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.     

Ground deformation due to tectonic, hydrothermal, gravity, hydrogeological, and anthropic processes in the Campania Region (Southern Italy) from Permanent Scatterers Synthetic Aperture Radar Interferometry

We apply the Permanent Scatterers Synthetic Aperture Radar Interferometry (PS-InSAR) technique to the Campania Region (Southern Italy), which includes the Southern Apennines chain and Plio-Quaternary structural depressions, with the aim to detect ground displacements at a regional scale. The study area, which extends for 13,600 km², is characterized by intense urbanization, active volcanoes (Phlegraean Fields, Vesuvius and Ischia), seismogenic structures, landslides, hydrogeological instability. PS-InSAR technique allows us to identify a set of radar benchmarks (PS) where accurate displacement measurements can be carried out. About 1.7·10⁶ PS are identified by processing Synthetic Aperture Radar (SAR) images acquired in ascending and descending orbits from 1992 to 2001 by the European Remote Sensing satellites (ERS). The PS-InSAR application at regional scale detected ground deformations ranging from + 28 to − 39 mm/yr. The calculated velocity values are consistent with the available GPS and levelling data from selected areas. We identify volcanic areas in which the deformation is mainly related to the depressurization of the local hydrothermal systems, and recognize deformations along seismogenic and aseismic NNW-SSE and NW-SE faults. The deformations localized along the Southern Apennines chain are mainly related to landslides while those occurring in the plains are due to subsidence processes induced by intensive drainage from wells, i.e. anthropic activity. The review of 9 years of SAR data shows that tectonic, volcanic/hydrothermal, gravity, and anthropic processes are responsible for the ground deformation of Campania. The proposed joint interpretation of deformation fields related to natural and anthopogenic factors provides a comprehensive view of the dynamics of the Earth’s surface.     

青藏铁路冻土监测无线传感器网络节点设计

着眼于对青藏铁路沿线多年冻土区典型段地温进行自动监测,并将所检测的数据传入监控中心,与其它有关信息综合分析、处理,设计了基于无线传感器网络WSN(wireless sensor networks)的青藏铁路冻土温度自动监测系统。该节点以CC2430为核心,通过温度传感器DS18B20对青藏铁路冻土温度进行监测。由其构成的WSN可为千里青藏铁路冻土区的安全运营和养护维修提供及时、有效、准确的监测数据,并对铁路长期运营、维修和养护提供科学依据。     

青藏铁路综合安全实时监测平台技术方案研究

分析了在青藏铁路特殊环境下综合安全实时监测平台应具备的功能,构建了该平台的体系架构.分析了平台对于实时数据的闭环处置流程,给出了平台建设的技术实现要点.综合安全实时监测平台的建设将为青藏铁路公司各相关部门或领导建立一个综合性的全面的公司运营安全情况视图,为领导的决策、安全管理及综合性维护等提供依据.将形成较为完整的铁路运营安全保障体系,实现对各类安全监控信息资源的综合、高效利用,填补高原铁路综合监控技术的空白.     

基于WSN的青藏铁路温度监测系统研究

无线传感器网络综合了传感技术、MEMS技术、无线通信技术和分布式信息处理技术等,能够通过各类集成化的微型传感器,实时、全方位地监测被测对象的信息,通过嵌入式系统对信息进行处理,并通过自组织无线通信网络,以多跳中继方式将所感知信息传送到终端。利用无线传感器网络可以很好地实现对青藏铁路冻土区的无人实时监测和无线数据传输,可以对冻土区铁路工程进行长期、全面、系统的观测,确保青藏铁路安全运营,并对铁路长期运营、维修和养护提供科学依据。     

The present status of subsiding land vulnerable to roof collapse in the Jharia Coalfield,India, as obtained from shorter temporal baseline C-band DInSAR by smaller spatial subset unwrapped phase profiling

In this paper, we identified recently subsiding areas in Jharia Coalfield, Jharkhand, India from the shorter temporal baseline Radarsat-2 C-band interferometric synthetic aperture radar (InSAR) data pairs of 2012. Although shorter wavelength C-band differential InSAR (DInSAR) is more sensitive to slow deformation and better suited for higher precision land subsidence measurement, the dynamic and adverse land cover in mining areas and resulting temporal decorrelation problem poses a serious problem for DInSAR observation in mining areas. We used smaller temporal baseline data pairs and adopted InSAR coherence-guided incremental filtering with smaller moving windows to highlight the deformation fringes over temporal decorrelation noise. We identified the deformation fringes and validated them based on ground information to prepare the land subsidence map of the coalfield in 2012. Several new, previously unreported subsidence areas were detected in the present study with a total subsiding area of 6.9 km². The recent incidence of roof collapse on 15 November 2014 at Angar Patra village in Katras region of the coalfield where 45 houses collapsed and 10 people were injured is situated in a highly subsiding vulnerable area as obtained from the present study. Due to spatial discontinuities of InSAR coherence, DInSAR phase unwrapping for the entire study area in one go did not appear feasible. To avoid this problem, we performed DInSAR processing in smaller spatial subsets and unwrapping of the subset interferograms by a ‘minimum cost flow’ algorithm. Subsequently, we plotted unwrapped phase profiles across the deformation fringes and retrieved the maximum deformation phase with respect to background phase and translated them into radar line of sight (LOS) displacement rates. For obtaining the average subsidence rates, we adopted InSAR coherence-weighted LOS displacement rates taking into account the contribution of each data pair as a function of DInSAR phase quality of the fringe areas. Ground-based subsidence measurements by precision levelling were conducted in four test sites that had been undergoing active underground mining during the observation period. We compared space-borne DInSAR-based subsidence rates obtained by the adopted technique with precision levelling measurements. Overall, the results are found to agree well. In the four test sites with gentle to flat topography, land subsidence occurs at slow to moderate rates due to compression of in-filled material (resulting from sand stowing in underground mining), without any evidence of roof collapse. In such cases, the horizontal displacement component is less significant, and overall surface displacement occurs essentially in the vertical direction. However, we assessed the nature of subtle horizontal strain to infer relative shrinkage or dilation of the land surface which could be additive or subtractive to vertical displacement in DInSAR-based LOS displacement.     

DInSAR技术的最新进展

从传统合成孔径雷达差分干涉测量(DInSAR)技术面临的问题出发,分析了近年来DInSAR技术发展的新趋势,详细论述了最小二乘(Least Squares,LS)方法、永久散射体(Permanent Scatterer,PS)方法和小基线集(Small Baseline Subset,SBAS)方法的原理、应用及发展趋势。     

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.     

青藏高原多年冻土本底调查信息系统

全面系统了解青藏高原多年冻土本底资源,对青藏高原多年冻土科学研究有重要意义,也为工程建设、资源开发、生态和环境保护提供基础性科学数据。正在执行的科技部国家基础性工作专项“青藏高原多年冻土本底调查”将产出数量大、种类多的冻土本底数据。本系统为该项目设计了一个数据管理和应用的Web系统,同时也考虑了已有数据积累的归档管理。目前包括钻孔、物探、土壤、植被、监测、空间数据等六大类数据,物理实现为23个数据表。系统包括录入、管理、查询、显示、分析与应用5个主要功能模块,提供了列表、图表、地图等一系列数据可视化手段。介绍了系统和功能设计、数据库设计以及关键技术,最后列举了基本的数据应用示例。目前,温泉调查区的数据已经录入该系统,随着项目的开展,将有更多数据进入本系统,数据分析应用也将更为深入。研究结果为今后类似冻土数据库设计和实现提供参考价值。     

InSAR Permanent Scatterer analysis reveals fault re-activation during inflation and deflation episodes at Campi Flegrei caldera

Permanent Scatterers Synthetic Aperture Radar Interferometry (PSInSAR) and Global Position System (GPS) are applied to investigate the most recent surface deformation of the Campi Flegrei caldera. The PSInSAR analysis, based on SAR data acquired by ERS-1/2 sensors during the 1992-2001 time interval and by the Radarsat sensor during 2003-2007, identifies displacement patterns over wide areas with high spatial resolution. GPS data acquired by the Neapolitan Volcanic Continuous GPS network provide detailed ground velocity information of specific sites. The satellite-derived data allow us to characterize the deformation pattern that affected the Campi Flegrei caldera during two recent subsidence (1992-1999) and uplift (2005-2006) phases. PSInSAR results show the re-activation of the caldera ring-faults, intra-caldera faults, and eruptive fissures. We discuss the results in the light of the available volcanological, structural and geophysical data and propose a relationship between the structures activated during the recent unrest episodes and those responsible for the recent (< 3.8-4 ka) volcanism. The combined interpretation of the collected data show that (a) the caldera consists of two sectors separated by a N-S striking faulting zone and (b) the intra-caldera NW-SE faults and eruptive fissures in the central-eastern sector re-activated during the studied unrest episodes and represent possible pathways for the ascent of magma and/or gas to the surface. In this sector, maximum horizontal strain, recent volcanism (3.8-4 ka), active degassing and seismicity concentrate. The fault re-activation is related to the dynamics of the caldera and not to tectonic stress. The deformation fields of the uplift and subsidence episodes are consistent with hydrothermal processes and degassing from a magmatic reservoir that is significantly smaller than the large (∼ 40 km³) magma chamber responsible for the caldera formation. We provide evidence that the monitoring of the horizontal and vertical components of deformation improves the identification of active, aseismic faults. Accordingly, we suggest that future ground deformation models should include the re-activation of the detected structures.     

High-precision deformation monitoring algorithm for GBSAR system: rail determination phase error compensation

In recent years, the repeat-pass GBSAR (ground based synthetic aperture radar) system has demonstrated its capacity to acquire deformation. Nevertheless, in a variety of applications, it needs to measure the deformation with the precision up to 0.1 mm, which could not be reached by utilizing the traditional PS (permanent scatterer) algorithm in most cases. Generally, one of the main reasons could be summarized into the phase error caused by the rail determination error, because the precision of rail determination might degrade during long working hours. However, the traditional PS algorithm could not compensate for the phase error caused by the rail determination error. In order to solve the problems, we modify the conventional PS algorithm. Firstly, we deduced the transformation relationship between the rail determination error and its corresponding interferometric phase error. Then, the phase errors caused by the atmosphere and the rail determination error were jointly compensated. The experimental data, which were obtained in Fangshan District in Beijing (China), were used to test and verify the performance of the new algorithm. After the comparison between the results processed by the new algorithm and those processed by the traditional algorithm, the proposed method demonstrated its ability to obtain high-precision deformation.     

基于SARscape的干涉叠加在地表形变监测中的应用

地表形变主要表现为地震形变、地面沉降、山体滑坡等,由InSAR技术发展而来的干涉叠加通过挖掘时间序列SAR图像获取mm级的形变信息。本文介绍了干涉叠加技术的基本原理和技术流程、基于永久散射体的方法,利用2008年～2010年的23幅Cosmo-skymed数据对北京奥林匹克公园内的主要区域进行了地表形变的监测。     

Subsidence analysis of ELH Bridge through ground-based interferometric radar during the crossing of a subway shield tunnel underneath the bridge

Ground-based interferometric radar is a popular technique for the deformation monitoring and analysis of civil engineering constructions. Many researchers have applied this technique to different operative scenarios, but only a few studies have analysed deformation time series derived through ground-based interferometric radar in consideration of the effect of coloured noise. In this study, deformation information was retrieved through the joint application of ground-based interferometric radar and maximum likelihood estimation (MLE) in consideration of the effects of white and coloured noises. A case study was conducted on the subsidence of East Lake High-tech Bridge during subway shield tunnel crossing underneath this bridge (from 16 to 18 November 2016). The subsidence time series was derived through ground-based interferometric radar. Afterward, the subsidence time series was verified by levelling at an accuracy better than 0.33 mm. Furthermore, white and coloured noises were detected in the denoized subsidence time series through a spectral analysis and MLE. For the subsidence time series of Nos. 7 and 8 piers, the coloured noise amplitudes were 0.3824 and 0.6261 mm, respectively, and the white noise values were 0.0414 and 0.0610 mm, respectively. Accurate subsidence rates and accumulative subsidence were derived through MLE by using the estimated noise characteristics in the subsidence time series. The subsidence rates of Nos. 7 and 8 piers were ?0.0122 ± 0.0060 and ?0.0065 ± 0.0058 mm hour^?1, respectively, and the accumulative subsidence values were ?0.6365 and ?0.3370 mm, respectively. This finding suggests that the bridge is stable and safe.     

A comparison of TerraSAR-X, RADARSAT-2 and ALOS-PALSAR interferometry for monitoring permafrost environments, case study from Herschel Island, Canada

Interferometric synthetic aperture radar (InSAR) data sets from TerraSAR-X, RADARSAT-2 and ALOS-PALSAR are compared for their ability to detect ground movement over the continuous permafrost site of Herschel Island, Yukon Territory, Canada. All three sensors maintain good coherence within a summer season and can be used to create summer displacement products. Stacking is advantageous for the TerraSAR-X and RADARSAT-2 data sets, although mottling, possibly an interaction of the SAR with vegetation, or residual tropospheric noise, is visible, reducing the reliability of the results. RADARSAT-2 and ALOS-PALSAR provide the most promising results with the ability to form one year interval interferograms. PALSAR can also form two and three year interval interferograms. Long interval data sets spanning 2007 to 2010 identify a band of movement of 20 to 30 cm/year along the north-east coast, and a region of movement of up to 5 cm/year near the northern tip of the island. The ability to form long interval displacement products holds the most promise for permafrost monitoring, since long-term trends are of greater interest for permafrost stability than short-term seasonal changes. TerraSAR-X data have the disadvantage that year to year interferograms cannot be formed. InSAR is not the ideal monitoring technique for the large thaw slumps of Herschel Island. Although general areas of instability can be identified, specific slump detection is limited by radar look direction, and the large and abrupt slump movement, often accompanied by disintegration and collapse of slump sections, causes loss of coherence in the InSAR data. Thaw slumps may require a different interferometric approach, such as slump extent mapping from coherence loss, or the installation of corner reflectors and point target techniques. The frequent revisit and high spatial resolution of TerraSAR-X provide the best chance of maintaining coherence over thaw slumps. In general, InSAR is more successful at identifying broad areas of subtle subsidence in gentle relief, areas of terrain instability, possibly due to permafrost thaw or ground ice melt and the removal of water volume, and prior to significant slumping.     

Monitoring of large-scale deformation in mining areas using sub-band InSAR and the probability integral fusion method

The large-scale and rapid land subsidence that occurs in mining areas often leads to problems, such as densely spaced interference fringes and the temporal decorrelation of interferometric synthetic aperture radar (InSAR) interferograms. To solve these problems, sub-band InSAR is applied to monitor the large-scale deformation that occurs in mining areas. First of all, four different bandwidth images with three sub-band bandwidth parameters are used to extract simulated mining-induced subsidence with seven different deformation magnitudes. The results of the simulation experiment suggest the following conclusions. In monitoring subsidence with different deformation magnitudes using images with different bandwidths, an optimal monitoring value exists; wider image bandwidths lead to smaller optimal monitoring values and higher monitoring accuracies. Therefore, an appropriate sub-band bandwidth should be selected that depends upon the image bandwidth and the subsidence level to achieve optimal monitoring. The optimal sub-band bandwidth for monitoring subsidence of different magnitudes in mining areas is determined through simulation experiments, and these conclusions can provide a technical basis for selecting the appropriate sub-band bandwidth for the monitoring of subsidence in mining areas. Although sub-band InSAR can reduce the number of interference fringes and the difficulty of unwrapping, the simultaneous introduction of large amounts of noise leads to reduced monitoring precision, and the application of the probability integral method in the prediction of mine subsidence is more mature. Therefore, the combined use of sub-band InSAR and the probability integral fusion method to monitor mining-induced deformation is proposed in this paper. The probability integral method is used to perform noise peeling on the interferometric phases of the sub-bands to improve the monitoring accuracy of sub-band interferometry. Then, according to the results of the simulation experiment, the fusion method with the appropriate sub-band bandwidth parameters is applied to monitor the surface deformation associated with working face 52,304 from 2 December 2012 to 13 December 2012. Finally, the monitoring results are compared with the results of monitoring using conventional differential interferometric synthetic aperture radar (D-InSAR) and global positioning system (GPS) field survey data. The results show that the reliability and accuracy of the fusion method are much better than those of conventional D-InSAR in monitoring the large-scale deformation that occurs at the edges of subsidence basins.     

Landslide monitoring by corner reflectors differential interferometry SAR

Although the differential interferometric synthetic aperture radar (DInSAR) technique has the potential for monitoring ground deformation with millimetric accuracy, it still suffers from temporal and geometric decorrelation. In this paper, the corner reflectors differential interferometry synthetic aperture radar (CRDInSAR) technique was used to overcome the limitations of conventional DInSAR. We studied the basic principles of CRDInSAR, discussed the calculation of the flat earth and topographic phases based on the geometry of satellite and corner reflectors, presented the phase unwrapping approach for the sparse grid of corner reflectors, then investigated the construction of, and solution to, the unwrapped phase system equation. Subsequently, we applied CRDInSAR to monitor the displacement of the Shuping landslide in Hubei Province, China. In this study, we processed five SAR images on a descending pass acquired by the Environmental Satellite (ENVISAT) Advanced Synthetic Aperture Radar (ASAR) sensor from September 2005 to March 2006, and compared the achieved results of CRDInSAR with Global Positioning System (GPS) measurements at the same time of the SAR data acquisition assumed as reference. The result indicates a good agreement between the measurements provided by the two different techniques, which shows that CRDInSAR allows monitoring of slow landslide deformation in low coherence areas and provides accurate results.     

基于多时相干涉SAR提取地表形变的关键技术探究

基于重复轨道的合成孔径雷达差分干涉测量(D-InSAR,Differential Interferometric SAR)技术自问世以来,就被立即成为研究重点并在许多领域得到应用。但是常规D-InSAR技术易受时间、空间失相干与大气延迟等影响而有时无法得到可靠的形变信息,因此难以在实践中得到常态化应用。永久散射体技术与小基线集技术的出现,有效地克服了上述问题的制约。本文融合了两种技术的优点,介绍了多时相干涉SAR技术的关键处理步骤,并基于多时相干涉SAR技术提取了太原市2005～2009年间的形变信息。     

Assessing pre- and post-deformation in the southern Arava Valley segment of the Dead Sea Transform, Israel by differential interferometry

Differential radar interferometry, using archived ERS data over the region of the Dead Sea Transform, allows to detect ground movement (subsidence or uplift) in playas within the southern Arava Valley segment of the Dead Sea Rift. These measurements are consistent with a mean displacement rate of about 0.4 cm/month, in the direction of the radar beam, during the 8-month period preceding the Nuweiba earthquake of 22 November 1995. In the 3 years following the earthquake, the measured rate was smaller by a factor of 10. These movements are not related to salt diapirs or water pumping activities in the area. The exact location, along faults, suggests a possible correlation with pre-seismic and post-seismic fault deformation.A simple fault model consistent with the observed phenomena associates the observed subsidence/uplift to right and left stepping en-echelon fault patterns related to inter-seismic tensional accumulation along the faults. Further observations are necessary on this site and similar fault areas to corroborate the correlation between seismic activity and the observed phenomena. Monitoring of these sites should continue with differential Global positioning system (GPS) measurements and radar interferometric analysis using Envisat and Radarsat as well as archived data (including J-ERS).     

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.     

Persistent Scatterers Interferometry detects and measures ground subsidence in Lisbon

Results from the application of Persistent Scatterers Interferometry in Lisbon Metropolitan Area revealed two previously unknown subsiding urban areas: one (Laranjeiras) is located in the center of Lisbon; another (Vialonga) is to be found toward the North, in an industrial region crossed by Lisbon's main highway and railway lines. The two subsiding sectors are bordered by sharp velocity gradients, and the subsidence pattern appears partially delimited by mapped geologic faults. Surface geology and urbanization alone are unable to explain the phenomena. In the Vialonga area, the historical record of water pore pressure shows a clear decline of the levels (up to 65 m in 27 years), providing evidence of over-exploitation of groundwater resources. Limited information from wells drilled inside and outside the subsidence area points to a spatial correlation between the subsidence and the water pressure levels, and suggests that faults could be acting as hydraulic barriers in the aquifer system. The surface subsidence detected is probably caused by compaction of a clay-rich Oligocene-aged aquitard, led by over-exploitation of adjacent aquifers. The same Oligocene aquitard layer is present in the Laranjeiras area, immediately bellow a multi-layered sand-clay-limestone Miocene aquifer, but further work is needed to diagnose the possibility of over-exploitation of groundwater here. In this work we were able to independently confirm the PSI results, by comparing autonomous PSI results processed for the same geographical areas, and by comparing PSI with leveling and continuous GPS derived subsidence velocities, whose close match provided further ground validation of the space-borne PSI technique.