January 22, 2017       

Predictive Services - Fuels / Fire Danger - Greenness Defined

Satellite-derived vegetation index maps of the contiguous United States have been available since 1989. The basic data source for these maps is the Advanced Very High Resolution Radiometer (AVHRR), which is an instrument on board the National Oceanic and Atmospheric Administration's (NOAA) polar orbiting weather satellites. The U.S. Geological Survey (USGS), Earth Resources Observation Systems (EROS) Data Center (EDC), in South Dakota, retrieves satellite data daily, processes it, and produces normalized difference vegetation Index (NDVI) maps that reflect the quantity of actively photosynthesizing biomass on the landscape. Cloud-free observations of the land surface are necessary for monitoring vegetation. Therefore the USGS composites the AVHRR data collected over the period of a week to produce a nearly cloud-free data set. The spatial resolution of the AVHRR is 1.1 km when the satellite is directly overhead. Thus, a square, 1.1 km on a side, is the ground area represented by each picture element, or pixel. During the course of the week the highest NDVI value for each pixel is retained for inclusion in the weekly data set. The data set is made available by the EROS Data Center for use by fire managers. The Fire behavior Research Work Unit at the Intermountain Fire Sciences Laboratory in Missoula, Montana, has developed some software to "calculate" the four weekly maps that appear on this page. They are described below.

This map indicates current vegetation greenness compared to an historically observed NDVI range. Any pixel appears fully green when the NDVI for that pixel reaches it maximum historical value, and fully cured when its NDVI value reaches its historical minimum. Values range from 0 to 100; 0 when the vegetation has reached its lowest historical value, and 100 when it reaches its highest value.

This map portrays current NDVI values for each pixel compared to a very green reference such as an alfalfa field. Dry areas typically will have low visual greenness values because their NDVI values are usually low, and lush areas typically have high visual greenness values because their NDVI is generally high. Visual greenness values range from 0 to 100.

This map provides calculated values for live shrub moisture for each pixel (1.1 square kilometer) on the map. An algorithm is used to estimate the live shrub fuel moisture for each pixel, based on the relative greenness value that has been calculated for that pixel, and on the historical maximum and minimum NDVI values for that pixel. Several assumptions have been made in order to produce the map. It is assumed that maximum live shrub moisture ranges from 100 to 250 percent, and that minimum live shrub moisture range from 50 to 90 percent. Minimum live shrub moisture of less than 50 percent have been measured in Arizona, but are uncommon.

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    FBK RAWS station, air temperature: -25F
Reading taken at: 2017-01-22 14:00

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Reading taken at: 2017-01-22 14:00
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