Abstract
Abstract. With this contribution we assess the potential of unmanned aerial vehicle (UAV) based laser scanning for monitoring shallow erosion in Alpine grassland. A 3D point cloud has been acquired by unmanned aerial vehicle laser scanning (ULS) at a test site in the subalpine/alpine elevation zone of the Dolomites (South Tyrol, Italy). To assess its accuracy, this point cloud is compared with (i) differential global navigation satellite system (GNSS) reference measurements and (ii) a terrestrial laser scanning (TLS) point cloud. The ULS point cloud and an airborne laser scanning (ALS) point cloud are rasterized into digital surface models (DSMs) and, as a proof-of-concept for erosion quantification, we calculate the elevation difference between the ULS DSM from 2018 and the ALS DSM from 2010. For contiguous spatial objects of elevation change, the volumetric difference is calculated and a land cover class (bare earth, grassland, trees), derived from the ULS reflectance and RGB colour, is assigned to each change object. In this test, the accuracy and density of the ALS point cloud is mainly limiting the detection of geomorphological changes. Nevertheless, the plausibility of the results is confirmed by geomorphological interpretation and documentation in the field. A total eroded volume of 672 m3 is estimated for the test site (48 ha). Such volumetric estimates of erosion over multiple years are a key information for improving sustainable soil management. Based on this proof-of-concept and the accuracy analysis, we conclude that repeated ULS campaigns are a well-suited tool for erosion monitoring in Alpine grassland.
Highlights
Steep grassland in the montane to alpine elevation zone of the Alps is frequently affected by shallow erosion
This carrier platform is equipped with a Riegl VUX-1LR laser scanner (Riegl LMS, 2019), combined with an Applanix AP20 (Applanix, 2019) inertial measurement unit (IMU) and global navigation satellite system (GNSS) receiver as well as two calibrated oblique Sony Alpha 6000 cameras
If these points are excluded the MAE3D is reduced to 0.190 m. Excluding these four reference points, the direct georeferencing of the unmanned aerial vehicle laser scanning (ULS) point cloud is comparatively accurate in terms of horizontal alignment to the GNSS reference measurements, with a mean absolute error MAExy = 0.023 m
Summary
Steep grassland in the montane to alpine elevation zone of the Alps is frequently affected by shallow erosion. Either shallow landslides or abrasion by snow gliding processes and full-depth avalanches initially displace the vegetation, soil and unconsolidated deposits (Wiegand and Geitner, 2010). This results in patches in the grassland without a vegetation cover, where surface runoff and wind can further erode material, usually up to a few decimetres depth (Fig. 1). >30 areas per ha; Wiegand and Geitner, 2013) results in a considerable loss of soil and degradation of affected grassland (Tasser et al, 2005; Wiegand and Geitner, 2010; Alewell et al, 2015) As this reduces the capability for slope water retention, negative impacts on hydrology and hydrological hazards can arise (Wiegand and Geitner, 2013). The soil conservation protocol of the Alpine Convention, for instance, requests the monitoring and mitigation of soil erosion (CIPRA, 2005)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
