RADAR-DERIVED STANDWISE FOREST INVENTORY

The application of remote sensing methods in the estimation of forest stand characteristics, especially biomass and stem volume, has been in tensively investigated during the last few years. The new methods, how ever, have not been accurate enough for operational standwise inventor y with a required accuracy typically of 15% for main stand characteris tics (stem volume, basal area, and mean height). The present work demo nstrates the feasibility of a nonimaging helicopter-borne ranging scat terometer for standwise forest inventory. The radar-derived stand prof iles were compared with the standwise field inventory data by applying multivariate data analysis methods. The 1300 ha Teijo test site, loca ting 130 km west of Helsinki, was divided into 18 parallel radar fligh t lines with a 150 m spacing. A total of 28 radar variables, including profile information and ground and crown backscatter contributions at 5.4 and 9.8 GHz (polarizations VV, HV, and HH), were used in regressi on model development. The capability of a ranging radar to classify de velopment class, land use class, bog type and fertility (site) class w as demonstrated for the first time. The accuracy of the radar derived estimates for mean height was 1.6 m (13%) meeting the requirement of o perational use. The obtained stem volume accuracy of 31 m(3)/ha (26%) was slightly better than has been obtained by aerial photographs. The accuracy of stem volume estimation could be easily improved by decreas ing the space between flight lines. However, this leads to considerabl e increase in flight costs, and, therefore, a scanning ranging radar c apable of producing three-dimensional (3-D) images of forests would be a better alternative.