Monitoring land deformation in Changzhou city (China) with multi-band InSAR data sets from 2006 to 2012

Over exploitation of groundwater in Changzhou city, China can cause land deformation, which in turn proves detrimental to the urban infrastructure. In this study, multi-band synthetic aperture radar (SAR) data sets (C-band Envisat ASAR, L-band ALOS PALSAR, and X-band COSMO-SkyMed) acquired from 2006 to 2012 were analysed using the synthetic aperture radar (SAR) interferometry (InSAR) time-series method to investigate the relationship between spatial–temporal distribution of land deformation and groundwater exploitation. Annual deformation rate inferred from multi-band interferograms ranges from ?58 to 24 mm year^?1. Levelling-survey data were used to validate the multi-band InSAR measurements. The results showed that these two types of measurements were generally in agreement. Correlating groundwater-table and multi-band InSAR measurements at six groundwater-well stations showed that with the rise of the water table, the land rebounded. But in some areas with larger subsidence, continual subsidence was observed even though the water table rose after the prohibition of groundwater exploitation. This may have been caused by the hysteresis effect due to the consolidation of strata (especially for the creep deformation). Our study provides scientific evidence on the management of groundwater extraction and the assessment of land-subsidence hazards.     

The spatial and temporal subsidence variability of the East Mesa Geothermal Field,California, USA,and its potential impact on the All American Canal System

The spatiotemporal variability of subsidence around the East Mesa Geothermal Field (EMGF) near the All American Canal (AAC) has been measured using 30 temporally averaged interferograms from 1992 to 2000. Deformation rate maps from two shorter time periods indicated the maximum subsidence rate of the EMGF was reduced from??43 mm year^?1 (1992–1997) to??34 mm year^?1 (1996–2000) corresponding to decreasing net geothermal water production. The maximum subsidence on the East Highline Canal was??9.5 ± 0.5 and??2.4 ± 0.8 cm for each shorter time period. Interferometric synthetic aperture radar (InSAR) stacking demonstrated its utility in monitoring subsidence of the canal caused by the nearby geothermal plant at regional coverage superior to ground levelling networks. Such data on the subsidence of surface and subsurface hydrodynamics along the US–Mexico border are scarce, and are particularly significant in a zone of present and likely future acute water resource management sensitivity.     

Episodic ground deformation signals in Thessaly Plain (Greece) revealed by data mining of SAR interferometry time series

The Eastern Thessaly Plain presents an area of severe settlement phenomena, owing to the over-exploitation of the underground aquifer systems, causing significant damages to national infrastructures and private properties annually. Herein, both Persistent Scatterers (PS) and Small Baselines (SB) interferometric techniques were applied to study the history of ground deformation along the entire plain. Although the area consisted mostly of agricultural land, a sufficient number of point targets was obtained, well-distributed over the entire plain, permitting the recognition of spatial variations of the displacement field in addition to temporal trends. Our findings outline the southern part of the basin as the mostly affected area, whereas local subsidence patterns of lower magnitude were also recognized elsewhere. Episodes of significant ground subsidence, reaching several centimetres within a few months, characterize the deformation pattern of the area. Although average ground deformation rates do not exceed 2 cm year^?1, line-of-sight (LOS) displacements of up to 13 cm were observed, occurring during the summer–autumn periods. A geographic information system (GIS)-based post-processing approach for the analysis of synthetic aperture radar (SAR) time series is presented, by which these abrupt settlement episodes can be identified in both temporal and spatial domains. The analysis allows the separation between rapid subsidence phenomena during the summer–fall season and annual deformation rates, thereby providing valuable information regarding the actual deformation pattern of the area. The results confirm in situ geological observations, highlighting the unique behaviour of the area due to intense water pumping. The study underlines that average SAR displacement rate maps might be inadequate to describe complex deformation scenarios and could lead to misinterpretations. Exploitation of the full capacity of SAR time series by detailed examination of the displacement histories, through a tailored data-mining strategy, could provide valuable information to geotechnical engineers and planners.     

A study on measuring surface deformation of the L’Aquila region using the StaMPS technique

This research compares two time-series interferometric synthetic aperture radar (InSAR) methods, namely persistent scatterer SAR interferometry (PS-InSAR) and small baseline subset (SBAS) to retrieve the deformation signal from pixels with different scattering characteristics. These approaches are used to estimate the surface deformation in the L’Aquila region in Central Italy where an earthquake of magnitude Mw 6.3 occurred on 6 April 2009. Fourteen Environmental Satellite (ENVISAT) C-band Advanced Synthetic Aperture Radar (ASAR) images, covering the pre-seismic, co-seismic, and post-seismic period, are used for the study. Both the approaches effectively extract measurement pixels and show a similar deformation pattern in which the north-west and south-east regions with respect to the earthquake epicentre show movement in opposite directions. The analysis has revealed that the PS-InSAR method extracted more number of measurement points (21,103 pixels) as compared to the SBAS method (4886 pixels). A comparison of velocity estimates shows that out of 833 common pixels in both the methods, about 62% (517 pixels) have the mean velocity difference below 3 mm year^?1 and nearly 66% pixels have difference below 5 mm year^?1. It is concluded that StaMPS-based PS-InSAR method performs better in terms of extracting more number of measurement pixels and in the estimation of mean line of sight (LOS) velocity as compared to SBAS method.     

Estimation of land subsidence in deltaic areas through differential SAR interferometry: the Po River Delta case study (Northeast Italy)

ABSTRACT

River deltas are very complex environments vulnerable to flooding. Most of the world’s deltas are facing the immediate threat of land subsidence that jeopardizes the safety of millions of people worldwide. In Italy, the Po River Delta (PRD) (Northeast Italy) is an area historically affected by high rate of subsidence due to natural and anthropic factors. Even if the subsidence rates remarkably reduced during the last three decades, this process continues to be alarming in particular in low-lying sectors and along the coastline, where the loss of elevation, combined with the sea-level rise, increases the risk related to flooding. In this study, we monitored the subsidence affecting the entire PRD area with advanced differential interferometric synthetic aperture radar (A-DInSAR) techniques applied to three C-band SAR data sets acquired by the European Remote Sensing satellites, Environmental Satellite, and Sentinel-1A satellite in the last 25 years (from 1992 to 2017). The results of the interferometric processing, consisting of both mean velocity and displacement time series along the satellite line of sight, validated by comparison with levelling and global positioning system measurements, show increasing subsidence moving from the inland to the coastline, with maximum deformation velocities, for the most recent data, in the order of ?30 mm year^?1. In particular, many embankments near the coastal area are affected by high values of subsidence, which increase the flooding hazard of the entire deltaic territory. This work shows the importance of adopting A-DInSAR techniques to update the knowledge of the extent and rates of deformation of subsiding areas in low-lying territories such as river deltas. The outputs of such monitoring can be of primary importance for the future protection of the territory and the flooding risk mitigation.     

Integrated space geodesy for mapping land deformation over Choushui River Fluvial Plain,Taiwan

Groundwater is an important part of the precious water resources. As the fresh surface water resources become scarcer because of climate change, population growth, and industrial activities, more and more groundwater has been extracted to meet the demands of various water uses (e.g. municipal, industrial, and agricultural). Excessive groundwater extraction leads to severe ground subsidence which compromises the safety of surface and underground infrastructures. Modelling the effects of groundwater extraction is vital to the management and sustainable use of groundwater. However, results of such modelling have to be validated with inputs such as the field survey of ground subsidence. Levelling and continuous global positioning system (GPS) receiver networks are routinely used to collect these field measurements. Unfortunately, these techniques have limitations in terms of areal coverage and density of survey marks and, as a result, subsidence hot spots can be easily missed out. In order to provide a comprehensive picture of subsidence to aid geotechnical modelling and to assess the effectiveness of measures used to mitigate ground subsidence, satellite imaging radar interferometry techniques (interferometric synthetic aperture radar (InSAR) can be used to complement other deformation monitoring techniques. In this study, 20 Advanced Land Observing Satellite (ALOS) Phased Array L-band Synthetic Aperture Radar (PALSAR) images acquired from 31 December 2006 to 26 February 2011 were used to map the land displacement over the Choushui River Fluvial Plain (CRFP), Taiwan. The GPS measurements acquired at 10 continuously operating reference stations (CORS) were used to refine the orbit error in the each differential interferogram obtained from each radar image pair. The displacement time series over the distributed scatterers and the persistent scatterers were analysed. Several subsidence bowls were identified in CRFP. A quantitative comparison was conducted to compare the radar measurements to the GPS measurements over 36 GPS CORS stations. Good agreement between both measurements was observed with coefficient of determination (R²) of 0.97, absolute mean difference of 3.2 mm year^?1, and standard deviation of 4 mm year^?1. The InSAR-measured Line-of-Sight displacement and GPS-measured horizontal displacement were integrated to derive the vertical displacement map. Two displacement maps were generated using two ALOS-2 PALSAR-2 pairs acquired between 2015 and 2016. Similar subsidence patterns were found in the two maps compared to the 2006–2011 displacement rate map, suggesting the land over the same region might have continued to fall.     

Monitoring and analysis of mining 3D time-series deformation based on multi-track SAR data

Accurate monitoring of the developing process of a surface subsidence basin is the basis of building damage assessment and surface deformation prediction. In this paper, the Synthetic Aperture Radar (SAR) data of three different imaging geometries, TerraSAR, Radarsat-2, and Sentinel-1A, were exploited. Firstly, two-dimensional (2D) time-series deformation of the surface subsidence basin caused by 15,235 working face mining was obtained based on Multidimensional Small Baseline Subset (MSBAS) technology from 19 December 2015 to 5 March 2016. By comparing vertical deformation with levelling data, it is shown that the root-mean-square error of vertical deformation is 3.2 mm and the standard deviation is 1.9 mm when the ascending-descending track SAR data is available. Otherwise, the root-mean-square error of vertical deformation is 18.1 mm and the standard deviation is 11.6 mm. Because of the low precision of the north–south horizontal movement monitored by the SAR sensor, the vertical deformation acquired by MSBAS technology and the rules of the mining subsidence (horizontal movement is proportional to tilt) were combined to obtain the north–south horizontal movement which was proven to be reliable by comparing the 2D time-series deformation obtained by MSBAS technology. Then, the deformation of the railway in the surface subsidence basin was analysed based on the three-dimensional (3D) time-series deformation. The results show that the subsidence, tilt, and horizontal movement strongly influence the railway in the monitoring period, but will not affect the normal traffic. This experiment lays a technical foundation for preventing the occurrence of mining disasters and verifies the ability to monitor the deformation of buildings and structures by interferometry synthetic aperture radar technology.     

Advanced InSAR techniques for deformation studies and for simulating the PS-assisted calibration procedure of Sentinel-1 data: case study from Thessaloniki (Greece), based on the Envisat/ASAR archive

Using state-of-the-art InSAR techniques, namely persistent scatterers (PSs) and small baseline subset (SBAS) approaches, this study contributes to open geotechnical questions in the area of Thessaloniki (Greece) from a remote-sensing perspective. It also demonstrates the potential of these techniques for calibration purposes, with reference to the new C-band synthetic aperture radar (SAR) sensor on board the Sentinel-1 mission satellites. By exploiting the historical archive of Envisat/ASAR data, as well as a pair of the first Sentinel-1A SAR images, recent (2004–2010) deformation rates up to 18 mm year^–1 are detected over the study area. These results are then compared to the findings of previous InSAR and geophysical observations, indicating for example, subsidence or tectonic activity. On the other hand, the usefulness of the PS technique is shown over the same region for external SAR calibration purposes. This process simulates the PS-assisted calibration procedure to be applied systematically to Sentinel-1 SAR products.     

Combining differential SAR interferometry and the probability integral method for three-dimensional deformation monitoring of mining areas

With the exploitation of coal resources, ground surface subsidence continues to occur in mining areas, destroying the ecological environment and significantly affecting the daily productivity and life of humans. The differential synthetic aperture radar interferometry (D-InSAR) technique is widely used to monitor ground surface deformation because of its unique advantages such as high accuracy and wide coverage. However, conventional D-InSAR technology provides only one-dimensional (1D) displacement monitoring along the radar line of sight (LOS). This article proposes a method based on an analysis of the mining subsidence law for true three-dimensional (3D) displacement monitoring by combining D-InSAR and a subsidence prediction model based on the probability integral method. In this approach, 1D displacement, obtained using D-InSAR, is then combined with the prediction model to obtain the 3D displacement of ground surface target points. Here, 3D displacement curves were obtained for the Fengfeng mining area (China) using RadarSat-2 images obtained on 9 January and 2 February 2011. True ground surface displacement was measured simultaneously by levelling when the 152under31 s working face was being exploited in Jiulong mine. Vertical displacement and inclined deformation calculated using the proposed method were compared with levelling survey data and the results showed average differences of 3.2 mm and 0.1 mm m^?1, respectively; the calculated maximum displacement in the east–west and south–north directions were 106 and 73 mm, respectively. The spatial distribution of the displacements was in accordance with the mining subsidence law. Thus, the new method can retrieve highly accurate 3D displacements caused by mining subsidence.     

Surface deformation over the buried Nasr Abad salt diapir,Central Iran using interferometric synthetic aperture radar data

ABSTRACT

This study employs interferometric synthetic aperture radar (InSAR) data sets to monitor the surface deformation of the Nasr Abad buried salt diapir in the Central Basin of Iran. The Nasr Abad salt diapir is one of the largest buried salt diapirs in Iran and could be ideal site for oil/gas storage and industrial waste disposal. In this study, we use 40 advanced synthetic aperture radar (ASAR) images from Environmental Satellite (EnviSat) to analyse surface displacement rates of Nasr Abad diapir and its surrounding regions. A time series of line-of-sight (LOS) displacements on the residual cap above the buried diapir were obtained from both descending and ascending images between 2003 and 2010 by applying the Small-BAseline Subset (SBAS) technique. Tropospheric artefacts in the displacement interferograms were mitigated using the power-law correction method in Toolbox for Reducing Atmospheric InSAR Noise (TRAIN) software. Finally, the data for temperature, precipitation, and tidal forces were correlated with the time-series displacement results of four points that located on the residual cap. Our results indicate that surface above the diapir and an area of about 2 km² subsided with maximum LOS velocity of about 7 mm year^?1 for ascending images and 5 mm year^?1 for descending images. The amount of vertical subsidence derived from LOS decomposition in reactive stage of Nasr Abad salt body is about 7 mm year^?1. Comparing the temperature and precipitation data with the time series of displacement confirmed that the salt expands when temperatures increases and that salt flow accelerates when it is wet. The displacement pattern retrieved from InSAR analysis is in good agreement with intervals near maximum and minimum solid earth tides. Monitoring the activities of the Nasr Abad region over 7 years shows that the region of surface subsidence is confined to the area along the Khurabad and AbShirin-Shurab Fault zones in the southern Central Basin.     

An approach for accurately retrieving the vertical deformation component from two-track InSAR measurements

As is well known, both conventional differential synthetic aperture radar interferometry (D-InSAR) and multi-temporal synthetic aperture radar interferometry (MT-InSAR) have a common limitation that they only can measure the deformation component along the radar line of sight (LOS) direction. However, in the majority of disaster investigations, there is more interest in the vertical deformation component than that of the horizontal direction, for example, in measuring ground subsidence in urban areas, or ground subsidence due to underground mining. To estimate the vertical deformation component accurately, it is in theory necessary to create at least three independent equations, and solve the vertical, the North–South, and the East–West deformation components by exploiting at least three-track InSAR LOS measurements or combining at least two-track InSAR LOS measurements with azimuth measurements. However, these methods are greatly limited and sometimes not even practical because there is typically little chance of obtaining a three-track SAR data set covering the same area in the same time span, and the accuracy of the azimuth measurements is far lower than that of InSAR LOS measurements. In this article, we found that it is possible to solve for the vertical deformation component from two-track InSAR LOS measurements in some circumstances. Then, an approach for accurately retrieving the vertical deformation component from two-track InSAR LOS measurements is proposed, and the analytical expression is presented. The approach is illustrated through an investigation of the ground subsidence in an area of Beijing, China. Unlike previous methods, this approach can accurately retrieve the vertical deformation component from two-track InSAR LOS measurements, and provide more reliable results for improving the interpretation of ground subsidence phenomena.     

Characterization and causes of land subsidence in Beijing,China

Long-term overexploitation of groundwater is the primary factor causing regional land subsidence in the Beijing plain area, China. Currently, large subsidence funnels exist, one each in southern and northern Beijing. We adopted the multi-temporal interferometric synthetic aperture radar (MT-InSAR) method, incorporating both persistent scatterer (PS) and small baseline (SB) approaches on 47 Envisat Advanced Synthetic Aperture Radar (ASAR) single look complex (SLC) images to map land subsidence in the Beijing plain area. The temporal and spatial variations of land subsidence and its seasonal variation were explained by the MT-InSAR results. Then, the InSAR results were combined with the dynamic monitoring of groundwater level, extensometer measurements, and hydrogeological data; the characterization and causes of land subsidence were analysed with Geographic Information System (GIS) spatial analysis methods. The results show the following. 1) Land subsidence developed rapidly in the Beijing plain area from 2003 to 2010, with obviously uneven settlement; settlement rates exceeded 100 mm year^?1 in some areas. Seasonal variation in settlement rates may be affected by changes in the precipitation rates and the exploitation of groundwater. 2) The contribution of different aquifer systems to land subsidence varies. The variation in the groundwater level in the second confined aquifer, at a depth of 100–180 m, has the greatest impact on land subsidence. 3) The settlement is centred in the lower part of the Wenyu–Chaobai and Yongding alluvial fan areas, where the compressible layer is more than 100 m thick. Meanwhile, land subsidence forms a structural feature with larger differences in the deformation gradient on both sides of faults.     

Monitoring of recent ground surface subsidence in the Cangzhou region by the use of the InSAR time-series technique with multi-orbit Sentinel-1 TOPS imagery

ABSTRACT

By collecting 39 scenes of descending images and 26 scenes of ascending images of Sentinel-1 synthetic aperture radar (SAR), we monitored the ground subsidence situation of Cangzhou in China during the period from March 2015 to February 2017 with the advanced synthetic aperture radar interferometry (InSAR) time-series technique and obtained the time-series subsidence rates of Cangzhou. We then selected the two sets of results of the monitoring obtained during the same period (from July 2015 to December 2016) to verify the results’ accuracy, considering three overlapping areas (Xinhua District, Botou County, and Dongguang County). This analysis clearly indicated that both types of results have good consistency, and the maximum subsidence occurred in Dongguang County. By further study of the central area of Dongguang and the related urban development, we found that the subsidence reached about 80.0 mm over the study period and there was a close relationship between the subsidence trend and the main direction of the city development. Moreover, by combining the two sets of results, we confirmed that there has been subsidence of the high-speed railway line in the whole of the Cangzhou area, among which the most obvious subsidence has occurred in Dongguang and Qing Counties. Finally, it was proved that the Sentinel-1 data can be used to monitor ground surface subsidence, and the data are especially effective in identifying persistent scatterer points along a linear feature. Therefore, this article could provide reliable data to assist with important decisions about urban development projects in the Cangzhou area in the next few years.     

Two‐scale surface deformation analysis using the SBAS‐DInSAR technique: a case study of the city of Rome,Italy

We have exploited the capability of the differential synthetic aperture radar (SAR) interferometry (DInSAR) technique, referred to as Small BAseline Subset (SBAS) approach, to analyse surface deformation at two distinct spatial scales: a low resolution, large scale, and a fine resolution, local scale. At the large scale, the technique investigates DInSAR data with a ground resolution of the order of 100 m×100 m and leads to generate mean deformation velocity maps and associated time series for areas extending to some thousands of square kilometres. At the local scale, the technique exploits the SAR images at full spatial resolution (typically of the order of 5 m×20 m), detecting and analysing localized deformation phenomena. The study is focused on the city of Rome, Italy, and we used the ERS‐1/2 satellite radar data relevant to the 1995–2000 time period. The presented results demonstrate the capability of the SBAS approach to retrieve, from the low‐resolution DInSAR data, large‐scale deformation information leading to identify several sites affected by significant displacements. Our analysis permitted us to conclude that a major contribution to the detected displacements is due to the consolidation of the alluvial soils present in the area, mostly enforced by the buildings' overload. Furthermore, in a selected area, a detailed analysis was carried out by exploiting the full resolution DInSAR data. In this case we investigated deformation phenomena at the scale of single buildings. As key result we showed that differential displacements of few mm a^?1, affecting single man‐made structures or building complexes, could be detected, thus allowing to identify sites that may potentially be involved in critical situations.     

Reduced rate of land subsidence since 2016 in Beijing,China: evidence from Tomo-PSInSAR using RadarSAT-2 and Sentinel-1 datasets

ABSTRACT

Land subsidence associated with groundwater extraction in the city of Beijing, China, has been a problem for decades. Remote sensing has been used extensively in prior studies to monitor subsidence in Beijing. However, given recent changes in precipitation and groundwater management, there is an urgent need to update the subsidence record and to evaluate whether the long-term spatiotemporal patterns of subsidence have changed. This study therefore investigates the recent spatiotemporal patterns of land subsidence in Beijing by tomography-based persistent scatterer interferometry SAR (Tomo-PSInSAR) technology, using 39 RadarSAT-2 images from 2012 to 2015 and 33 Sentinel-1 images from 2016 to May-2018, and drawing upon Geographic Information System (GIS) spatial analysis methods. Vertical ground deformation rates in Beijing were found to range from ?176.2 to +12.3 mm year^?1 from 2012 to 2015, but subsequently decreased to ?119 to +8 mm year^?1 from 2016 to May 2018. Three spatial scale of subsidences are evident: At the metropolitan regional-scale, the total area of subsidence area is about 1235.2 km², and comprises four main subsiding regions, located in the northern and eastern parts of the city. More than 85% of the subsiding area is located between the Fifth and Sixth Ring Roads. At a more local scale, eight main subsidence bowls are characterized by different patterns of subsidence. Some of the subsidence bowls are separated by active faults. Time-series data of the displacement show that the decreasing subsidence rate after 2016 could be due to the 1 m rise in mean groundwater level from the end of 2014 to mid-2018. This change in groundwater level is likely due to an increase in precipitation since 2016, and water transfers, which reached 2.3 × 10⁹ m³ by 2017 from the South-North Water Transfer Project. At the scale of individual infrastructure projects, the Beijing subway, main roads and the Capital Airport all show severe uneven subsidence, which is a cause for concern. To our knowledge, this research is the first study using satellite SAR remote sensing methods to document the change in the land subsidence rate of Beijing. Starting in 2016, the rate notably declined, suggesting that subsidence mitigation strategies are beginning to have an effect.     

Glacier elevation changes (2012–2016) of the Puruogangri Ice Field on the Tibetan Plateau derived from bi-temporal TanDEM-X InSAR data

This study aims to evaluate the potential of TerraSAR-X (TSX) add-on for Digital Elevation Measurement (TanDEM-X) bi-static synthetic aperture radar (SAR) data sets for the retrieval of glacier digital elevation models (DEMs) and elevation changes over mountain regions. We exploited two pairs of TanDEM-X SAR data sets acquired in 2012 and 2016 over the Puruogangri Ice Field (PIF), which is the largest modern glacier on the Tibetan Plateau (TP). Two fine-detail and high-precision DEMs for 2012 and 2016 over the PIF were generated by differential interferometric processing, and were validated against height measurements from global positioning system (GPS) and Ice, Cloud, and land Elevation Satellite (ICESat) altimetry, yielding a vertical accuracy of 1.91 ± 0.76 m and 1.69 ± 0.83 m, respectively. The elevation changes were derived by differencing the bi-temporal TanDEM-X DEMs and revealed predominant glacier surface thinning on the PIF. An annual surface thinning rate of ?0.317 ± 0.027 m year^?1 was estimated in the period 2012–2016, which is much larger than the estimate of ?0.049 ± 0.200 m year^?1 for the period 2000–2012 reported in previous studies. This accelerating trend of glacier surface thinning might be attributable to the continued increase in summer temperature since the 1980s and decrease in annual precipitation between two periods of investigation. This study demonstrates that comparison of the bi-temporal TanDEM-X DEMs is an efficient method for accurate and detailed retrieval of the latest surface elevation changes of mountain glaciers.     

InSAR time-series analysis of land subsidence in Bangkok,Thailand

Land subsidence poses a serious risk to the low-lying coastal city of Bangkok, Thailand; major flooding occurred there in 1983 and again in 2011. Extreme water pumping in the past led to subsidence rates of up to 120 mm year^?1. Although water extraction is now controlled, maximum rates measured by levelling today are still up to 20 mm year^?1. In this study, we apply interferometric synthetic aperture radar (InSAR) time-series analysis to study subsidence in Bangkok between October 2005 and March 2010. We validate the InSAR results, by comparing levelling rates and find good agreement between the two techniques. We detect approximately 300,000 coherent pixels overall, with an average density of 120 observations per km². This is two orders of magnitude greater than the density of levelling benchmarks and reveals subsiding areas that are missed by the levelling network.     

Joint approach using satellite techniques for slope instability detection and monitoring

A joint approach using satellite techniques was applied to two different regions (Sellas and Chalkeio villages) of Peloponissos (Greece) in order to detect and monitor slope instability. In the context of the research effort, a GPS campaign network, along with one permanent GPS station and a corner reflector (CR) network, was established at each region. From the two GPS campaigns that were carried out, ground displacements in the north and east components for Sellas region reached a magnitude of 9 and 8 mm, respectively, whereas for Chalkeio they were of the order of 1 cm and 8 mm, respectively. These results, however, are still preliminary and need validation from additional GPS campaigns that are planned to be carried out in future. The temporal resolution provided by the position time series of the permanent GPS stations highlighted the main features of both instability phenomena, that is, sensitivity at both horizontal components of motion for the Sellas region and slow linear trends for the Chalkeio region. The achieved precision of the daily solutions for both permanent GPS stations was found to be 1–3 mm for the horizontal components and 5–8 mm for the vertical components. Regarding the preliminary study of differential synthetic aperture radar (SAR) interferometry (DInSAR) in CR network, each reflector has been identified in SAR imagery, but at present the volume of SAR acquisitions is not adequate for providing safe deformation and error estimations. On the other hand, the permanent scatterers interferometry and small baselines subset (SBAS) techniques revealed a discontinuity in retrospective deformation rate along the observed rupture of Chalkeio village of almost 6 mm year^?1.     

Integration of TerraSAR-X and PALSAR PSI for detecting ground deformation

In connection with the detection of various spatial- and temporal-scale ground settlements, an integrated persistent scatterer interferometry (PSI) approach is discussed using multi-source, multi-temporal, and multi-resolution synthetic aperture radar (SAR) data. Based on the comprehensive analysis of characteristics of available radar sensors, two remote-sensing SAR data sets were selected: 1 m resolution X-band TerraSAR-X and 10 m resolution L-band Advanced Land Observing Satellite (ALOS) phased array L-band SAR. ‘Tianjin Binhai New Area’ has become one of the most important economic centres in China, and one of its fast-developing urban areas, Tanggu, was selected as the study area. PSI processing was conducted on both data sets. Substantial validation was performed for PSI results from both data sources using levelling measurement. The overall good agreement confirmed the ground deformation maps derived from both data sets. Integration of PSI results appears to be a potentially significant contribution to solving the problems related to common spatial and temporal gaps when using single-type data sets. Application of both data sets revealed the capability of integrated PSIs to measure ground deformation with strong temporal and spatial variation, thereby improving the interpretation of ground deformation characteristics which increases the confidence of hazard assessment and provides some insight into complex underlying mechanisms.     

SAR-derived wind fields at the coastal region in the East/Japan Sea and relation to coastal upwelling

The relationship between the modification of synthetic aperture radar (SAR) wind field and coastal upwelling was investigated using high-resolution wind fields from Advanced Land Observing Satellite (ALOS) Phased Array type L-band synthetic aperture radar (PALSAR) imagery and sea-surface temperature (SST) from National Oceanic and Atmospheric Administration/Advanced Very-High-Resolution Radiometer (NOAA/AVHRR) data. The retrieved SAR wind speeds seem to agree well with in situ buoy measurements with only a relatively small error of 0.7 m s^?1. The SAR wind fields retrieved from the east coast of Korea in August 2007 revealed a spatial distinction between near and offshore regions. Low wind speeds of less than 3 m s^?1 were associated with cold water regions with dominant coastal upwelling. Time series of in situ measurements of both wind speed and water temperature indicated that the upwelling was induced by the wind field. The low wind field from SAR was mainly induced by changes in atmospheric stability due to air–sea temperature differences. In addition, wind speed magnitude showed a positive correlation with the difference between SST and air temperature (R² = 0.63). The dependence of viscosity of water on radar backscattering at the present upwelling region was negligible since SAR data showed a relatively large backscattering attenuation to an SST ratio of 1.2 dB °C^?1. This study also addressed the important role of coastal upwelling on biological bloom under oligotrophic environments during summer.