Short course in geomorphometry: Getting the most out of DEMs of Difference (co-organized)
|Convener: Tobias Heckmann | Co-Conveners: Paolo Tarolli , Wolfgang Schwanghart|
Wed, 26 Apr, 13:30–15:00
With the emergence, increasing availability, and decreasing cost of techniques to generate multitemporal high-resolution digital elevation models (LiDAR, SfM), topographic change detection has become an increasingly available tool for geomorphology. The subtraction of DEMs acquired at subsequent points in time generates a DEM of difference (DoD) representing topographic changes that can be analysed in different ways:
* Spatial patterns of negative or positive change and their magnitude can be interpreted in terms of what geomorphic process(es) caused the changes in surface elevations
* On a raster DoD, the differences on each raster cell can be readily converted to an estimate of sediment volume that has been eroded or deposited
* The cell-by-cell results can be aggregated for spatial units that are more meaningful than raster cells, e.g. landforms, hillslopes, channel reaches, (sub-)catchments etc., leading to so-called „morphological sediment budgets“
In all of these steps, the uncertainty inherent in the DEM data makes it necessary to consider how this affects what is derived from the DEM, e.g. terrain parameters, and the DoD; this can be achieved by error assessment and propagation (c.f. Lane et al., 2003; Wheaton et al., 2010).
We argue that the computation and interpretation of a DoD is only the starting point for advanced analysis. This is based on the fact that the material eroded from a cell (or any spatial unit) with negative DoD must now be somewhere downslope, and that material deposited on a cell (or spatial unit) must have been removed somewhere upslope. We will make use of these considerations for sediment budgeting on the hillslope scale.
For example, we will (i) compute sediment budgets for a sequence of hillslope segments and (ii) use flow routing algorithms to accumulate the DoD in downslope direction, leading to an estimate of sediment yield at each raster cell (c.f. Pelletier & Orem, 2014; Neugirg et al., 2016).
During the workshop, we will go through the entire work flow including
* Generation and interpretation of DoD
* DEM uncertainty assessment and propagation into (i) DEM derivates (e.g. slope), (ii) DoD, and (iii) volumetric calculations
* Advanced analysis of DoD (sediment yield, sediment budgets) and its interpretation
Basic knowledge in SAGA GIS (www.saga-gis.org), or ArcGIS (in this case we require TauDEM tools available here: http://hydrology.usu.edu/taudem/taudem5/index.html) and the availability of a laptop are an advantage but not a requirement to attend the workshop.
Attendants will receive teaching materials at the beginning of the workshop. Upon course termination attendants will be awarded with a specific certificate of attendance signed by the EGU - GM division President and by the workshop Instructors.