Estimation of forest stem volume using ALOS PALSAR satellite images

A first evaluation of ALOS PALSAR data for forest stem volume estimation has been performed at a coniferous dominated test site in Sweden. In total, 7 Fine Beam Single polarization (FBS, look angle 34.3deg, HH-polarization) and 7 Polarimetric (PLR, look angle 21.5deg, HH-, HV-, VH-, and W- polarization) SAR images were used. In total, 56 forest stands with stem volume in the range of 45-650 m3 ha"1 (average 325 m3 ha"1) were analyzed by relating backscatter intensity to field data. The estimation accuracy of stem volume at stand level was calculated in terms of root mean square error (RMSE). For the best case investigated an RMSE of 30% was obtained using one of the FBS images acquired in the winter season. The corresponding RMSEs for the PLR images with HH-, HV-, VH-, and W-polarization were 65%, 65%, 62%, and 81%, respectively. The better results for FBS compared to PLR mode could be explained by particularly favorable weather conditions at image acquisition, or by the higher ground resolution in the FBS images, which makes small stands less sensitive to errors in geocoding.