On clear-cut mapping with time-series of Sentinel-1 data in boreal forest

Clear-cutting is the most drastic and wide-spread change that affects the hydrological and carbon-balance properties of forested land in the Boreal forest zone1. A time-series of 36 Sentinel-1 images was used to study the potential for mapping clear-cut areas. The time series covered one and half year (2014-10-09. 2016-03-20) in a 200-km-by-200-kmstudy site in Finland. The Sentinel-1 images were acquired in Interferometric Wide-swath (IW), dual-polarized mode (VV+VH). All scenes were acquired in the same orbit configuration. Amplitude images (GRDH product) were used. The Sentinel-1 scenes were ortho-rectified with in-house software using a digital elevation model (DEM) produced by the Land Survey of Finland. The Sentinel-1 amplitude data were radiometrically corrected for topographic effects. The temporal behaviour of C-band backscatter was studied for areas representing 1) areas clear-cut during the acquisition of the Sentinel-1 time-series, 2) areas remaining forest during the acquisition of the Sentinel-1 time-series, and 3) areas that had been clear-cut before the acquisition of the Sentinel-1 time-series. The following observations were made: 1. The separation between clear-cut areas and forest was generally low; 2. Under certain acquisition conditions, clear-cut areas were well separable from forest; 3. The good scenes were acquired: 1) in winter during thick snow cover, and 2) in late summer towards the end of a warm and dry period; 4. The separation between clear-cut and forest was higher in VH polarized data than in VV-polarized data. 5. The separation between clear-cut and forest was higher in the winter/snow scenes than in the dry summer scenes.