Dating and relating kim sarrasin
Following the top-down approach requires that spatial objects in the images be identified starting at the coarser level, and gradually to finer levels, according to the size of the objects of interest : wetlands, water bodies, mineral surfaces, forest, etc.Generally 3 segmentation levels are required: The coarse levels allow toidentify large spatial ensembles.Satellite image types used for CWI are RADARSAT-1 and Landsat-ETM.The Landsat-ETM images are acquired, when possible, in summer at a time when vegetation exhibit high level of activity and Radarsat images must be acquired during spring flood or during a period of high water in fall.This level also allows to identify medium size wetlands.Lastly, the fine level is the refinement of the medium level, composed exclusively of « Potential Wetlands - Medium » class.The method was tested on 5 study sites : Radisson, lac Saint-Pierre, lac Saint-François (Appalachian), Grande-Plée-Bleue and Isle Verte.
The medium level is the refinement of the coarse level, primarily on « Potential Wetlands » class.
The multi-level segmentation allows wetland identification at levels that best fit variable wetland sizes.
The 5 wetland classes at a regional scale are well suited to thematic mapping using satellite remote sensing. northern Great Plains since 1996, an increase (460 %, 1,048 birds; 67.7 % increase since 1991) was detected on the Missouri River.
The smallest wetlands are identified at this level, but always keeping in mind the spatial objects must be larger than 1 ha to be compatible with the CWI minimum mapping unit.
Hierarchical classification optimizes wetland identification and reduces multi-class confusion.