Relative Greenness (RG) ranges from 0-100% and indicates how green each 500-m square pixel of land is in relation to a 10-year historical (2003-2012) database of greenness values for that particular pixel. An RG value of 100% signifies that this is the highest greenness level ever reached during the multi-year period, while an RG value of 0% indicates that this is the lowest greenness level reached over that same period. RG is calculated daily from the past 7 days of MODIS satellite imagery using NDVI (Normalized Difference Vegetation Index). The calculation also involves a smoothing routine to filter out unrealistic daily rises and drops in greenness. If a given pixel is cloudy during the entire weekly period, the RG value used is taken from the last available valid value for that pixel. RG is a very important variable in the fire danger model used in OK-FIRE. It is used to model live fuel moisture (herbaceous and woody) and to apportion the fuel load distribution between 1-hour dead fuels and live herbaceous and live deciduous woody fuels.
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