Abstract
The use of a Remotely Piloted Aircraft System (RPAS) for the characterization and monitoring of landslides has been widely improved in the last decade. In particular, the use of this system is particularly effective for the study of areas prone to geohazards. Zones affected by landslides, such as rock slides and debris flows, are often quite critical in terms of accessibility due to unstable blocs that can strongly limit the direct access to the studied area. In this paper, we present the case study of Ponte Formazza in NW Italian Alps. In June 2019, a massive and complex debris flow re-mobilized about 300,000 m3 of a rockslide deposit that occurred in 2009. In this particular environment, we tested traditional, direct and mixed photogrammetric approaches using various configurations of Ground Control Points (GCPs) of the photogrammetric block and by calculating the relative errors. The minimum configuration of GCPs was established to reduce in situ measurements without degrading the accuracy of the cartographic products. The images of three RPAS campaigns (2017, 2018 and 2019), processed with a Structure from Motion (SfM) technique, allowed us to obtain very high-resolution orthophoto and digital surface models (DSMs) before and after the 2019 event. A few GCPs, geolocated with a Global Navigation Satellite System (GNSS), improved the orthophoto and DSM quality (Root Mean Squared Error RMSE 5 cm) even in the areas far from the drone deployment. The availability of high-resolution models has been fundamental for the identification of the volume changes. Furthermore, the 3D view supported and completed the geomorphological mapping of affected areas, particularly in the areas where the field survey is dangerous. The use of ancillary meteorological data and Sentinel-2 satellite images allows for a better definition of the kinematics and the predisposal and triggering factors of the 2019 debris flow.
Highlights
In the last few years, the use of unmanned aerial vehicles (UAVs) or Remotely PilotedAircraft Systems (RPASs) in the study of natural hazards has significantly increased [1,2].The improvement of autopilot or semi-autopilot systems, high-resolution digital cameras, and Global Navigation Satellite System (GNSS) and inertial systems has allowed Remotely Piloted Aircraft System (RPAS) to increase the precision and accuracy of the data
A possible technical solution adopted for improving the quality of the GNSS position is the use of Real-Time Kinematic (RTK) receivers [3,4] onboard UAVs
We found that the direct photogrammetry solution, if not supported by precise Projection Centers Point (PCP) measurements, is less accurate than the mixed one, but the accuracies are acceptable with minimum support of only 3 ground control points (GCPs)
Summary
In the last few years, the use of unmanned aerial vehicles (UAVs) or Remotely Piloted. The improvement of autopilot or semi-autopilot systems, high-resolution digital cameras, and GNSS and inertial systems has allowed RPAS to increase the precision and accuracy of the data. Captured images are geocoded by various approaches requiring onboard and/or ground-based solutions. UAVs are usually equipped with positioning apparatuses. To improve the final positioning accuracy, ground control points (GCPs) are positioned, surveyed and used in the image post-processing. A possible technical solution adopted for improving the quality of the GNSS position is the use of Real-Time Kinematic (RTK) receivers [3,4] onboard UAVs. A possible technical solution adopted for improving the quality of the GNSS position is the use of Real-Time Kinematic (RTK) receivers [3,4] onboard UAVs
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