ESTIMATION OF FOREST BIOPHYSICAL CHARACTERISTICS IN NORTHERN MICHIGANWITH SIR-C X-SAR/

A three-step process is presented for estimation of forest biophysical properties from orbital polarimetric SAR data, Simple direct retrieva l of total aboveground biomass is shown to be ill-posed unless the eff ects of forest structure are explicitly taken into account, The proces s first involves classification by 1) using SAR data to classify terra in on the basis of structural categories or 2) a priori classification of vegetation type on some other basis, Next, polarimetric SAR data a t L- and C-bands are used to estimate basal area, height and dry crown biomass for forested areas. The estimation algorithms are empirically determined and are specific to each structural class, The last step u ses a simple biophysical model to combine the estimates of basal area and height with ancillary information on trunk taper factor and wood d ensity to estimate trunk biomass, Total biomass is estimated as the su m of crown and trunk biomass. The methodology is tested using SIR-C da ta obtained from the Race Supersite in Northern Michigan on Apr, 15, 1 994, This site is located at the ecotone between the boreal forest and northern temperate forests, and includes forest communities common to both. The results show that for the forest communities examined, biop hysical attributes can be estimated with relatively small rms errors: 1) height (0-23 m) with rms error of 2.4 m, 2) basal area (0-72 m(2)/h a) with rms error of 3.5 m(2)/ha, 3) dry trunk biomass (0-19 kg/m(2)) with rms error of 1.1 kg/m(2), 4) dry crown biomass (0-6 kg/m(2)) with rms error of 0.5 kg/m(2), and 5) total aboveground biomass (0-25 kg/m (2)) with rms error of 1.4 kg/m(2), The addition of X-SAR data to SIR- C was found to yield substantial further improvement in estimates of c rown biomass in particular, However, due to a small sample size result ing from antenna misalignment between SIR-C and X-SAR, the statistical significance of this improvement cannot be reliably established until further data are analyzed, Finally, the results reported herein are f or a small subset of the data acquired by SIR-C/X-SAR, Future efforts will examine the role of incidence angle and environmental conditions on the retrieval process.