The Vegetation Indices (VI)Quality data layer in the Version 6 MODIS VI data products(MxD13) currently show a discrepancy between VI Quality (MODLAND QA bits) and VI Usefulness bits for some pixels. 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.
Visit the MOD13 Known Issues site for a detailed example.
The MODIS VI data products are:
MODIS/Aqua Vegetation Indices 16-Day L3 Global 250m SIN Grid V006 - MYD13Q1
MODIS/Aqua Vegetation Indices 16-Day L3 Global 500m SIN Grid V006 - MYD13A1
MODIS/Aqua Vegetation Indices 16-Day L3 Global 1km SIN Grid V006 - MYD13A2
MODIS/Terra Vegetation Indices 16-Day L3 Global 250m SIN Grid V006 - MOD13Q1
MODIS/Terra Vegetation Indices 16-Day L3 Global 500m SIN Grid V006 - MOD13A1
MODIS/Terra Vegetation Indices 16-Day L3 Global 1km SIN Grid V006 - MOD13A2
Please contact LP DAAC User Services (lpdaac@usgs.gov)with any questions.