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 ZMAW net or via CliSAP login What does that mean?
Data of the Moderate Resolution Imaging Spectroradiometer (MODIS) were used to generate a global data set of the fractional snow cover over land for a so-called climate-modelling grid (CMG) with 0.05° degree grid cell size. This data set comprises the mean monthly snow cover for each grid cell together with a quality flag informing about the quality of the daily data used to generate this climatology (e.g. influence by clouds and number of adaequate observations).
The data set is based on global daily data on the same grid (3.), which are based on global data obtained on a 500 m grid (2.), which in turn are a result from an interpolation of the fractional snow cover derived for each single MODIS overpass (1.). The steps required for the product offered here are described in a number (unfortunately) of different documents which can be found in http://nsidc.org/data/modis/data_summaries/index.html#snow. The most important ones are:
In order to derive the snow cover data of MODIS channels 4 (0.55µm) and 6 (1.6µm) are used to calculate the Normalized Difference Snow Index (NDSI). This index is used in a regression to obtain the fractional snow cover. Influence of vegetation, solar illumination, and clouds are taken into account. More details can be found in the document listed above under 1. and the references listed below.
Coverage, spatial and temporal resolution
Period and temporal resolution:
(08/2000, 06/2001, 03/2002, and 12/2003 are missing)
(April 8 is missing)
Coverage and spatial resolution:
The data set contains quality flags.
For the monthly data set these are relatively simple and only mark pixels where no snow cover values are available or where these are at least doubtful due to i) clouds, ii) missing daylight, iii) open water, or iv) an ambiguous classification.
The daily product contains more information. On the one hand there is one additional data layer giving the percentage cloud fraction. On the other hand there is another additional data layer giving a confidence interval ranging from 0 (bad) to 100 (perfect). Similar to the monthly product there is a fourth data layer specifying areas ii) to iv) (see above) plus areas of lake ice.
Note: When using the daily product it is MANDATORY to COMBINE the information of the snow cover AND cloud cover data layers! A completely snow-covered, clear-sky MODIS pixel gives a snow fraction of 100%. The same pixel covered partially by clouds, e.g. 30%, gives a snow fraction of 70%.
NSIDC User Services
Please cite usage of this data as follows:
Hall, D. K., G. A. Riggs, and V. V. Salomonson. 2006, updated monthly. MODIS/TERRA Snow Cover Monthly L3 Global 0.05Deg CMG V005, [list the dates of the data used], Boulder, CO, National Snow and Ice Data Center. Digital Media, distributed in netCDF format by the Integrated Climate Data Center (ICDC, http://icdc.zmaw.de University of Hamburg, Hamburg, Germany).