Inclinometer measure the deformation across the borehole. This is accomplished by measuring the variation of inclination and displacement transverse to the borehole axis over time (Genske, 2006). The change in angle to one reference measurement (baseline measurement) can be converted to a distance, therefore, horizontal offsets can be measured across the landslide’s subsoil.
Piezometer measure the groundwater level. The device provides point information on the groundwater level by measuring the hydrostatic pressure head.
TDR probes (time-domain reflectometry) determine the moisture content in the subsoil along the probe. This is achieved by travel time / runtime measurement of an electrical signal. The moisture is measured automatically in fixed time intervals. Thus, enabling the selective monitoring of moisture conditions in the subsoil.
The weather station records data on the current weather at regular intervals. Accordingly, temperature, precipitation, air pressure and radiation are measured. In particular, the recording of rainfall is one of the most relevant characteristics for observations on mass movements, as it is the main trigger of landslides and mudflows in Lower Austria.
A regular field survey of points and alignment (e.g. headscarp, fissures) provides information on the nature and dynamics of slope movement (Genske, 2006). GNSS-systems offer fast and low-cost recording. Global Navigation Satellite Systems enable precise positioning on earth and with regular measurements it is possible to detect surface changes over time. GNSS is a general term for the application of existing (and future) global satellite systems for positioning (e.g. GPS, GLONASS, Galileo)
Total stations (tachymeter) are geodetic measuring instruments for precise electronic distance measurement. The travel time of an emitted light ray that is reflected at the target point is measured. If the exact geographical position of a measuring point is known, the position measurement by tachymeter is much more precise than GNSS measuring. Similar to GNSS surface changes are detectable over time given that always the same points are measured.
UAV (Unmanned Aerial Vehicle) - drone
Terrestrial Laser scanning
Laser scanning is a technique for precise distance measurements. A laser beam is emitted which scans the terrain surface with high point desity. This results in a point cloud which has the exact coordinates for each reflected point. The point cloud has such a high density that it is possible to generate very detailed and highly accurate images of the surface (so called Digital Elevation Model). The advantage of laser scanning, in contrast to the selective surface measurements as tachymetry and GNSS, is the extensive data obtained across the landslide surface while also penetration of the vegetation is possible (Höfle & Rutzinger, 2011)
Electrical resistivity tomography (ERT)
Electrical resistivity tomography is a geophysical measuring procedure. Along a transect on the soil surface electrodes are installed and energized. The electric circuit is closed by the more or less well conducting ground thereby developing a field with electric potential. As a function of the electrode assembly and soil surface topology the distribution of the specific electric resistivity can be determined. With permanent installation it is possible to deduce where and how rapid rainwater penetrates into the soil.
Wireless Sensor Network (WSN)
The wireless and thus flexible installable boxes contain an acceleration sensor. The acceleration is measured by determination of the acting inertial force. By measuring the acceleration with a very high temporal resolution changes in surface inclination can inferred. Whereby, short term changes can be promptly observed (Fernandez-Steeger et al., 2014).
- Aber, J. S., I. Marzolff, J. B. Ries & S. E. W. Aber. 2019. Small-Format Aerial Photography and UAS Imagery (Second Edition). Elsevier Academic Press
- Fernandez-Steeger, T.M. et al., 2015. Wireless Sensor Networks and Sensor Fusion for Early Warning in Engineering Geology. In G. Lollino et al., eds. Engineering Geology for Society and Territory - Volume 2. Cham: Springer International Publishing, pp. 1421–1424.
- Genske, D.D., 2006. Ingenieurgeologie: Grundlagen und Anwendung, Berlin: Springer.
- Höfle, B. & Rutzinger, M., 2011. Topographic airborne LiDAR in geomorphology: A technological perspective. Zeitschrift für Geomorphologie, Supplementary Issues, 55(2), pp.1–29.
- Jaboyedoff, M., T. Oppikofer, A. Abellán, M.-H. Derron, A. Loye, R. Metzger & A. Pedrazzini (2012) Use of LIDAR in landslide investigations: a review. Natural Hazards, 61, 5-28. 10.1007/s11069-010-9634-2
- Whiteley, J. S., J. E. Chambers, S. Uhlemann, P. B. Wilkinson & J. M. Kendall (2019) Geophysical Monitoring of Moisture-Induced Landslides: A Review. Reviews of Geophysics, 57, 106-145. 10.1029/2018rg000603