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Hernandez-Espriu A.,National Autonomous University of Mexico | Reyna-Gutierrez J.A.,National Autonomous University of Mexico | Reyna-Gutierrez J.A.,Technical University of Denmark | Sanchez-Leon E.,National Autonomous University of Mexico | And 7 more authors.
Hydrogeology Journal | Year: 2014

Mexico City relies on groundwater for most of its domestic supply. Over the years, intensive pumping has led to significant drawdowns and, subsequently, to severe land subsidence. Tensile cracks have also developed or reactivated as a result. All such processes cause damage to urban infrastructure, increasing the risk of spills and favoring contaminant propagation into the aquifer. The effects of ground deformation are frequently ignored in groundwater vulnerability studies, but can be relevant in subsiding cities. This report presents an extension to the DRASTIC methodology, named DRASTIC-Sg, which focuses on evaluating groundwater vulnerability in urban aquifers affected by differential subsidence. A subsidence parameter is developed to represent the ground deformation gradient (Sg), and then used to depict areas where damage risk to urban infrastructure is higher due to fracture propagation. Space-geodetic SqueeSAR data and global positioning system (GPS) validation were used to evaluate subsidence rates and gradients, integrating hydrogeological and geomechanical variables into a GIS environment. Results show that classic DRASTIC approaches may underestimate groundwater vulnerability in settings such as the one at hand. Hence, it is concluded that the Sg parameter is a welcome contribution to develop reliable vulnerability assessments in subsiding basins. © 2014 Springer-Verlag Berlin Heidelberg.

D'Aria D.,ARESYS | Ferretti A.,Tele Rilevamento Europa TRE | Ferretti A.,TRE Canada Inc. | Guarnieri A.M.,ARESYS | And 2 more authors.
IEEE Transactions on Geoscience and Remote Sensing | Year: 2010

We propose a calibration method suitable for a set of repeated synthetic aperture radar (SAR) acquisitions that uses both absolute calibrated devices (such as corner reflectors) and stable targets identified in the scene [the permanent scatterers (PSs)]. Precisely, the role of the PS is to extend the initial calibration sequence by monitoring the radiometric stability of the system throughout the whole mission life span. At a first step, this paper approaches the problem of PS-based normalization by an iterative maximum-likelihood method that exploits the stack of complex interferometric SAR images. Two solutions are given based on different assumptions on the PS phases. As a second step, the merging of these estimates with the available calibration information is discussed. Results achieved by experimental acquisitions are shown in two different SAR systems: 1) a C-band spaceborne SAR and 2) a Ku-band ground-based SAR. © 2009 IEEE.

Ferretti A.,Tele Rilevamento Europa T.R.E. Srl | Tamburini A.,Tele Rilevamento Europa T.R.E. Srl | Novali F.,Tele Rilevamento Europa T.R.E. Srl | Fumagalli A.,Tele Rilevamento Europa T.R.E. Srl | And 2 more authors.
Energy Procedia | Year: 2011

Surface deformation monitoring provides unique data for observing and measuring the performance of producing hydrocarbon reservoirs, for Enhanced Oil Recovery (EOR) and for Carbon Capture and Storage (CCS). To this end, radar interferometry (InSAR), particularly multi-interferogram Persistent Scatterer (PS) techniques, such as PSInSAR™, are innovative, valuable and cost-effective tools. Depending on reservoir characteristics and depth, oil or gas production can induce surface subsidence or, in the cases of EOR and CCS, ground heave, potentially triggering fault reactivation and in some cases threatening well integrity. Mapping the surface effects of fault reactivation, due to either fluid extraction or injection, usually requires the availability of hundreds of measurement points per square km with millimeter-level precision, which is time consuming and expensive to obtain using traditional monitoring techniques, but can be readily obtained with InSAR data. Moreover, advanced InSAR techniques developed in the last decade are capable of providing millimeter precision, comparable to optical leveling, and a high spatial density of displacement measurements over long periods of time, without the need for installing equipment or otherwise accessing the study area. Until recently, a limitation to the application of InSAR was the relatively long revisiting time (24 or 35 days) of the previous generation of C-band satellites (ERS1-2, Envisat, Radarsat). However, a new generation of X-band radar satellites (TerraSAR-X and the COSMO-SkyMed constellation), which have been operational since 2008, are providing significant improvements. TerraSAR-X has a repeat cycle of 11 days, while the joint use of two sensors of the COSMO-SkyMed constellation have an effective repeat cycle of just 8 days. With the launch of the fourth satellite of the constellation, in 2010, COSMOSkyMed will have an effective revisiting time of just 4 days, allowing "near real-time" applications. Indeed, by combining two acquisition geometries (e.g. data acquired along ascending and descending orbits), it will be possible, on average, to have a new scene over the area of interest every other day. Additional advantages of the new X-band satellites are: a higher sensitivity to target displacement and a higher spatial resolution (the density of measurement points can be increased by an order of magnitude, possibly exceeding 2,500 PS/km 2). In this paper, we present some examples of the application of X-band SAR data to reservoir monitoring. Special attention will be given to CCS projects where InSAR data could become a "standard" monitoring tool. The paper will highlight the technical features of the new sensors, the possible synergy between TerraSAR-X and COSMOSkyMed data, as well as the importance of a careful analysis of atmospheric disturbances affecting SAR data covering the area of interest, in order to retrieve high quality displacement data. Finally, some conclusions will be drawn supporting recommendations about future CCS monitoring programs. © 2011 Published by Elsevier Ltd.

Eneva M.,Imageair, Inc. | Adams D.,Imageair, Inc. | Falorni G.,TRE Canada Inc. | Novali F.,TRE. s.r.l. | Hsiao V.,TRE Canada Inc.
Transactions - Geothermal Resources Council | Year: 2014

Interferometric synthetic aperture radar (InSAR) is applied to data from the TerraSAR-X (TSX) satellite, collected in the period August 2012 - October 2013 in the area of the Salton Sea geothermal field in southern California, for the purpose of detecting surface deformation. These data are from a new generation of satellites, with much improved spatial resolution and frequency of temporal coverage than earlier satellites like Envisat (2003-2010). The particular technique applied, SqueeSAR™, uses permanent and distributed scatterers, which makes it possible to observe deformation in agricultural areas, where conventional InSAR does not work. Surface deformation is first obtained in the line-of-sight (LOS) to the satellite from two orbital geometries, descending and ascending. The two LOS measurements are then used to calculate horizontal and vertical displacements. The TSX deformation time series and annual rates are compared with those previously derived from Envisat. The periods covered by the two satellites present an unprecedented opportunity to observe ongoing post-production surface deformation at the CalEnergy units of the geothermal field, operated since early 1980's, and both pre- and post-production deformation at the new Hudson Ranch-1 (HR-1) development of EnergySource, which started in early 2012. Two subsidence bowls at the CalEnergy units have been confirmed by the TSX results, similar to earlier Envisat observations, with annual subsidence rates of up to -30 mm/year relative to a benchmark on Obsidian Butte (S-1246). However, there is a clear difference between the pre- and post-production periods at the new HR-1 development, with a relative uplift (compared to S-1246) turning into a subsidence of up to -18 mm/year. Nonetheless, the possibility for anthropogenic origin of the surface deformation at this field is challenged by non-anthropogenic factors associated with the regional and local tectonics, as well as the receding Salton Sea. Copyright © (2014) by the Geothermal Resources Council.

Eneva M.,Imageair, Inc. | Falorni G.,TRE Canada Inc. | Teplow W.,U.S. Geothermal Inc. | Morgan J.,TRE Canada Inc. | And 2 more authors.
Transactions - Geothermal Resources Council | Year: 2011

As part of a DOE project, we have applied satellite radar interferometry (InSAR) to detect surface deformation in the San Emidio geothermal field, Nevada. The specific method used, SqueeSAR™, is the latest innovation in the field of InSAR, which allows obtaining deformation time series at locations of permanent and distributed scatterers (PS and DS, respectively). The PS points are relatively small objects such as buildings, wellheads, boulders, etc., which remain coherent from one satellite scene to another. The DS are coherent areas covering several pixels emitting weaker signals than the PS, but still have acceptable signal-to-noise ratios. The PS and DS play the role of numerous benchmarks, at which surface deformation rates can be determined. Three sets of radar data were used covering an area of 60 km 2. The datasets included imagery from the European ERS-1, ERS-2, and Envisat satellites. They consisted of 38 ERS-1/2 scenes acquired from descending orbits (satellite moving north to south) during the period May 1992 - January 2001, 53 descending Envisat images collected between June 2004 and April 2010, and 45 ascending (satellite moving south to north) Envisat scenes from the period October 2003 - June 2010. Due to the desert environment of the study area, numerous PS and DS were identified - more than 180,000 from the ERS descending, 212,000 from the Envisat descending, and 166,000 from the Envisat ascending scenes. Surface deformation at the individual PS and DS locations is first determined in the line-of-sight (LOS) direction to the satellite; i.e., in terms of movement towards or away from it. The availability of Envisat data from two orbit geometries (descending and ascending) makes it possible to decompose the LOS deformation into vertical displacements and movements in the west-east horizontal direction. Due to the steep look angle of the satellites (∼21° to 22°), the vertical and the LOS movements are very similar. However, the west-east horizontal component of deformation is only revealed by the decomposition procedure. The LOS time series were used to derive surface deformation rates at all individual PS and DS locations, while vertical and west-east horizontal rates were extracted from the combinations of descending and ascending LOS rates. Distinct areas of subsidence and uplift are outlined, with changing spatial patterns in time, especially from the older ERS data set to the newer Envisat data. We observe surface deformation (Figure Presented) in the area of the production wells, and profiles transecting faults indicate distinct signals, likely resulting from hydrological control. Many of the deformation time series exhibit obvious seasonal patterns, with varying amplitudes throughout the study area. We continue to examine these uniquely rich results for clues to describe the geothermal resource at San Emidio.

Falorni G.,TRE Canada Inc. | Morgan J.,TRE Canada Inc. | Eneva M.,Imageair, Inc.
Transactions - Geothermal Resources Council | Year: 2011

InSAR is a remote sensing tool that has applications in both geothermal exploration and in the management of producing fields. The technique has developed rapidly in recent years and the most evolved algorithms, now capable of providing precise ground movement measurements with unprecedented spatial density over large areas, allow, among other things, the monitoring of the effects of fluid injection and extraction on surface deformation and the detection of active faults. Multi-interferogram approaches have been used at several geothermal sites in the US and abroad. Two examples are presented here with the aim of illustrating how these techniques are being used for different stages of geothermal exploration and management. In both cases, multiple advanced InSAR techniques were used to quantify surface expression patterns, with a focus on the SqueeSAR™ approach, the latest breakthrough in InSAR technology. The first case study examines the Salton Sea area (California), where multi-interferogram InSAR provided an overview of surface deformation at a producing geothermal reservoir. Surface deformation in this area was complex, and the added detail provided insight into the interplay of tectonics and production activities. The second example involves the use of InSAR within a suite of tools for exploration of the San Emidio geothermal field in Nevada, as part of a DOE funded initiative. This project aimed to develop geophysical techniques to identify and map large aperture fractures for the placement of new production/exploration wells. Additional InSAR studies have also been carried out at several areas in Nevada, including the Brady and Desert Peak fields and in California at the Geysers field. These studies, along with ongoing developments in radar satellite technology and in the field of InSAR, show considerable promise for the future monitoring of geothermal production facilities.

Eneva M.,Imageair, Inc. | Adams D.,Imageair, Inc. | Falorni G.,TRE Canada Inc. | Morgan J.,TRE Canada Inc.
Transactions - Geothermal Resources Council | Year: 2012

In a current California Energy Commission (CEC) project, satellite radar interferometry (InSAR) is applied to detect surface deformation in several areas of the Imperial Valley in southern California. These areas include established, new and possible future geothermal fields, as well as nearby fault zones. The InSAR technique used, SqueeSAR™, is the latest innovation in the field of radar interferometry. It makes it possible to obtain deformation time series at locations of permanent and distributed scatterers (PS and DS), playing the role of numerous benchmarks. The deformation time series are then used to estimate annual deformation rates. The PS represent points aligned along roads and canals, buildings, wellheads, etc., which remain coherent from one satellite image to another. The DS cover several pixels in the satellite scenes and emit weaker signals than the PS, but still above the backscatter noise. The SqueeSAR™ technique works well for vegetated and rural areas and thus provides unique results from the agricultural lands of Imperial Valley. The radar scenes used for the analysis are from the Envisat satellite, over the period 2003-2010. Two data sets were used, consisting of 45 descending and 33 ascending images, for which the satellite moved from north to south and south to north, respectively. In this paper the focus is on three geothermal fields - Salton Sea (SSGF), Heber (HGF), and East Mesa (EMGF). Preliminary results show that distinct areas of subsidence are seen in all of these fields. Earlier results from a two-year study using data from another satellite for the SSGF, are confirmed in the present work. At the HGF, there is also evidence of uplift. Radar interferometry provides unprecedented information on surface deformation, with great spatial and temporal detail, which cannot be achieved by any ground-based means. In this capacity, it has applications for pre-production reservoir assessment, ongoing exploration, and mitigation of any environmental impact that might occur.

Eneva M.,Imageair, Inc. | Adams D.,Imageair, Inc. | Falorni G.,TRE Canada Inc. | Morgan J.,TRE Canada Inc.
Transactions - Geothermal Resources Council | Year: 2013

Interferometric synthetic aperture radar (InSAR) is applied to data from the Envisat satellite, collected in the period 2003-2010, to detect surface deformation at the Heber geothermal field in Imperial Valley of southern California. The particular technique applied, SqueeSAR™ developed at TRE, makes use of permanent and distributed scatterers. This makes it possible to observe deformation in agricultural areas, where conventional InSAR does not work, so our results are the first of this kind for Heber. Observations are obtained first in the line-of-sight (LOS) to the satellite from two orbital geometries, descending and ascending, and are subsequently used to calculate horizontal movements in the west-east direction, as well as vertical displacements. Maps of annual deformation rates derived from the satellite data (2003-2010) show two adjacent areas of subsidence and uplift at Heber, confirming observations from annual ground-based leveling surveys. As to the horizontal movements in these areas, they are westward in the uplift area and eastward in the subsidence area. Maximum LOS rates away from the satellite (indicative of subsidence) reach -46 mm/year, while maximum LOS rates toward the satellite (indicative of uplift) reach +22 mm/year. However, the uplift is only taking place after 2005, prior to which the leveling data show mostly subsidence traced back to the beginning of leveling data availability from 1994. These changing trends of surface deformation in the 2003-1010 uplift area can be readily traced to changes in injection volumes. Examples of rates along profiles and mean deformation time series within small polygons of interest are also shown. The results demonstrate the utility of InSAR for geothermal operations management, planning, and environmental impact mitigation.

Solano-Rojas D.,University of Miami | Cabral-Cano E.,National Autonomous University of Mexico | Hernandez-Espriu A.,National Autonomous University of Mexico | Wdowinski S.,University of Miami | And 4 more authors.
Boletin de la Sociedad Geologica Mexicana | Year: 2015

The process of land subsidence in the Mexico City Metropolitan Area has been recognized since the beginning of the last century and poses severe challenges for the operation and maintenance of the city's infrastructure. In this work we present land subsidence velocity results from Persistent Scatterers (PSs) through a SqueeSAR interferometric analysis of ENVISAT-ASAR Synthetic Aperture Radar data acquired during the 2003-2010 period from nine continuous GPS stations. We then investigated the relationship between the observed subsidence rates and the groundwater level decrease obtained from 180 water well hydrographs distributed throughout the Mexico City Metropolitan Area. Geodetic results indicate differences in land subsidence in the vicinity of the GPS stations, ranging from stable (zero subsidence zones), to slow and rapid subsidence zones. The highest subsidence rates occur in sites with very low local subsidence gradients within the lacustrine sector of the city and vertical GPS velocities of up to -273 mm/yr. Areas with very high local subsidence gradients induce the greatest hazard as they increase the potential for shallow tensile cracks and faulting. The analysis of well hydrographs over the last 20 years indicates groundwater drawdowns of up to 30 m in the most severe cases; groundwater level recovery occurs in very few cases, and only where well locations are within areas of very low subsidence rates. Declining groundwater levels are found throughout the entire range of subsidence values, suggesting that the aquifer-aquitard system is under severe stress due to the extreme groundwater extraction that far exceeds the magnitude of natural recharge. The low correlation between the subsidence rates and the decrease in groundwater levels further suggests that additional variables play an important role in the subsidence process, such as the lithology, the aquitard thickness, water content, the elasto-plastic behavior of the hydrostratigraphy, the drop in pore pressure and groundwater overdraft. A positive correlation is found between land subsidence rates and the thickness of the upper aquitard.

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