As fuels dry seasonally, the amount of energy required to burn off the water decreases and fire hazard increases. A pixel is typically comprised of several materials within the field of view. Spectral Mixture Analysis decomposes this mixed spectrum into several pure spectra, called endmembers, weighted by the proportion of the endmember within the field of view. The Green vegetation fraction provides an areal estimate of green leaf cover and the NPV fraction provides an estimate of the dead fraction. Seasonal changes in water vapor respond to specific humidity.
Liquid water is a measure of water present in canopies.
The total canopy moisture provides an estimate of the amount of water a fire would need to evaporate to spread. Radar backscatter responds to the size of elements within a canopy and their moisture content. Long wavelength radar, such as L and P band, respond primarily to woody components. As canopies age and accumulate woody biomass, radar backscatter increases. Above a threshold of biomass, backscatter saturates.