C-BAND MICROWAVE-SCATTERING FROM SMALL BALSAM FIR

An understanding of the interactions of C-band microwave energy and vegetation canopies is important in order to effectively use air- and space-borne radar sensors for monitoring ecosystems. An experiment to examine the C-band backscattering characteristics of conifer trees was conducted using a truck-mounted scatterometer. Small (1 m tall) balsam fir (Abies balsamea) were arranged at various equidistant spacings on a platform to present canopies of varying density to the radar. C-band backscattering measurements of a range of canopy densities were acquired under different polarizations and incidence angles. In addition, physical measurements of the trees were made including leaf area index, biomass, leaf and branch angle distributions, and dielectric constant. The measured backscattering coefficient from the tree canopies increased with increasing biomass, but approached a maximum at a LAI of 2.5 and fresh biomass of 3.3 kg/m2. A backscatter model was implemented using measured canopy attributes and showed close agreement with scatterometer measurements over the range of canopy densities. Model results indicated that branches were the prime scatterers of the radar while needles were found to only slightly attenuate the radar signal.