MODIS/Aqua Sea Ice Extent 5-Min L2 Swath 1km (MYD29) contains the following fields: sea ice by reflectance, sea ice by reflectance pixel quality assurance (QA), ice surface temperature (IST), IST pixel QA, sea ice by IST, combined sea ice, latitudes, and longitudes in HDF-EOS format along with corresponding metadata. Latitude and longitude geolocation fields are at 5 km resolution while all other ... fields are at 1 km resolution. Version 4 (V004) MYD29 data, the most current version available, uses Aqua/MODIS band seven instead of band six. The sea ice algorithm uses a Normalized Difference Snow Index (NDSI) modified for sea ice to distinguish sea ice from open ocean based on reflective and thermal characteristics. The only data available for Version 4 (V004) is the Golden Month, which is a sample of V004 data covering the time period 29 August 2002 (day of year 241) through 7 October 2002 (day of year 280). The Golden Month is only available by special request by contacting NSIDC User Services. Please note that NSIDC now has a complete series of Version 5 data, which is the highest version number now available and represents the best quality of data.
In MYD29 Version 4 (V004) data, the sea ice algorithm uses Aqua/MODIS band 7. Good quality has been observed in the sea ice maps; however, investigation of effects of the switch to band 7 is continuing. The cloud mask product, MYD35_L2, used as input to the MYD29 algorithm also changed to use of band 7. The effect of that change relative to sea ice/cloud discrimination is being investigated. The ... IST was not affected by the switch to band 7 except, possibly indirectly by the cloud mask switch to band 7. Validation status is set at provisional until further validation work specific to Aqua IST maps can be completed. Provisional means that the products are partially validated; incremental improvements are still occurring. These are early science validated products and are useful for exploratory and process scientific studies. Quality may not be optimal since validation and quality assurance are ongoing. Users are urged to review product quality summaries before publication of results. Analysis of the quality of the sea ice data products is an ongoing activity. Specific information on the science quality of the sea ice data products is reported in the ScienceQualityFlagExplanation object in the CoreMetadata.0 global attribute. The URL for the quality assessment site is given in the product metadata and is linked to from the EOS Data Gateway (EDG) when ordering data. The ScienceQualityFlagExplanation is changed in response to analysis and should be checked for updated information. In the MOD29 and MOD29P1D data products there are two instances of the ScienceQualityFlagExplanation, one for sea ice determined by reflectance data and one for IST written in the metadata. Information on both is posted at that URL. The Ice Surface Temperature PixelQA and the Sea Ice by Reflectance PixelQA data fields provide additional information on algorithm results for each pixel within a spatial context, and are used as a measure of usefulness for sea ice data. QA data are stored as bit flags. QA information is extracted by reading the bits within a byte (See MODIS Sea Ice Quality Assurance Fields). The QA information tells if algorithm results were nominal, abnormal, or if other defined conditions were encountered for a pixel (Riggs, Hall, and Salomonson 2003). See MODIS Land Quality Assessment for further details.
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