I am currently trying to get in morphometry, using the SRTM 30m DEM. I was recommended to test the SAGA mudule 'Relative Heights and Slope Positions' (http://www.saga-gis.org/saga_module_doc/2.1.3/ta_morphometry_14.html) in QGIS.
It runs smoothly and I have first results, but I am a bit lost in understanding what results tell me. Does anybody of you have expert knowledge to explain what the following mean?
- Slope height (values ~0-700)
- Valley depth (values ~0-600)
- Normalized height (values ~0-1)
- Standardized height (values ~0-3000)
- Mid slope position (values ~-0,00001-1)
Input options w, t and e are also not clear to me.
If anybody of you has an idea or an idea where to find information, I would be very happy.
Best Answer
Now, the answer from the developers of the tool, who kindly allowed me to forward the answer here. I translate and do my best to reproduce what I learnt from Dr. Conrad:
The only expected input-dataset is the DEM. The tool runs an interative procedure which works with relative relief-position. The same procedure is used to calculate - the vertical distance below a terrain culmination (peak, ridge,...) - distance above the terrain minima (valley, depression,...). This is in the first step based on a drainage-oriented calculation of vertical distances ( based on Freeman, T.G.,1991: Calculating catchment area with divergent flow based on a regular grid. Computers and Geoscience, Bd. 17, 3, 413-422. [hope this is the correct publication]) and is afterwards refined iteratively to eliminate effects of watersheds.
Options W, T, E control the iterative process: 'W: The parameter weights the influence of catchment size on relative elevation (inversely proportional). T: The parameter controls the amount by which a maximum in the neighbourhood of a cell is taken over into the cell (considering the local slope between the cells). The smaller 't' and/or the smaller the slope, the more of the maximum value is taken over into the cell. This results in a greater generalization/smoothing of the result. The greater 't' and/or the higher the slope, the less is taken over into the cell and the result will show a more irregular pattern caused by small changes in elevation between the cells. E: The parameter controls the position of relative height maxima as a function of slope.'
After determination of relevant distances (below/ above), these are used to calculate standardized elevation (0= low; 1= top) and based on that we receive standardized elevation and mid slope position.
Reference: - Boehner, J. and Selige, T. (2006): Spatial prediction of soil attributes using terrain analysis and climate regionalisation. In: Boehner, J., McCloy, K.R., Strobl, J. [Ed.]: SAGA - Analysis and Modelling Applications, Goettinger Geographische Abhandlungen, Goettingen: 13-28. (find this online on the saga homepage)
To cite saga: Conrad, O., Bechtel, B., Bock, M., Dietrich, H., Fischer, E., Gerlitz, L., Wehberg, J., Wichmann, V., and Böhner, J.: System for Automated Geoscientific Analyses (SAGA) v. 2.1.4, Geosci. Model Dev., 8, 1991-2007, doi:10.5194/gmd-8-1991-2015, 2015. Available online for free http://www.geosci-model-dev.net/8/1991/2015/gmd-8-1991-2015.html