This data set is only available for a restricted user group, please contact us if you want to access these data.
Coverage, spatial and temporal resolution
Period and temporal resolution:
- 1982-01 to 2015-12
- Monthly (daily data on request)
Coverage and spatial resolution:
- 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
Some of the offered products come with a retrieval uncertainty estimate, some others don't; all are provided, however, at least with a standard deviation of the mean which can serve an estimate of the uncertainty. The best sources to learn about the uncertainties and results of the validation are the CM-SAF Product User Guide (e.g. Table 6.1) and the CM-SAF Validation Report as well as the references.
In the following we briefly summarize a few of the limitations:
- For cloud fraction(s): Limitations arise for optically thin clouds (optical thickness < 0.15), and ice clouds over cold ground surfaces --> clouds may be missed; considerable underestimation arise during polar winter and under twilight conditions; false cloud may occur in areas of challenging surface emissivities, e.g. night-time desert.
- For cloud top parameters: In case of strong temperature inversions cloud top estimates become unreliable, this applies in general but in particular to polar regions and also to boundary layer clouds where cloud tops might be biased high by up to 1000m; problematic are optically very thin and/or multi-layered clouds as well as clouds being interpreted as opaque but are in fact diffuse and/or multi-layered in which case an under-estimation of the cloud top by up to 2000 m is possible
- For cloud physical properties like cloud phase, liquid and ice water path as well as optical thickness and effective particle radius difficulties arise in areas of high surface reflectances (ice & snow) and for highly 3-dimensional and/or broken cloud covers; the ice crystal shape used might not well represent the actual ice crystal shape distribution and hence effective ice particle size and cloud ice water paths might be biased considerably more often than their liquid counterparts; the smaller the actual penetration depth into the clouds is the more the retrieved parameters represent the near-cloud top properties rather than the mid- or low-level ones; the sensitivity to solar zenith angle (SZA) is quite high so that it is recommended to not use such data for SZA > 65°.
Climate Monitoring Satellite Application Facility (CM-SAF)
Helpdesk at www.cmsaf.eu
email: contact.cmsaf (at) dwd.de
ICDC / CEN / University of Hamburg
email: stefan.kern (at) uni-hamburg.de
The citation for this data set is:
Karlsson, Karl-Göran; Anttila, Kati; Trentmann, Jörg; Stengel, Martin; Meirink, Jan Fokke; Devasthale, Abhay; Hanschmann, Timo; Kothe, Steffen; Jääskeläinen, Emmihenna; Sedlar, Joseph; Benas, Nikos; van Zadelhoff, Gerd-Jan; Schlundt, Cornelia; Stein, Diana; Finkensieper, Stephan; Håkansson, Nina; Hollmann, Rainer; Fuchs, Petra; Werscheck, Martin (2017): CLARA-A2: CM SAF cLoud, Albedo and surface RAdiation dataset from AVHRR data - Edition 2, Satellite Application Facility on Climate Monitoring, DOI:10.5676/EUM_SAF_CM/CLARA_AVHRR/V002, https://doi.org/10.5676/EUM_SAF_CM/CLARA_AVHRR/V002.
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.