|Paper title||Literature trends of subsidence analysis using satellite interferometry|
|Form of presentation||Poster|
Subsidence is defined as gentle and graduate land surface lowering or collapse, which can be caused by either natural or anthropogenic activities. Land subsidence slowly proceeds due to sediment compaction under the pressure of overlying sediments. More intense motions in amplitude and time can be induced or worsened by human activity, such as groundwater withdrawal or underground mining.
Conventional geodetic measurement techniques have long been used for monitoring deformation processes. In particular, several methods including levelling, total station surveys, and GPS are still currently used for subsidence detection and monitoring. Nevertheless, these techniques are suitable only for local and site-specific analysis as they measure subsidence on a point-by-point basis, requiring a dense network of ground survey markers.
Space-borne radar interferometry approach allows measuring ground movement between two radar images acquired at different times on the same area, on a pixel-by-pixel basis. It is therefore remotely sensed, covering wide areas, quicker, and less labour intensive compared with conventional ground-based survey methods. More recently, radar interferometry rapidly growth and became a well-established Earth observation technique. The last decades witnessed a large exploitation of satellite InSAR (Interferometric Synthetic Aperture Radar) data.
The completeness of Web of Science (WoS) database was exploited to collect and critically review the current scientific state-of-the-art in the field of subsidence analysis using satellite InSAR in the last thirty years. From the pioneering work dating back to late nineties, the use of InSAR dramatically increased and thanks to the technological advances in terms of both acquisition sensors and processing algorithms, it is now possible to cover all the analysis of subsidence-related deformation at different stages, such as detection and mapping, monitoring and characterization, modelling and simulation.
This work is aimed to illustrate the role of satellite interferometry for subsidence analysis at a worldwide level over the last 20 years, highlighting current applications and future perspectives. From the WoS database original articles, book chapters, conference proceedings, and extended abstracts written in English and published by international journals after peer review where the authors exploited the InSAR technique to study subsidence were gathered. The data collection involved all contributions referring to every area in the world, looking for state by state. The data collection was operated in May 2021 and a final list of 766 contributions was retained. After the first skimming, each article was read and critically analysed in order to extract several information and identify the irrelevant contributions automatically extracted by the WoS database by the advanced search parameters. After this depth analysis, 73 contributions were further deleted by the list because they are related to volcanic systems, earthquakes or faults moving, or dam structures. In the end, the database was filled by the information extracted by 693 contributions.
Beside the general information about the selected contributions automatically downloaded from WoS (e.g., Publication Type, Authors and related affiliations, article Title, etc), it was necessary to insert new fields to catalogue the article to obtain a more detailed characterization:
- “CU” - Country Region of the authors;
- Area of Interest - localization of the study area investigated in the analysed work;
- SAR Satellite - list of the SAR satellite used to develop the investigation;
- Cause - list of the triggering factor of the subsidence as indicated in each contribution;
- Processing Technique - the processing technique adopted to retrieve ground deformation;
- Applications - the presented work were categorized according to the aim of the study
- Integration - the validation or integration, if any, with other data;
- Field evidences - the recording of damage on structure or ground.
The literature review highlighted that subsidence analysis covers 62 countries with at least one case study, by corresponding authors coming from 46 different nations. All the continents are covered, with the exception of Antarctica. The most represented country is China with 258 applications, followed by USA, Italy e Mexico with 59, 53 and 43 applications, respectively (Figure 1).
All the radar imagery archive were exploited to collect past and recent information on ground subsidence. The most used satellite platform turned out to be the C-band Envisat (counting 286 applications), followed by Sentinel-1 (154), ERS (153), L-band ALOS-1 (126), and X-band TerraSAR-X (95).
Concerning the image processing techniques adopted, either DInSAR (Differential InSAR) and InSAR algorithms were exploited, with 162 and 590 applications, respectively. Among the InSAR approaches SBAS (Small BAseline Subset) is represented by 187 case studies, PSInSAR (Persistent Scatterer Interferometry) is used in 146 circumstances while IPTA (Interferometric Point Target Analysis) is used within 36 contributions.
The triggering factors which resulted in land subsidence can be distinguished in two main groups, anthropogenic and natural. The first category counted 716 contributions, distributed mainly in groundwater exploitation (383), mining activities (137), urban loading (105), while in the second category the most represented factors are sediment compaction (117) and tectonic deformation (19).
Finally, the main aim of each contribution was identified and as a result 290 works dedicated to the monitoring of the subsidence phenomena, 171 devoted to the precise mapping of the extent of the vertical displacement and in 78 cases InSAR data were implemented for the modelling of the deformation were counted.
Therefore, satellite InSAR largely demonstrated to be highly valuable for subsidence studies in different setting and for different purposes, providing insights on slow-moving subsidence deformation mechanism. The upcoming European–wide EGMS (European Ground Motion Service), whose first baseline release is foreseen for the end of 2021, will represent a fundamental support for land subsidence analysis, providing a valuable flood of information regarding surface vertical deformation.