Monthly Global NDVI at 5 km based on AVHRR product - 1982 to 2019

Long-term monthly NDVI calculated through daily images of AVHRR (NOAA/CDR/AVHRR/NDVI/V5), which were cloud screened and aggregated by percentile 90th on Google Earth Engine-GEE. All the images were exported from GEE to R environment where the follow procedures were executed on a pixel-basis:

1. Outlier removal based on a temporal moving window, used to identify and remove NDVI outlier values (i.e. greater or less than 1.5 standard deviation calculated on 60-months time window) 
2. Smoothing and gap filling approach implemented by the greenbrown package (TSGFssa method)

The final product is composed by 456 NDVI global images without gaps and for each month was produced an ancillary image indicating:

• Disregarded pixels: -25000 (removed) and -32000 (nodata)
• Gapfilled pixels: -20000
• Smoothed pixels: all values greater than -20000 indicate the difference between the original and smoothed AVHHR NDVI

To access and visualize the maps use: OpenLandMap.org

Publication in preparation.

All files were internally compressed using "COMPRESS=DEFLATE" creation option in GDAL.
File naming convention (veg_ndvi_avhrr_p90_5km_s0..0cm_20000101..20000131 _v1.0):

• veg = Vegetation theme
• ndvi = Normalized Difference Vegetation Index 
• avhrr = NOAA CDR AVHRR V5 product
• p90 = Percentile 90th to aggregate the daily images
• 5km = 5 km of spatial resolution
• s0..0cm = land surface as vertical reference
• 20000101..20000131 = from 2000-01-01 to 2000-01-31 (time reference)
• v1.0 = version number