i am currently working on a project which involves the quantification of the wetness in certain areas. However it produces quite different results from what i expected. I'll describe the steps i have taken. To do so i used the ASTER global DEMv2 and clipped it to the parts to be examined. I have to clip the raster, because using the original DEM results in various errors saying "memory allocation failed". Then i calculated the slope and Catchement area via the SAGA function Catchment Area (Mass-Flux-Method, parameter: flow-spit method area cell). I also tried the Parallel and recursive method, however the results are mostly the same. Then i calculated the Topographic Wetness Index, but the results look very mixed (somewhere between a rainbow and random fuzzy bits) and values are always negative. I expected that the resulting raster should look like and display index values like the following image in the pdf PDF, page 14.
Has someone here experience with the quantification of topographic wetness in an area and could provide a tutorial how to do it right? I would appreciate using SAGA or QGIS, but i also have ArcGis 9 at Hand.
By the way: If i just use the calculate the SAGA wetness index with the clipped elevation data above, SAGA always keeps crashing (i believe because of the large no-data areas, because smaller smarts work)