Sensitivity of ERS-1 and JERS-1 radar data to biomass and stand structure in Alaskan boreal forest

Thirty-two boreal forest sites were identified and sampled in the central region of Alaska to evaluate the sensitivity of the C-band ERS-1 and the L-band JERS-1 radar platforms to site biophysical properties. A growing body of research has shown a significant radar backscatter response to biomass in a variety of forest systems. Alaskan boreal forests may be well suited to radar remote sensing. The sites selected represent black spruce (Picea mariana) and white spruce (Picea glauca) stands in a post-fire chronosequence. Black spruce biomass ranged from less than 1 kg/m2 to 5.6 kg/m2 and white spruce from 8.8 to 21.5 kg/m2. Results indicate both ERS-1 and JERS-1 backscatter is responsive to biomass, density, and height, though other factors, principally surface moisture conditions, are often a stronger influence. Sensitivity to forest biomass and structure appears greatest when surface moisture conditions are minimized as a factor. Biomass correlations with the radar backscatter were strongest in the late winter imagery when all sites had a snow cover, and late summer when the surface is most dry. ERS-1 data may be more sensitive to surface moisture conditions than the JERS-1 data due to the shorter wavelength of the C-band sensor, though this is inconclusive because of limited JERS-1 L-band data for comparison. Also, though the ERS-1 platform has proved to provide a very stable signal, results must be interpreted with caution as the dynamic range for our study sites is often less than 4 dB, and the uncertainty of the backscatter estimate is ±1.5 dB.