Detection of thinning cuttings using CARABAS-II VHF SAR data

Thinning cuttings constitute a considerable part of the annually harvested forest stem volume in Scandinavia. The interest to detect thinning cuttings is in the areas of global biomass monitoring in accordance with international treaties, annual local scale measurements of thinnings, forestry law enforcement, and commercial planning of the forest resource. This paper presents results from a study using the airborne CARABAS-II VHF SAR system for detection of thinning cuttings in coniferous forest stands. SAR data were acquired prior to and after thinning cuttings over 25 stands located at a test site in the southwest of Sweden. For the analysis another 24 stands were selected for reference measurements. The results from the statistical analysis show a significant difference between the reference stands and the thinning cuttings for one out of three flight paths examined. A decrease in backscatter due to thinning was found for all image pairs analyzed. Factors influencing the results such as variations in radio frequency environment, image noise variations, and removal of image artifacts have to be further investigated. Nevertheless, the proposed change detection method indicates a possibility to map thinning cuttings using CARABAS-II VHF SAR data.