Environmental change detection in prairie landscapes with simulated Radarsat 2 imagery

摘要

For the past decade, we have been using Landsat TM imagery to monitor changes in the area and distribution of ecosystems in a relatively undisturbed natural region in southwestern Manitoba, Canada. The 40,000 hectares of Canadian Forces Base Shilo are protected from urbanisation, commercialisation and agriculture, and are disturbed only by modest and controlled amounts of military training. A significant problem with the use of TM imagery for this study is that some of the more sensitive indicators of environmental change, such as the infestation of disturbed grassland by leafy spurge, are very difficult to identify and delineate in the visible and near-IR bands. A fully polarized SAR that is sensitive to vegetation morphology may not have the same difficulty. C band radars, such as that being constructed for Radarsat 2, are known to have difficulty differentiating vegetation types in regions of dense foliage, but, in a prairie ecosystem such as the one under study here, even the densest foliage should be sparse enough to yield a unique polarisation signature. In order to test this hypothesis we have simulated Radarsat 2 HH, HV and VV images, using several TM images of the area, polarisation ratios extracted from the literature for vegetation types similar to those found in the area, and a Radarsat 1 HH image of the area collected almost simultaneously with one of the TM images. Comparison of synthesized imagery from different years shows sufficient differences to imply that Radarsat 2 imagery will likely be a useful tool for continuing our prairie ecosystem monitoring and assessment.