I'm trying to generate rasters whose values summarize the mean value of a given parameter (slope, curvature, etc.) of the upslope terrain. I feel like this should be doable using only a flow direction raster and a raster of the parameter of interest, but I don't really know where to begin. I've seen this instruction http://forums.esri.com/Thread.asp?c=93&f=995&t=303114, but I can't seem to figure out a way to interpret it that produces a result that makes any sense. I'm familiar with ArcMAP, QGIS, SAGA, and a bit of GDAL and GRASS, so I'll gladly accept instructions for any of these platforms.
Thanks for the reply. I actually figured it out yesterday and hadn't had a chance to mark this as "solved." I had been interpreting the advice on the ESRI forums as the following steps:
- Create a slope raster, then run the flow accumulation tool on it.
- Create a raster with a constant value, then run the flow accumulation tool on it.
- Divide result from step 1 by result from step 2.
This didn't make very much sense to me, but I tried out a couple variations anyway, with interesting but nonsensical results. Eventually, I realized that what I was supposed to be doing was running flow accumulation weighted by the slope values (sum of slope uphill from a cell), then dividing this by the unweighted accumulation (total area uphill from the same cell). So, even though I initially misinterpreted this advice, it did get me looking in the right direction.