Improving GNSS Landslide Monitoring with the Use of Low-Cost MEMS Accelerometers

Observation and monitoring of landslides and infrastructure is a very important basis for land planning, human activities, and safety. Geomatic techniques for deformation monitoring have usually involved GNSS and total station measurements or, more generally, expensive geodetic instruments, but other techniques, such as SAR (Synthetic Aperture Radar), can be efficiently applied. Using low-cost sensors could be an interesting alternative solution if the accuracy requirements can be satisfied. This paper shows the results obtained for tilt measurements using MEMS accelerometers, which were combined with mass-market GNSS sensors for monitoring five sites located on landslides. The use of a MEMS-like inclinometer requires an important calibration process to remove bias and improve the solution’s accuracy. In this paper, we explain the MEMS calibration procedure employed, with a simple and cheap solution. The results indicate that with a simple calibration, it is possible to improve measurement accuracy by one order of magnitude, reaching an angular accuracy of a few hundredths of a degree, verified by an independent technique

Il monitoraggio dei movimenti e delle deformazioni con tecniche geomatiche di basso costo

L’osservazione dell’evoluzione di fenomeni di dissesto ha una importanza strategica sul nostro territorio. Un importante precursore di fenomeni franosi è il movimento o la deformazione degli stessi: tali parametri possono essere osservati con tecniche geomatiche. Le misure topografiche o GNSS con ricevitori geodetici (multi-frequenza e multi-costellazione) sono ormai ben consolidate nel trattamento e nella precisione. La realizzazione di sistemi basati su questi sensori non è tuttavia a basso costo, specie se consideriamo tecniche GNSS applicate su molti punti di controllo per una descrizione dettagliata del fenomeno, o installazioni soggette a pericoli oggettivi e dunque da considerarsi praticamente “a perdere”. Ricevitori GNSS singola frequenza sono oggi reperibili a costi minori di cento euro e possono, sotto opportune ipotesi e ingegnerizzazioni, costituire alternative ai ricevitori geodetici. Nell’ambito di un progetto di ricerca finanziato da CSI Piemonte per lo studio di tecnologie di monitoraggio a basso costo, sono stati sviluppati sistemi di acquisizione, trasmissione ed elaborazione dati basati su sensori GNSS singola frequenza di minuscole dimensioni. Il sistema costituisce una sorta di piccola stazione permanente GNSS, integrata con accelerometri per la stima di inclinazione e vibrazioni e con sensori meteorologici. È corredata di micro PC con processore ARM e interfacce di comunicazione wireless a lungo raggio per la trasmissione in tempo reale delle misure. Il sistema risulta caratterizzato da consumi elettrici molto contenuti ed è di rapida installazione in siti anche complessi dal punto di vista dell’accesso, dell’alimentazione e comunicazione. Vengono esposti nella nota i risultati delle prove di accuratezza dei sensori GNSS eseguite in laboratorio, le procedure di calibrazione dei sensori e la loro ingegnerizzazione, oltre ai primi risultati sulle installazioni situate nel nord del Piemonte su alcune zone di dissesto

Improving GNSS Landslide Monitoring with the Use of Low-Cost MEMS Accelerometers

Observation and monitoring of landslides and infrastructure is a very important basis for land planning, human activities, and safety. Geomatic techniques for deformation monitoring have usually involved GNSS and total station measurements or, more generally, expensive geodetic instruments, but other techniques, such as SAR (Synthetic Aperture Radar), can be efficiently applied. Using low-cost sensors could be an interesting alternative solution if the accuracy requirements can be satisfied. This paper shows the results obtained for tilt measurements using MEMS accelerometers, which were combined with mass-market GNSS sensors for monitoring five sites located on landslides. The use of a MEMS-like inclinometer requires an important calibration process to remove bias and improve the solution’s accuracy. In this paper, we explain the MEMS calibration procedure employed, with a simple and cheap solution. The results indicate that with a simple calibration, it is possible to improve measurement accuracy by one order of magnitude, reaching an angular accuracy of a few hundredths of a degree, verified by an independent technique

Debris Flow and Rockslide Analysis with Advanced Photogrammetry Techniques Based on High-Resolution RPAS Data. Ponte Formazza Case Study (NW Alps)

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

High accuracy gravitational red-shift evaluation at INRIM

The gravitational redshift is presently one of the main biases in the comparison of primary frequency standard, and it could be a challenge for the forthcoming generation of atomic optical clocks. In this paper we report the evaluation of the gravitational redshift with respect to the Geoid reference at INRIM laboratories, with an accuracy of 1×10-17 in terms of relative frequency. The evaluation is based on GPS/levelling measurements and on the use of a local model for the Earth Geoid and its accuracy is limited by the reference potential of the Geoid

Low-Cost GNSS Solution for Continuous Monitoring of Slope Instabilities Applied to Madonna Del Sasso Sanctuary (NW Italy)

In recent years, the development of low-cost GNSS sensors allowed monitoring in a continuous way movement related to natural processes like landslides with increasing accuracy and limited eorts. In this work, we present the first results of an experimental low-cost GNSS continuous monitoring applied to an unstable slope aecting the Madonna del Sasso Sanctuary (NW Italy). The courtyard of Sanctuary is built on two unstable blocks delimited by a high cli. Previous studies and non-continuous monitoring showed that blocks suer a seasonal cycle of thermal expansion and a long-term trend to downslope a few millimeters (2/3) per year. The presence of a continuous monitoring solution could be an essential help to better understand the kinematics of unstable slope. Continuous monitoring could help to forecast a possible paroxysm phase that could end with a failure of the unstable area. The first year of experimental measurements shows a millimetric accuracy of low-cost GNSS, and the long-term trend is in agreement with other monitoring data. We also propose a methodological approach that considers the use of semi-automatized procedures for the identification of anomalous trends and a risk communication strategy. Pro and cons of the proposed methodology are also discussed