4D Monitoring of Active Sinkholes with a Terrestrial Laser Scanner (TLS): A Case Study in the Evaporite Karst of the Ebro Valley, NE Spain

Abstract

This work explores, for the first time, the application of a Terrestrial Laser Scanner (TLS) and a comparison of point clouds in the 4D monitoring of active sinkholes. The approach is tested in three highly-active sinkholes related to the dissolution of salt-bearing evaporites overlain by unconsolidated alluvium. The sinkholes are located in urbanized areas and have caused severe damage to critical infrastructure (flood-control dike, a major highway). The 3D displacement models derived from the comparison of point clouds with exceptionally high spatial resolution allow complex spatial and temporal subsidence patterns within one of the sinkholes to be resolved. Detected changes in the subsidence activity (e.g., sinkhole expansion, translation of the maximum subsidence zone, development of incipient secondary collapses) are related to potential controlling factors such as floods, water table changes or remedial measures. In contrast, with detailed mapping and high-precision leveling, the displacement models, covering a relatively short time span of around 6 months, do not capture the subtle subsidence (<0.6-1 cm) that affects the marginal zones of the sinkholes, precluding precise mapping of the edges of the subsidence areas. However, the performance of TLS can be adversely affected by some methodological limitations and local conditions: (1) limited accuracy in large investigation areas that require the acquisition of a high number of scans, increasing the registration error; (2) surface changes unrelated to sinkhole activity (e.g., vegetation, loose material); (3) traffic-related vibrations and wind blast that affect the stability of the scanner.

Inventory data on the sinkhole occurrences from Proterozoic Cuddapah Basin, India

“…From the Review of literature it is clear that, there is a remarkable raise in investigations on sinkhole and associated damages on a global scale during the last two decades [5], [6]. A comprehensive sinkhole inventory is the primary aspect in Sinkhole hazard analysis and risk assessment.…”

The Role of Earth Observation, with a Focus on SAR Interferometry, for Sinkhole Hazard Assessment

“…Earth observation technologies are used for compiling sinkhole inventories but also have the potential to be more widely used for assessing sinkhole damage [44]. This includes the monitoring of active sinkholes [45] and even to identify environmental risk factors that can contribute to sinkhole development. Remote sensing is often used to assess the extent and magnitude of infrastructure damage using techniques involving high-resolution change detection on optical or SAR imagery before and after the event [44].…”

“…It has successfully been used after disasters such as earthquakes [44], volcanic eruptions [46] and landslides [47] and could therefore also be applied to sinkhole events. Remote sensing can also be used to monitor the evolution of active sinkholes, this requires very high-resolution data and airborne LiDAR has been shown to be an effective tool [45].…”

“…Various remote sensing platforms are used for sinkhole inventories, each with its own advantages and disadvantages. Ground-based systems such as ground-based radar and portable LiDAR are typically cost-effective and offer good resolution; however, they do not cover large areas, can easily be obstructed and it is challenging to keep the sensor stable over long periods [26,45]. Optical or LiDAR sensors flown on airborne platforms are well suited for sinkhole investigations due to their high resolution [62,63].…”

“…Terrain models can be generated from many sources with the simplest being topographic maps generated by surveying techniques. Remote sensing techniques to generate terrain models include terrestrial airborne laser scanning [45,62,69], stereo-photogrammetry using optical imagery [70], drone-based Structure from Motion (SfM) [71] and SAR interferometry [72,73] among others. Global elevation models such as the SRTM and ASTER GDEM, generated through spaceborne SAR interferometry or stereo-photogrammetry respectively, are freely available.…”