MODIS/Aqua Vegetation Indices 16-Day L3 Global 500m SIN Grid V006

The MYD13A1 Version 6 data product was decommissioned on July 31, 2023. Users are encouraged to use the MYD13A1 Version 6.1 data product.

The MYD13A1 Version 6 product provides Vegetation Index (VI) values at a per pixel basis at 500 meter (m) spatial resolution. There are two primary vegetation layers. The first is the Normalized Difference Vegetation Index (NDVI), which is referred to as the continuity index to the existing National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR) derived NDVI. The second vegetation layer is the Enhanced Vegetation Index (EVI), which has improved sensitivity over high biomass regions. The algorithm for this product chooses the best available pixel value from all the acquisitions from the 16 day period. The criteria used is low clouds, low view angle, and the highest NDVI/EVI value.

Provided along with the vegetation layers and two quality assurance (QA) layers are reflectance bands 1 (red), 2 (near-infrared), 3 (blue), and 7 (mid-infrared), as well as four observation layers.

Known Issues * The following issues have been detected:

* Unexpected missing data in the last cycles of each year.
* Incorrect instances of "NoData" and spikes in NDVI values.
* VI Usefulness Bits are not correctly assigned.

• For instances where the VI Quality (bits 0-1) is flagged as good and the VI Usefulness (bits 2-5) indicates the same pixels have the lowest usefulness score, users are advised to disregard the usefulness score.
• The incorrect representation of the aerosol quantities (low, average, high) in the Collection 6 MYD09 surface reflectance products may have impacted MYD13 Vegetation Index data products particularly over arid bright surfaces.
• Corrections were implemented in Collection 6.1 reprocessing.
• For complete information about known issues please refer to the MODIS/VIIRS Land Quality Assessment website.