Ground deformation processes can be measured continuously with an accuracy down to millimetres and you don’t even need to be in the field, you can do it from space.
Ground movements include all geological or mining caused changes in the surface of the earth. Those movements can put a risk to people, buildings and infrastructures. Big changes caused by earthquakes can have catastrophic effects. But what about smaller, lurking changes?
Impacts of ground deformation
Even the smallest ground movements or deformations, which are not visible to the human eye, can have major consequences. For instance, damages to pipelines, dams or train tracks can be caused by changes of even a few millimeters. As a matter of fact, the smallest changes in the height of the topography are often first indicators of potentially catastrophic events such as landslides, dam bursts or derailments.
Additionally, about half of all train derailments are caused by bent or damaged rails (Liu et al. 2012). In the U.S. alone, there are an average of 3.7 derailments per day; in the EU there were 68 derailments in 2016 (Statista 2018). Such accidents not only lead to delays, train cancellations and increased operational costs, but can also become a danger to passengers.
Damage to oil or gas pipelines can be the cause of fires, explosions and environmental disasters, resulting in significant repair costs for operators. In addition, most pipeline companies have a zero tolerance policy, which is why preventing such incidents is of paramount importance to them.
Detection and Prevention
In order to detect ground deformation several methods exist. Yet, the most relevant are in-situ measurements and analyses based on satellite data. In-situ measurements are by far the most precise method. However, it is very costly and requires a lot of time and personnel to apply these on a large-scale.
Fortunately, earth observation satellites such as the Sentinel constellation continuously document the state of the Earth. Longer and more precise data collections lead to an improved detection in changes on the Earth’s surface by creating time series (Fig.1).
Thus, numerous geogenic as well as anthropogenically induced causes triggering ground movement processes can be investigated. With Sentinel 1 and accompanying radar missions, ground deformation can be detected on a millimeter scale by using different processing approaches. Thereby, areas where preventive and immediate actions are needed can be identified and disasters can be avoided.
One approach in the analysis of radar datasets is the monitoring of ground deformation processes based on Interferometric Synthetic-Aperture-Radar (InSAR). InSAR is a proven method for high-resolution detection of soil deformations and builds on the measurement of phase differences between two or more images of a region (Pepe & Calò 2017).
Since SAR data can be analyzed less dependent on the illumination and cloud cover of a scene compared to optical data, they have an advantage over optical images concerning the frequency of data availability.
Ground deformation poses a high risk to railways, pipelines and buildings, even changes on a millimeter scale can have large impacts. The detection of ground deformation processes in the field is cumbersome, which is why spaceborne data offers a great alternative as a data basis for ground motion analyses. Radar data are especially suitable for these and can even help to identify processes of a range of a few millimeters per year.
Liu, X., Saat, M. R., Barkan, C. P. L. (2012): Analysis of Causes of Major Train Derailments and Their Effect on Accident Rates. In: Transportation Research Record: Journal of the Transportation Research Board, No. 2289. S. 154-163
Pepe, A., Calò, F. (2017): A Review of Interferometric Synthetic Aperture RADAR (InSAR) Multi-Track Approaches for the Retrieval of Earth’s SUrface Displacements. In: Applied Sciences, 7, 1264. 39 S.
Statista (2018): Anzahl der Zugunglücke in der EU in den Jahren 2010 bis 2016 nach Unfallkategorie. https://de.statista.com/statistik/daten/studie/254053/umfrage/zugunfaelle-innerhalb-der-eu-nach-unfallkategorie/ (23.06.2020)