Figure 4 - uploaded by Wenzhu Hou
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Slope angle map of the study area and its adjacent area and overlaid with an ortho-rectified 1963 aerial photo
Source publication
Establishing landslide models plays a critical role in Natural Terrain Hazard Studies (NTHS). Conventional approaches adopted by NTHS practitioners may be subject to temporal and spatial limitations. In particular, landslide volume estimations are prone to inaccuracies using conventional approaches including direct, field-based measurements due to...
Contexts in source publication
Context 1
... establish a digital 3D ground model; (2) investigate topographic, hydrological and geomorphological features; and, (3) assist in determining geomorphological units by automated landform classification as part of the development of a geomorphological model for the study area. According to the slope angle map derived from the DEM (Figure 4), the study area is characterised by three sub-horizontal bands of steeply (i.e. >45°) slopes at 350 mPD to 360 mPD (Upper band), 330 mPD to 340 mPD (middle band) and 300 mPD to 310 mPD (lower band). ...
Context 2
... stream network was generated from the DEM-based hydrological modeling (using various ArcGIS tools, e.g. flow direction, flow accumulation, stream order etc.) and is shown in Figures 4 and 5. The main streamcourse at the study site had flowing water during the entire observation period of May to December 2020 although water levels were observed to be minimal in May (i.e. at the start of the 'wet' season) and in December (i.e. within the 'dry' season). ...
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Citations
... First, the unavailability of instant measurement after the landslide, given the time required to gain a safe field access to the scar, slows down the response in risk mitigation. Second, the conventional assumption of ellipsoidal landslide geometry may not fit the actual natural terrain landslides in Hong Kong (Hou et al., 2021). ...
... Second, to achieve a more accurate source volume estimation, filtering the vegetation signals from the landslide scars is another optional procedure; the detailed steps can be referenced in Hou et al. (2021). ...
... The consistent records from the traditional field-based measurements in GEO Report No. 233 have validated the feasibility of this remote sensing approach. On the other hand, by applying the same digital method of using a UAV-based SfM photogrammetry to construct a landslide 3D model, the acceptable range of result variations between this study and Hou et al. (2021) has proven the consistency of this methodology. Therefore, not only has this adventurous digital approach demonstrated its practicability, but also it reveals a trend of shifting from rasters towards point clouds, more dependence in the future on processing voxels directly instead of pixels. ...
In adapting to rapid urban development and changing climate, the geotechnical industry is
shifting towards harnessing digital technologies in Natural Terrain Hazard Study (NTHS) for landslide investigation. In this paper, we adopted a new digital method using multi-temporal point cloud models and digital elevation models derived from various available resources for the assessment of landslide source volume and dimensions. These resources include (1) historical aerial photographs from territory-wide aerial photographic survey carried out by the Lands Department, (2) project-specific UAV photographic and video surveys, and (3) the territory-wide airborne LiDAR surveys data. Two case studies from the Fei Ngo Shan area, Hong Kong, were carried out. Case 1 involves two recent landslides that occurred in 2005, and Case 2 involves a cluster of eight recent landslides that occurred in 2020. All these ten landslides were carefully investigated using conventional methods (e.g., field measurement or API) by GEO and GeoRisk Solutions, respectively. These investigation results were taken as legacy records for a comparison
with the results derived from our adopted digital method. The comparison shows that the
landslide source volume derived from the digital method is similar to the legacy record. This paper assessed the feasibility and accuracies of aligning and comparing digital models derived from multi-sources for landslide studies.
