Mapping fire scars using Radarsat-2 polarimetric SAR data

Climate change is increasing the frequency and size of wildfire events in Canada's forests. The size, distribution, and remoteness of boreal forest fire events make them a challenge to accurately monitor. Radarsat-2 is all-weather radar technology and offers high spatial resolution, cross polarization, polarimetric capabilities, and a wide swath width. In this paper, Radarsat-2 fine quad-pol data were analyzed utilizing the polarimetric phase information to map historical fire scars over two main study sites. The study demonstrated that historical fire scars, less than 10 years old and without strong topographic variation, had distinct polarimetric signatures with relatively higher quad-pol probabilities, leading to detection with low false alarm rates. By combining polarimetric decomposition and new classification approaches, fire scars were extracted; the resulting burned areas matched the true burned areas according to GIS polygons from the provincial forest fire database. Our new K-Nearest Neighbors Graph Clustering classifier, unlike the classical Wishart scheme, does not depend on backscatter intensity; it relies more on polarization information, and is more tolerant of topographic variations. These new approaches have revealed an exciting new application, mapping historical fire scars with polarimetric radar.