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V005 MODIS Monthly Vegetation Indices 1km QA Science Data Sets
The QA information below is excerpted from the Quality Science Data Set within an HDF-EOS MYD13A3 file. Additional information may be available in the MODIS Aqua Vegetation Indices file specifications available on-line at
ftp://modular.nascom.nasa.gov/pub/LatestFilespecs/collection5/.
A summary Quality layer has been included in the MYD13A3: “pixel reliability.” This layer contains ranked values describing overall pixel quality (Table 1 below).
Because evaluation of V004 data collections revealed insignificant differences between the Quality assignments for NDVI versus EVI, the V005 MYD13 products include a single Quality layer pertinent to both indices (Table 2 below), rather than one layer for each. This reduces data volume as well as user confusion with multiple Quality layers.
TABLE 1: MYD13A3 Pixel Reliability
| Rank Key | Summary QA | Description |
|---|---|---|
| -1 | Fill/No Data | Not Processed |
| 0 | Good Data | Use with confidence |
| 1 | Marginal data | Useful, but look at other QA information |
| 2 | Snow/Ice | Target covered with snow/ice |
| 3 | Cloudy | Target not visible, covered with cloud |
TABLE 2: MYD13A3 VI Quality
| Bit 0 is the least significant (read bit words right to left) | |||
| bit | Long Name | Value | Key |
|---|---|---|---|
| 0-1 | MODLAND_QA | 00 | VI produced, good quality |
| 01 | VI produced, but check other QA | ||
| 10 | Pixel produced, but most probably cloudy | ||
| 11 | Pixel not produced due to other reasons than clouds | ||
| 2-5 | VI usefulness | 0000 | Highest quality |
| 0001 | Lower quality | ||
| 0010 | Decreasing quality | ||
| 0100 | Decreasing quality | ||
| 1000 | Decreasing quality | ||
| 1001 | Decreasing quality | ||
| 1010 | Decreasing quality | ||
| 1100 | Lowest quality | ||
| 1101 | Quality so low that it is not useful | ||
| 1110 | L1B data faulty | ||
| 1111 | Not useful for any other reason/not processed | ||
| 6-7 | Aerosol quantity | 00 | Climatology |
| 01 | Low | ||
| 10 | Average | ||
| 11 | High | ||
| 8 | Adjacent cloud detected | 1 | Yes |
| 0 | No | ||
| 9 | Atmosphere BRDF correction performed | 1 | Yes |
| 0 | No | ||
| 10 | Mixed Clouds | 1 | Yes |
| 0 | No | ||
| 11-13 | Land/Water Flag | 000 | Shallow ocean |
| 001 | Land (Nothing else but land) | ||
| 010 | Ocean coastlines and lake shorelines | ||
| 011 | Shallow inland water | ||
| 100 | Ephemeral water | ||
| 101 | Deep inland water | ||
| 110 | Moderate or continental ocean | ||
| 111 | Deep ocean | ||
| 14 | Possible snow/ice | 1 | Yes |
| 0 | No | ||
| 15 | Possible shadow | 1 | Yes |
| 0 | No | ||
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