GIMMS AVHRR Global NDVI 1/12-degree Geographic Lat/Lon In the near future: host: http://ecocast.arc.nasa.gov/data/pub/gimms/3g/ README 2014 March 2014 ________________________________________________________________________________ 1. DESCRIPTION 2. FILE NAMING CONVENTION 3. GRID PARAMETERS 4. DATA FORMAT VI3g 5. FLAGS ________________________________________________________________________________ 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=0.833 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) END