express, 19(27), 26,429-26,443.
- Liang, S., 2000, Narrowband to broadband conversions of land surface albedo: Algorithms. Remote Sensing of Environment, 76, 213-238.
- Xiong, X., et al., 2002, Surface albedo over the Arctic Ocean derived from AVHRR and its validation with SHEBA data. Journal of Applied Meteorology, 41, 413-425.
Websites:
Data citation
Please cite the data as follows:
Karlsson, Karl-Göran; Anttila, Kati; Trentmann, Jörg; Stengel, Martin; Solodovnik, Irina; Meirink, Jan Fokke; Devasthale, Abhay; Kothe, Steffen; Jääskeläinen, Emmihenna; Sedlar, Joseph; Benas, Nikos; van Zadelhoff, Gerd-Jan; Stein, Diana; Finkensieper, Stephan; Håkansson, Nina; Hollmann, Rainer; Kaiser, Johannes; Werscheck, Martin (2020): CLARA-A2.1: CM SAF cLoud, Albedo and surface RAdiation dataset from AVHRR data - Edition 2.1, Satellite Application Facility on Climate Monitoring, DOI:10.5676/EUM_SAF_CM/CLARA_AVHRR/V002_01, https://doi.org/10.5676/EUM_SAF_CM/CLARA_AVHRR/V002_01 .
All intellectual property rights of the CM SAF products belong to EUMETSAT. The use of these products is granted to every interested user, free of charge. If you wish to use these products, EUMETSAT copyright credit must be shown by displaying the words "copyright (year) EUMETSAT" on each of the products used.
and with the following acknowledgments:
Thanks to ICDC, CEN, University of Hamburg for data support.