Mapping of wind-thrown forests using CARABAS-II VHF SAR image data

Heavy storms are causing severe damage worldwide to forested land every year. The devastating storms that struck central Europe in late 1999 destroyed the equivalent of several years of normal forest harvesting, amounting to very large economical sums. Therefore, rapid mapping of damaged areas is of major importance for assessment of short-term actions as well as for long-term reforestation purposes. In this paper, the use of airborne CARABAS-II VHF (20-90 MHz) SAR imagery for high spatial resolution mapping of wind-thrown forests has been investigated and evaluated. The investigation was performed at a test site located in southern Sweden, dominated by Norway spruce forests. A regression model predicting forest stem volume from radar backscattering amplitude was used to retrieve stem volume for storm-damaged areas. Finally, the predicted volumes were compared with subjectively inventoried stem volumes. Unexpectedly, the results indicate that the backscattering amplitude is considerably higher for wind-thrown forests in comparison with backscattering from unaffected forests. Nevertheless, this finding implies that VHF SAR imagery has potential for mapping wind-thrown forests, preferably using change detection techniques of images acquired prior to and after storm-fellings