Earth flows are complex gravitational events characterised by a heterogeneous displacement pattern in terms of scale, style, and orientation. As a result, their monitoring, for both knowledge and emergency purposes, represents a relevant challenge in the field of engineering geology. This paper aims to assess the capabilities, peculiarities, and limitations of different remote sensing monitoring techniques through their application to the Pietrafitta earth flow (Southern Italy). The research compared and combined data collected during the main landslide reactivations by different ground-based remote sensors such as Robotic Total Station (R-TS), Terrestrial Synthetic Aperture Radar Interferometry (T-InSAR), and Terrestrial Laser Scanner (TLS), with data being derived by satellite-based Digital Image Correlation (DIC) analysis. The comparison between R-TS and T-InSAR measurements showed that, despite their different spatial and temporal resolutions, the observed deformation trends remain approximately coherent. On the other hand, DIC analysis was able to detect a kinematic process, such as the expansion of the landslide channel, which was not detected by the other techniques used. The results suggest that, when faced with complex events, the use of a single monitoring technique may not be enough to fully observe and understand the processes taking place. Therefore, the limitations of each different technique alone can be solved by a multi-sensor monitoring approach.

The monitoring of slopes’ dynamics is essential to ensure the safety of infrastructures exposed to landslide risk and to develop mitigation strategies. However, it is not always possible to perform proper and slope-distributed monitoring due to the high cost of professional instruments. In this context, we developed a low-cost Arduino©-based wire extensometer for landslide monitoring. This instrument is capable of measuring the bi-directional distance between two fixed points, which is useful in landslide areas to observe linear displacements over time. Traditional wire extensometers are equipped with potentiometers, which allow measuring only finite displacements. Instead, our low-cost extensometer exploits a capacitive rotary encoder, which is able to measure infinite displacements. In addition, the new instrument can measure both wire lengthening and shortening, thanks to a spring-loaded winding system. Furthermore, the instrument’s settings can be modified to reach a millimetric resolution. The device - developed on an Internet of Things (IoT) project - is equipped with an online data transmission system and with a data-log system for local data storage. Laboratory and field tests were carried out with the aim of evaluating the instrument’s accuracy and reliability. Preliminary results demonstrate the great potential of this low-cost sensor for displacement measuring in the field of landslide monitoring.

Earth flows are complex geological processes that, when interacting with linear infrastructures, have the potential to cause significant damage. Consequently, conducting comprehensive investigations and continuous monitoring are becoming paramount in designing effective mitigation measures and ensuring sustainable risk management practices. The use of digital image correlation (DIC) algorithms for the displacement monitoring of earth flows is a relatively new and growing field with a limited number of dedicated works in the literature. Within this framework, the present paper contributes by evaluating DIC techniques at several earth flow sites. These assessments were founded upon data obtained from both low-cost and multi-platform sensors, used to assess the displacement field, pinpointing the most active sectors, and gauging their rates of movement during different kinematic phases. In this regard, the highest localized movement velocities reached in the Pietrafitta (0.01 m/day) and Grillo (0.63 m/day) earth flows experience different ongoing kinematic processes. The versatility of these techniques is notable, manifesting in the ease of installation, cost-effectiveness, and adaptability to various platforms. The proven reliability in terms of maximum accuracy (1 pixel) and sensitivity (0.05 m) lays the foundation for the extensive use of the presented techniques. The amalgamation of these attributes positions DIC techniques as competitive, adaptable, and readily deployable tools in earth flow studies.