Conference Agenda

Landslides are destructive geohazards to people and infrastructure, resulting in hundreds of deaths and billions of dollars of damage every year. Therefore, mapping the rate of accumulation of such geohazards and understanding their mechanics is of paramount importance to mitigate the resulting impacts and properly manage the associated risks. In this mid-term project report, the main outcomes relevant to the joint European Space Agency (ESA) and the Chinese Ministry of Science and Technology (MOST) Dragon-5 initiative cooperation project ID 59339 “Earth observation for seismic hazard assessment and landslide early warning system” are reported. The primary goals of the project are to further develop advanced SAR and optical techniques to investigate seismic hazard and risk, detect potential landslides on wide regions, and demonstrate EO-based landslide early warning system over selected landslides. Regarding the landslide hazard, in order to achieve these objectives, next tasks were developed up to now: a) a procedure for phase unwrapping errors and tropospheric delay correction; b) improvement of a cross-platform SAR offset tracking method for the retrieval of ground displacements; c) InSAR and PolInSAR monitoring and semiautomatic mapping of active displacement areas on wide regions, identification of triggering factors and modelling; d) application of InSAR-based landslide early warning system on selected sites. The achieved results, which mainly focus on selected sensitive regions including the Tibet Plateau and the Three Gorges in China and the Alcoy valley in Spain, provide essential assets for planning present and future scientific activities devoted to monitoring landslides. These analyses are crucial for an optimal prevention and management of these geohazards, as well as for a rapid response after their occurrence.

In the framework of Dragon-5 project, Northeastern University (NEU) from China and the National Institute of Geophysics and Volcanology (INGV) from Italy analyzed the multiple geohazards over the heavy industrial base in Northeast China using time Series SAR images. Moreover, we have also considered a new study site, the Changbaishan active volcano (Jilin Province, ~300 km east from Shenyang). This volcano last erupted in 1903 and was responsible for the largest eruption of the last millennium in 946 CE. Changbaishan is affected by landslides, earthquakes, degassing, and ground deformation. Deformations occurred during the 2002-2006 unrest episode and in 2017, when a nuclear test in North Korea triggered landslides. The multi-hazard exposure of Changbaishan is relevant because a population of ~135000 in China and 31000 in North Korea lives within 50 km from the volcano. We analyze the Changbaishan 2018–2020 deformations by using remote sensing data and detect an up to 20 mm/yr, NW-SE elongated, Line of Sight movement on the southeastern flank and a −20 mm/yr Line of Sight movement on the southwestern flank.

These data reveal an unrest occurring during 2018–2020. Modeling results suggest that three active sources are responsible for the observed ground velocities: a deep tabular deflating source, a shallower inflating NW-SE elongated spheroid source, and a NW-SE striking dip-slip fault. The depth and geometry of the inferred sources are consistent with independent petrological and geophysical data. Our results reveal an upward magma migration from 14 to 7.7 km. The modeling of the leveling data of the 2002–2005 uplift and 2009–2011 subsidence depicts sources consistent with those responsible for the 2018–2020 unrest. The past uplift is interpreted as related to pressurization of the upper portion of a spheroid magma chamber, whereas the subsidence is consistent with the crystallization of its floor, this latter reactivated in 2018–2020. Therefore, Changbaishan is affected by an active magma recharge reactivating a NW-SE striking fault system.

The analysis and modelling of the Changbaishan volcano has been the topic of a joint published paper on Frontiers in Earth Sciences (doi: 10.3389/feart.2021.741287).

Concerning the Fushun open pit mine, in these first 2 years of the project, the 2 research teams have collaborated to following the MT-InSAR processing updating the results from DRAGON-4 project until the end of 2021. We have also performed new processing technique as the OT time series analysis during 2013 to 2016 for this area.

Fushun west Opencast coal mine (FWOCM), located in the southwest of Fushun city, China, is the largest opencast mine in Asia. Since the 1920s, more than 90 landslides have been reported in FWOCM, especially the huge landslide on the south slope, which named Qiantaishan landslide. The Qiantaishan landslide has experienced a fast moving period during 2013 to 2016, and has stabilized since 2017. During the fast moving period, the landslide mass has moved approximately 90 meters. However, since 2017, displacements of the Qiantaishan landslide is less than 150 millimeters per year. In order to analyze the spatial pattern and temporal evolution of different periods of the Qiantaishan landslide, both MT-InSAR and multi-temporal pixel offset tracking has been conducted. Multi-temporal pixel offset tracking is conducted based on 53 Cosmo SkyMed SAR images collected from 2013-07-03 to 2016-12-18, to monitor displacement of the fast moving period of Qiantaishan landslide. The results show that the landslide moves very fast during 2014, and slows down during 2015 to 2016. Besides, displacement of the Qiantaishan landslide shows very strong correlation with precipitation, which accelerates in rainy season and decelerates in dry season. Starting from the beginning of 2017, the Qiantianshan landslide gradually stabilized. The MT-InSAR analysis is conducted based on Sentinel-1 images collected during 2017-01-11 to 2021-12-16, to monitor the slow-moving period of Qiantaishan landslide. The MT-InSAR results show that the displacements rate of the Qiantaishan landslide is within 150 mm/year, which has basically stabilized. The area with the largest displacement is located near the former Liushan old river channel, and the maximum displacement rate is approximately 120mm/yr. This is due to the undercutting of the bedrock near the old river channel and the existence of river pebble layer, which has good permeability, allowing rainwater to penetrate through the cracks on the slope, reducing the tensile strength and increasing the mobility of the landslide body.

With the key goal to exploit satellite Synthetic Aperture Radar (SAR) imagery and advanced processing methods for archaeological prospection and heritage sites protection, the Dragon-5 SARchaeology international collaboration project is making step changes to demonstrate the capability of SAR to detect objects of archaeological significance, and monitor the status and stability of cultural and natural heritage sites and their assets. These are Earth observation applications of paramount importance in the field of land monitoring and Earth system science. The project focuses on a range of study sites in China, Russia, Mongolia, Italy, Norway and Bulgaria, including a wealth of heritage asset types, namely burial mounds, partly buried archaeological ruins, standing monuments within urban centres, natural reserves, paleo-channels and ice patches with organic remains.

This work reports on the key achievements from the first two years of the project, during which the research activities focused on: state-of-the-art review of heritage applications of imaging radar; multi-sensor SAR and optical data collection and tailored tasking of new acquisition campaigns over the study sites; SAR image processing with feature extraction, image classification, change detection and Interferometric SAR (InSAR) methods; analysis and interpretation; field data collection, ground truthing and validation of EO-based evidence and observations.

In the wider Province of Rome (Italy), a long-term InSAR ground deformation analysis was carried out with big data stacks of Sentinel-1 IW SAR imagery, and land subsidence hotspots that may represent a potential threat to heritage assets were identified. An initial investigation on the detectability of buried archaeological features was also performed across sub-urban and rural landscapes of the province by analysing multi-frequency SAR data collected in C-band in RADARSAT-2 Fine Beam and Sentinel-1 IW dual-pol. and in X-band by COSMO-SkyMed. The interpretation of SAR imagery has been aided by very high resolution optical data from DEIMOS-2, WorldView-3, Pléiades-1 and Google Earth, and validated by evidence collected in the field.

In Wuhan (China) long-term SAR and InSAR analyses were carried out to estimate risks for local cultural heritage sites due to urbanization and surface motion. Long time series of COSMO-SkyMed data, acquired via the Wuhan-CSK project – a cooperation between Wuhan University and the Italian Space Agency (ASI) – as well as TerraSAR-X data were used for long-term deformation estimation and to survey the urbanization development. Additionally, ERS-1/2 and ENVISAT ASAR data acquired via the Dragon-5 project were processed. The available historical data from Keyhole sensors allowed for manual mapping of the urban areas into the mid-1960s. The 3D development of the urban area was in the focus of the processing of high resolution SAR data, so that the detailed 2D and 3D urbanization analysis allowed for identification of the urban development and therefore a better risk assessment for cultural heritage sites in Wuhan.

For the research on burial mounds, the work focused on improving the methodologies and better monitoring the sites with respect to climatological factors. This is important as the most valuable burial mounds are to be found in or close to permafrost areas. Global warming and thawing of permafrost endanger the organic remains in some of the sites in question that are currently still frozen and therefore extremely valuable for archaeological analysis. Learning more about the current extent of permafrost, monitoring spatial changes and hopefully being able to predict the spatio-temporal patterns of future changes is of crucial importance for the planning and prioritization of future archaeological excavations.

The detection of looting activities is an important task for cultural heritage protection. SAR interferometric coherence is a very sensitive change detection tool and, in combination with the high temporal availability of SAR data, could make for a good approach of looting detection. The main challenge is the very high sensitivity of the coherence to change and other factors, such as soil moisture and spatial baseline differences. Successful change detection with low false alarm rates is therefore difficult, especially when looking for changes in sub-pixel dimensions. To test new approaches based on detecting statistical inhomogeneities within adaptive local and non-local neighbourhoods, a test is prepared at the satellite receiving station of LIESMARS, Wuhan University. On the test site, looting structures will be artificially created to conduct tests of detectability and support method development using high resolution TerraSAR-X data and medium resolution Sentinel-1 data.