General Data Description And Access

GIMMS AVHRR Global NDVI 1/12-degree Geographic Lat/Lon In the near future.

The AVHRR NDVI3g data may be downloaded directly here:

http://ecocast.arc.nasa.gov/data/pub/gimms/3g/

The data set is also available to all NEX users in the datapool located here:

/nex/datapool/gimms/3g/

The data can also be accessed on amazon's S3, s3://nasanex/AVHRR/GIMMS/


README 2014 March 2014
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1. DESCRIPTION
2. FILE NAMING CONVENTION
3. GRID PARAMETERS
4. DATA FORMAT VI3g 
5. FLAGS
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1. DESCRIPTION

This dataset is an inverse cartographic transformation and mosaicing of the 
    GIMMS AVHRR 8-km Albers Conical Equal Area continentals AF, AZ, EA, NA, and
    SA to a global 1/12-degree Lat/Lon grid.

Continent demarcation and pixel selection is predetermined with an ancillary
    NDVI-3G based land-water mask.

2. FILE NAMING CONVENTION

geo[year][month][period].n[sat][-[VI][version]g

where 
          year     2-int   2 digit year
          month    3-char  abbr. lower case month name
          period   3-char  alphanum period: bimonthly 15[ab]
          sat      2-int   satellite number
          version  n-int   version number (3)

For example,

geo09jan15a.n17-VI3g

3. GRID PARAMETERS

grid-name: Geographic Lat/Lon
    pixel-size: 1/12=0.0833 degrees

size-x: 4320
    size-y: 2160

upper-left-lat: 90.0-1/24
    upper-left-lon: -180.0+1/24
    lower-right-lat: -90.0+1/24
    lower-right-lon: 180.0-1/24

*coordinates located UL corner of pixel

4. DATA FORMAT - VI3g

datatype: 16-bit signed integer
    byte-order: big endian

scale-factor: 10000
    min-valid: -10000
    max-valid: 10000
    mask-water: -10000
    mask-nodata: -5000

*values include embedded flags (see full NDVI-3G documentation - in preparation)

5. FLAG VALUES
    Each NDVI data set (ndvi3g) is an INT16 file saved with ieee-big_endian
    it ranges from -10000->(10000->10004)
    with the flagW file added to the ndvi values as follows:
    ndvi3g = round(ndvi*10000) + flagW - 1;
    flagW ranges from 1->7
    to retrieve the original ndvi  and flagW values
    flagW = ndvi3g-floor(ndvi3g/10)*10 + 1;
    ndvi = floor(ndvi3g/10)/1000
    The meaning of the FLAG:
    FLAG = 7 (missing data)
    FLAG = 6 (NDVI retrieved from average seasonal profile, possibly snow)
    FLAG = 5 (NDVI retrieved from average seasonal profile)
    FLAG = 4 (NDVI retrieved from spline interpolation, possibly snow)
    FLAG = 3 (NDVI retrieved from spline interpolation)
    FLAG = 2 (Good value)
    FLAG = 1 (Good value)
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