THE USE OF A HELICOPTER MOUNTED RANGING SCATTEROMETER FOR ESTIMATION OF EXTINCTION AND SCATTERING PROPERTIES OF FOREST CANOPIES .2. EXPERIMENTAL RESULTS FOR HIGH-DENSITY ASPEN

An analytic expression is derived that describes the backscatter power from a semi-infinite plane parallel homogeneous canopy as a function of distance from an airborne radar. This model is fitted to observed data for a high-density aspen canopy by a modification of a technique developed by A. A. Tyapkin (1960). This inversion of the model provides unbiased estimates of the canopy extinction and backscattering parameters. An active radar calibrator located underneath the canopy provides an independent method of determining the volume extinction coefficient. The results reported indicate that the coefficients change throughout the year. A comparison of these coefficients with H. J. Eom and A. K. Funk's (1984) disk model, using measured canopy properties, shows that at C-band frequency, only a part of the scattering and absorption can be attributed to the canopy leaves.