MODIS 8-day Snow Cover Extent - Curr vs Avg Period
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8-day Period
Pakistan
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Product Documentation
| The snow cover product from the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra 8-day L3 Global 500m Grid (MOD10A2) data set contains fields for maximum snow cover extent over an eight-day period and a chronology of snow occurrence observations. The MODIS snow cover data are based on a snow mapping algorithm that employs a Normalized Difference Snow Index (NDSI) and other criteria tests for determining snow classification. The algorithm identifies snow by its unique reflectance, absorption, and emittance properties. The MOD10A2 data consists of 1200 by 1200 kilometer gridded tiles in an integerized sinusoidal map projection. These data have been further transformed into geographic (latitude,longitude) coordinate space and have been mosaicked into regional summaries of maximum snow cover extent. The maps displayed here allow comparisons to the previous 8-day period, the previous year, and the average condition based on the 2001-2012 snow history. Standard snow cover accumulation/depletion curves relate the percent of a basin or zone that is covered by snow to elapsed time during the snow melt season. Such curves help provide an indication of the temporal and spatial extent of seasonal snow pack available for irrigation and municipal water use. A steep decrease in snow-covered area can be indicative of either shallow snow pack or high melt rates. On the other hand, a slow decrease results from either a deep snow cover or slow melt rates most likely due to low temperatures. Plotting snow cover versus degree days can help reduce this ambiguity, however these depletion curves measure the maximum extent of snow cover as a function of time without regard to air temperature. Using basin delineations derived from the 90m resampled HydroSHEDS (Hydrological data and maps based on SHuttle Elevation Derivatives at multiple Scales) digital elevation model (DEM), this analysis concentrated on watersheds upstream of important drainage areas. An elevation threshold of 2500 meters was applied to identify areas, within each basin, where snow extent equaled approximately 100 percent of the basin area when measured using the historical March average. Monthly averages (1966 - 2001) were taken from the National Snow and Ice Data Center (NSIDC) snow cover database at 25-kilometer resolution. The MODIS 8-day extent product, at 500-meter resolution, was used to make incremental measurements of snow cover extent above the 2500 meter zone for each basin. These data are presented for the current snow season, the previous two seasons, and an average calculated using the MODIS history beginning in 2001. References: NSIDC DAAC MODIS 8-day Snow Cover Extent Data Description http://nsidc.org/data/mod10a2.html NSIDC DAAC Northern Hemisphere EASE-Grid Data Description http://nsidc.org/data/nsidc-0046.html |
