Detection of old scattered windthrow using low cost resources. The case of Storm Xynthia in the Vosges Mountains, 28 February 2010

Unlike the contiguous windthrows, the scattered windthrows occurring as a result of wind gusts of lower speed (100-140 km/h) than in the first case (>140 km/h) are much more difficult to detect due to their much smaller areas and due to their very large number (several hundred in the wooded Vosges Mountains). The objective of this research is to present a rapid procedure for the detection of the scattered windthrows based on low cost, Landsat type images, knowing that certain sensors cannot be accessed without significant investments. Our application is based on the study of effects caused by the Storm Xynthia in the Vosges Mountains in the North-East of France, on 28 February 2010. Thus, based on two sets of Landsat satellite images, we used the dark object approach and the Disturbance Index, as well as the image classification before and after the storm, resulting in a map of changes. Following the detection process, 257 scattered polygons were detected, totalling 229 ha. For validation purposes, high-resolution images and orthophotoplans taken before and after storm were used. The error matrix was calculated, achieving an overall accuracy of 86%, which confirmed the quality of our analysis and supported this procedure for detecting scattered windthrow based on low cost resources.