Cucchiaro S., Cavalli M., Vericat D., Crema S., Marchi L., Cazorzi F., 2017, From SfM photogrammetry to DoDs_ a methodological workflow to monitor topographic changes in a debris-flow catchment, 12 Convegno GIT - Geology and Information Technology, Gavorrano (GR), 12-14/06/2017,
URL: http://www.cnr.it/prodotto/i/373402

Debris-flow catchments are characterised by remarkable geomorphic changes that can occur with high frequency. Accordingly, monitoring topographic changes induced by these processes requires high-resolution surveys acquired with high frequency. Recent photogrammetric techniques, such as Structure from Motion (SfM) and Multi-View Stereo (MVS), represent a low-cost opportunity for acquiring multi-temporal high-resolution topography. However, these techniques need important steps of data processing and uncertainty analysis to identify and filter erroneous or unwanted data, that may have a significant effect on the estimates of topographic changes. Within this context, in this paper we present a methodological and standardized workflow for_ i) data-acquisition and post-processing to obtain usable and accurate Digital Terrain Models (DTMs) and ii) error analysis to assess uncertainty in the study of topographic changes through DEM-differencing analysis (DEMs of Difference or DoD). This workflow is based in the application of SfM and MVS techniques and was developed and tested in a small area of the Moscardo catchment (eastern Italian Alps). Multi-temporal SfM-MVS photogrammetry based on images taken from the ground and by means of UAV were carried out before and after three debris-flows occurred between June and July 2016. The developed workflow involves the following steps_ (a) point cloud generation through the application of SfM-MVS; (b) analysis of the precision and accuracy of the Ground Control Points (GCPs) and the resultant point clouds by means of Check Points (CPs); (c) data filtering, cleaning and decimation through geostatistical tools; (d) evaluation of the need to carry out the alignment of multi-temporal point clouds; (e) DTMs generation; (f) assessment of a minimum Level of Detection (minLoD) based on data precision; (g) DoDs preparation and thresholding based on the minLoD; (h) assessment of topographic changes.

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