The MODIS/Aqua Snow Cover Monthly L3 Global 0.05Deg CMG (MYD10CM) data set, new for Version 5 (V005), contains snow cover and Quality Assessment (QA) data in Hierarchical Data Format- Earth Observing System (HDF-EOS) format, and corresponding metadata. This data set consists of 7200 column by 3600 row global arrays of snow cover in a 0.05 deg Climate Modeling Grid (CMG). MODIS snow cover data are based on a snow mapping algorithm that employs a Normalized Difference Snow Index (NDSI) and other criteria tests. Monthly average snow cover is calculated from the daily global products for the month. Data are stored in HDF-EOS format, and are available from 04 July 2002 to present via FTP. Data can also be obtained in GeoTIFF format by ordering the data through the Data Pool.
Quality indicators for MODIS snow data can be found in the following places: AutomaticQualityFlag and the ScienceQualityFlag metadata objects and their corresponding explanations; AutomaticQualityFlagExplanation and ScienceQualityFlagExplanation located in the CoreMetadata.0 global attributes; Custom local attributes associated with each Scientific Data Set, for example, Snow Cover; and the Snow ... Spatial QA field. These quality indicators are generated during production or in post-production scientific and quality checks of the data product. The AutomaticQualityFlag is automatically set according to conditions for meeting data criteria in the snow mapping algorithm. In most cases, the flag is set to either Passed or Suspect, and in rare instances it may be set to Failed. Suspect means that a significant percentage of the data were anomalous and that further analysis should be done to determine the source of anomalies. The AutomaticQualityFlagExplanation contains a brief message explaining the reason for the setting of the AutomaticQualityFlag. The ScienceQualityFlag and the ScienceQualityFlagExplanation are set after production, either after an automated QA program is run or after the data product is inspected by a qualified snow scientist. Content and explanation of this flag are dynamic so it should always be examined if present.