This data set is only available for a restricted user group, please contact us if you want to access these data.
RESTRICTED only accessable in CEN/MPI net or via CliSAP login What does that mean?
Data of the Along Track Scanning Radiometer (ATSR) aboard the ERS-2 Satellite and the Advanced ATSR (AATSR) aboard the Envisat Satellite were used to obtain a data set of the percentage snow cover fraction on land with a grid resolution of 0.01°. First, grid cells containing clouds, open water and glaciers are masked out. Then two approaches (one for steep topography, one for all other areas) are combined to derive the snow cover fraction in per cent for each cloud free grid cell. For details of the approaches see the Product Guide.
The snow cover fraction can be derived with daily temporal resolution taking all satellite overpasses of a certain grid cell within one day into account. However, persistent cloud coverage can cause widespread and long-duration gaps in the data set of the daily snow cover fraction. Therefore we primarily offer the monthly aggregated snow cover fraction. For this data set all satellite overpasses of a certain grid cell within an entire calendar month are taken into account to calculate an average monthly snow cover fraction. More details can again be found in the Product Guide and on the GlobSnow web page: http:www.globsnow.info. In contrast to the first version we now offer data of the two sensors ATSR and AATSR separately; they overlap from 05/2002 to 06/2003.
This is version v2.1 of this product. Note that the update from v2.0 to v2.1 is not yet complete; AATSR based data for 2002 are still from v2.0. The update was required because a reprocessed AATSR L1b data set was released.
Last data update: December 11 2014.
|Snow cover||% (0 ... 100)|
|Standard deviation||% (0 ... 100)|
|Number of days with valid data||none|
Period and temporal resolution:
- ATSR: 06/1995 to 06/2003
- AATSR: 05/2002 to 04/2012
- Daily data for same time periods available on request
(01/1996 to 06/1996 are missing)
Coverage and spatial resolution:
- Northern Hemisphere
- Spatial resolution: 0.01° x 0.01°; cartesian grid
- Geographic longitude: -167.995°E to 191.995°E
- Geographic latitude: 25.005°N to 83.995°N
- Dimension: 36000 columns x 5900 rows
- Altitude: following terrain
For every grid cell the data set contains the standard deviation of the percentage snow cover fraction (basically a measure of the variability of the snow cover within the respective month and not a quality measure), a quality flag layer which gives information about why data gaps occur, and the number of days for which retrieval was possible. This latter data layer is NOT the number of days with snow cover.
The quality flags denote grid cells with clouds, to low sun angle, too dense vegetation but also grid cells where the retrieval did not converge, satellite data are missing or other reason inhibited a meaningful retrieval.
Evaluation results show that the ESA GlobSnow snow cover has an about 10% higher snow extent than the MODIS L2 snow cover product which is said to be caused by the better detection of snow in forested regions. A comparison with an even finer resolved snow cover product based on Landsat 7 ETM+ data indicated that the ESA GlobSnow snow cover underestimates the snow cover by 10%.
Highest potential for improvement would be a better cloud masking. Still grid cells with partial cloud cover (e.g. cloud rims) and grid cells with high and thus cold cloud tops are difficult to reliably classify as cloud covered. These can cause artefacts in the snow cover particularly during summer. For more information please take a look at the Product Guide.
ICDC / CEN / University of Hamburg
email: stefan.kern (at) uni-hamburg.de
Finish Meteorological Institute
email: kari.luojus (at) fmi.fi
Finish Meteorological Institute
email: jouni.pulliainen (at) fmi.fi
- GlobSnow V2 Product Guide
- GlobSnow Webpage: http://www.globsnow.info
- Metsämäki, S., et al., 2005, A feasible method for fractional snow cover mapping in boreal forest based on a reflectance model. Remote Sensing of Environment, 95(1), 77-95.
- Salminen, M., et al., 2009, The behavior of snow and snow-free surface reflectance in boreal forests: Implications to the performance of snow covered area monitoring. Remote Sensing of Environment, 113, 907-918.
- Metsämäki, S., et al., 2015, Introduction to GlobSnow Snow Extent products with considerations for accuracy assessment. Remote Sensing of Environment, 156(1), 96-108.
- GlobSnow-2 Newsletter no. 4, 2014-01