Who I am
I am a diploma student at the department of Physical Geography, Trier University (Germany). I work in the field of experimental rill erosion research. My main activity and diploma thesis focuses on terrestrial close-range-photogrammetry.
The awarded poster presents terrestrial photography as a method to identify sediment sources in eroding rills as an extension of the existing in-field rill experiments.
Soil Erosion caused by water is, beneath human activity, one of the main causes for global soil loss. Especially water that is moving in rills seems to have a large fraction in the overall amount of lost soil. In order to assess this amount of eroded material, we set up a rill experiment, which is in use for about eight years now. Many parameters like shear strength, inclination, flow velocity were gathered before and during the rill experiment, but the exact places of the sediment sources were still unknown. Therefore a device (GNAG = Geländenahabtastgerät = short range surface sensoring device) was to be conceptualized that would enable us to identify these sources using terrestrial close-range-photogrammetry.
As we could not find any literature concerning rill erosion and photogrammetry in close connection, we had to adapt the means of aerial photogrammetry to our ‘flight altitude’ of around one meter above ground. Several cameras and mountings were used and different software environments were tested.
Method and its Evolution
At an elementary stage, we decided that the simultaneous employment of two identical inexpensive cameras (‘stereo pictures’) would be more sensible than the repeated installation of one (expensive) digital single lens reflex (DSLR) camera. Despite that, we decided to take pictures with both camera systems in the first experiments for comparison purposes.
In the end we found out that a push-rod mounting with a balljoint mounted on top of a tripod would be an affordable equipment. The balljoint is necessary to compensate the influences of the topography (inclination).
The software to be applied has to be highly adjustable, affordable and, in contrast to e.g. Leica photogrammetry suite, it has to be able to work without ground control points. Therefore, we decided to use an open-source product, VisualSFM, which contains the structure-from-motion-technology. This software is able to create a 3-D-point cloud out of the glut of images, which finally can be transformed into three-dimensional solids. With the help of the two solids that belong to each rill experiment (before experiment/after experiment), we are enabled to (a) estimate the differences in volume and (b) identify places were soil is detached and accumulated.
In February/March 2013, several hundred pictures of three rills in Navarra/Spain were taken, afterwards 3-D-point clouds and resulting models have been computated. Our experience shows that rills having a length of about 20m are hard to computate because of the vast reconstruction time required. It also showed us that the use of a single DSLR is only reasonable in addition to the ‘stereo pictures’ made by the GNAG.
We will double the number of mounted cameras to systematically increase the number of camera positions. This will enable us to get the minimum overall number of indispensable images and simultaneously increase the quality of point clouds and resulting solids by ensuring a constant overlap between the picture sets.
Wirtz, S.; Iserloh, T.; Rock, G.; Hansen, R.; Marzen, M.; Seeger, M.; Betz, S.; Remke, A.; Wengel, R.; Butzen, V.; Ries, J.B. (2012): Soil Erosion on Abandoned Land in Andalusia: A Comparison of Interrill- and Rill Erosion Rates. ISRN Soil Science, Volume 2012, Article ID 730870, 16p.
Wirtz, S.; Seeger, M.; Remke, A.; Wengel, R.; Wagner J.F.; Ries, J.B. (2013): Do deterministic sediment detachment and transport equations adequately represent the process-interactions in eroding rills? An experimental field study. Catena 101, 61-78.
Johannes B. „Chef du tout“ Ries:
Prof. Dr. Johannes B. Ries is the driving force behind the whole erosion research programme at Trier University. His dedication convinces us to carry on experimental work even under sickening weather conditions.
Dr. Manuel „Troubleshooter“ Seeger:
No problem in the study area is big enough, not to be solved by Manuel within the shortest span of time. He is the person, who is constantly watching that all the different experiments are carried out in a way that ensures the possibility of connecting the results.
Dr. Stefan „The Rill“ Wirtz:
Stefan is inventor and permanent improver of the in-field rill-experiment. His “scary” kind of leadership encourages us to do an accurate job and he therefore usually delivers highly satisfactory results.
Olli “The Nerd” Gronz:
Olli is the man who is responsible for all endless tasks concerning computer and software. Without his skills, the structure-from-motion-project would have suffered from much more delay. He won’t ever be found out in the field because of his aversion of dust and dirt.
Kerstin “Sponge” Becker:
Faster than Google, Kerstin instantly knows where to find all kinds of files, things and instruments. For approximately half a year, she is all smiles and graces and therefore now an indispensable member of our little rill-erosion-research group.
- E-mail: firstname.lastname@example.org
- Dpt. of Physical Geography, FB VI — Geography/Geosciences, Trier University, Campus II, Behringstr., D-54286 Trier, Germany