MODIS/Terra Vegetation Indices 16-Day L3 Global 250m SIN Grid V006

The MOD13Q1 Version 6 data product was decommissioned on July 31, 2023. Users are encouraged to use the [MOD13Q1 Version 6.1](https://doi.org/10.5067/MODIS/MOD13Q1.061) data product.

The Terra Moderate Resolution Imaging Spectroradiometer (MODIS) Vegetation Indices (MOD13Q1) Version 6 data are generated every 16 days at 250 meter (m) spatial resolution as a Level 3 product. The MOD13Q1 product provides 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 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.

Along with the vegetation layers and the two quality layers, the HDF file will have MODIS 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 MOD09 surface reflectance products may have [impacted](https://landweb.modaps.eosdis.nasa.gov/displayissue?id=86) MOD13 Vegetation Index data products particularly over arid bright surfaces.
* [Corrections](https://landweb.modaps.eosdis.nasa.gov/data/userguide/LSRHighAerosolFlagFinal.pdf) were implemented in Collection 6.1 reprocessing.
* For complete information about known issues please refer to the [MODIS/VIIRS Land Quality Assessment website](https://landweb.modaps.eosdis.nasa.gov/knownissue?sensor=MODIS&sat=Terra&as=6).