Spaceborne differential radar interferometry has proven a remarkable potential for mapping ground deformation phenomena (e.g., urban subsidence, volcano dynamics, coseismic and postseismic ...displacements along faults, as well as slope instability). However, a full operational capability has not been achieved yet due to atmospheric disturbances and phase decorrelation phenomena. These drawbacks can often be-at least partially-overcome by carrying out measurements on a subset of image pixels corresponding to natural or artificial stable reflectors permanent scatterers (PS) and exploiting long temporal series of interferometric data. This approach allows one to push the measurement precision very close to its theoretical limit (in the order of /spl sim/1 mm for C-band European Remote Sensing (ERS)-like sensors). In this paper, the detection of both time-uniform and seasonal deformation phenomena is addressed, and a first assessment of the precision achievable by means of the PS Technique is discussed. Results highlighting deformation phenomena occurring in two test sites in California are reported (Fremont in the Southern Bay Area and San Jose in the Santa Clara Valley).
This paper presents the results of a blind experiment that is performed using two pairs of dihedral reflectors. The aim of the experiment was to demonstrate that interferometric synthetic aperture ...radar (InSAR) measurements can indeed allow a displacement time series estimation with submillimeter accuracy (both in horizontal and vertical directions), provided that the data are properly processed and the impact of in situ as well as atmospheric effects is minimized. One pair of dihedral reflectors was moved a few millimeters between SAR acquisitions, in the vertical and east-west (EW) directions, and the ground truth was compared with the InSAR data. The experiment was designed to allow a multiplatform and multigeometry analysis, i.e., each reflector was carefully pointed in order to be visible in both Envisat and Radarsat acquisitions. Moreover, two pairs of reflectors were used to allow the combination of data gathered along ascending and descending orbits. The standard deviation of the error is 0.75 mm in the vertical direction and 0.58 mm in the horizontal (EW) direction. GPS data were also collected during this experiment in order to cross-check the SAR results
Interferometric Synthetic Aperture Radar (InSAR) data, gathered over the In Salah CO2 storage project in Algeria, provide an early indication that satellite‐based geodetic methods can be effective in ...monitoring the geological storage of carbon dioxide. An injected mass of 3 million tons of carbon dioxide from one of the first large‐scale carbon sequestration efforts, produces a measurable surface displacement of approximately 5 mm/year. Using geophysical inverse techniques, we are able to infer flow within the reservoir layer and within a seismically detected fracture/fault zone intersecting the reservoir. We find that, if we use the best available elastic Earth model, the fluid flow need only occur in the vicinity of the reservoir layer. However, flow associated with the injection of the carbon dioxide does appear to extend several kilometers laterally within the reservoir, following the fracture/fault zone.
Reservoir monitoring improves our understanding of reservoir behaviour and helps achieve more effective reservoir management and prediction of future performance with obvious economic benefits. It ...relies on an integrated approach involving both surveillance (well or surface based; seismic, electrical, leakage, flow and deformation measurements, etc.) and modelling. Surface deformation monitoring can provide valuable constraints on the dynamic behaviour of a reservoir enabling the evaluation of volumetric changes in the reservoir through time. Levelling campaigns, tiltmeters, GPS permanent stations and Permanent Scatterer SAR Interferometry (PSInSAR™) are the techniques most widely used to determine surface displacements. Whatever the surveying technique, the detection of millimetre-level surface deformation is required to monitor small surface displacement rates that could impact risk evaluation and land use planning. Depending on depth and reservoir/overburden rheology, volumetric changes in reservoirs due to fluid extraction and injection can induce either subsidence or uplift that could trigger fault reactivation and threaten well integrity; deformation may also be detectable at the surface. Mapping surface effects accurately requires hundreds of observation points per km
2 which cannot be delivered by traditional monitoring methods without unacceptably large expenditure. PSInSAR™ is one of the most promising and cost-effective techniques capable of providing high precision and high areal density displacement measurements over long periods of time. Moreover, the availability of PS data for both ascending and descending orbits enables the estimation of both vertical and E–W horizontal displacement fields. Two case histories will be presented to illustrate the advantages of PSInSAR™ technology for the detection of surface deformation induced by reservoir exploitation and monitoring of its evolution though time.
Permanent Scatterer SAR Interferometry (PSInSAR) aims to identify coherent radar targets exhibiting high phase stability over the entire observation time period. These targets often correspond to ...point-wise, man-made objects widely available over a city, but less present in non-urban areas. To overcome the limits of PSInSAR, analysis of interferometric data-stacks should aim at extracting geophysical parameters not only from point-wise deterministic objects (i.e., PS), but also from distributed scatterers (DS). Rather than developing hybrid processing chains where two or more algorithms are applied to the same data-stack, and results are then combined, in this paper we introduce a new approach, SqueeSAR, to jointly process PS and DS, taking into account their different statistical behavior. As it will be shown, PS and DS can be jointly processed without the need for significant changes to the traditional PSInSAR processing chain and without the need to unwrap hundreds of interferograms, provided that the coherence matrix associated with each DS is properly "squeezed" to provide a vector of optimum (wrapped) phase values. Results on real SAR data, acquired over an Alpine area, challenging for any InSAR analysis, confirm the effectiveness of this new approach.
Ground deformation studies based on Differential GPS (DGPS) measurements and Permanent Scatterer Interferometric (PSI) analysis have been conducted on the islands of Cephalonia and Ithaca covering ...the period 1992 to 2010. DGPS measurements for the period 2001 to 2010 revealed horizontal clockwise rotation of Cephalonia and velocities ranging from 3 to 8mm/yr with the largest values occurring at the western and southern parts of the island. Considering its vertical deformation, two periods are distinguished on the basis of DGPS and PSI: The first one (1992 to 2003) shows generally an almost linear slight subsidence (around 1mm/yr) which is consistent with expected neotectonic movements of the island. The second one (2003 to 2010) has been tentatively attributed to dilatancy in which reversal to uplift (2–4mm/yr) occurred mainly along the southern and southeastern parts of the island, while larger magnitudes (>4mm/yr) took place at the western part. These non-linear high rates of uplift started at about mid-2005, and were of increasing rate at the southern part, but of decreasing rate at the western part; they may indicate a major regional crustal deformation process in an environment that has previously supported offshore large magnitude earthquakes. Parallel analysis of the observed seismicity in the broader area identified two seismically critical areas on the basis of the decelerating–accelerating seismicity: a major one south of Cephalonia and west of Zakynthos, and another minor one at the NW part of Peloponnese. Critical time estimates of the occurrence of a future strong seismic event in the above critical areas were also made based on: (i) accelerating seismicity, and (ii) the temporal analysis of the seismicity.
► Ground deformation in Cephalonia using DGPS, PSInSAR. ► Strong uplift observed after 2003 interpreted as dilatancy. ► Seismicity Pattern Analysis. ► Seismically critical area determined. ► Critical time of major seismic event estimated.
Coastal regions are increasingly affected by larger storms and rising sea level predicted by global warming models, aggravating the situation in the city of Venice where tidal‐induced seasonal ...flooding coupled with natural and anthropogenic subsidence have been perennial problems. In light of accelerated efforts to protect Venice from the rise in sea level we assess land subsidence in the Venice Lagoon over the last decade. Through a combined analysis of GPS position time series from 2001.55 to 2011.00 for four stations installed by the Magistrato alle Acque di Venezia and thousands of observations of InSAR permanent scatterers using RADARSAT‐1 images from 2003.3 to 2007.85, we determine that the northern lagoon subsides at a rate of 2–3 mm/yr, whereas the southern lagoon subsides at 3–4 mm/yr. The city of Venice continues to subside, at a rate of 1–2 mm/yr, in contrast to geodetic studies in the last decade of the 20th Century suggesting that subsidence has been stabilized. The GPS results indicate a general eastward tilt in subsidence and that the natural subsidence rate related to the retreat of the Adriatic plate subducting beneath the Apennines is at least 0.4–0.6 mm/yr. Our combined GPS and InSAR analysis demonstrates high spatial resolution in the vertical direction with a precision of 0.1–0.2 mm/yr with respect to a global reference frame. Continued efforts to secure the city of Venice from flooding must also take into account the significant local and regional subsidence rates as well as the expected rise in sea level.
Key Points
Natural land subsidence in Venice must be considered in effort to save the city
Natural subsidence in Venice is of the same order of magnitude as sea level rise
Accuracy of subsidence from GPS/InSAR integration is 0.1‐0.2 mm/yr global frame
The Santorini Volcanic Complex (SVC) has been in a dormant state for the last 60years until January 2011 when upward influx of magma reawakened the volcano with intense radial ground deformation and ...inter-caldera seismicity that lasted until January 2012 but declined afterwards. This paper aims to study the ground deformation and the inferred tectonic implications of the SVC for the period 1992–2012 mainly based on the SqueeSAR™ technique and DGPS campaign results of our local network which incorporates available data on Internet from several continuous GPS stations established on the island. The spatial deformation of the SVC during the quiet period 1992–2010 was deduced by joint analysis of ERS1 and 2 and ENVISAT. It was found that the intra caldera Palaea Kammeni shield volcano was being uplifted (2–3mm/yr) with increasing rate, whilst the adjacent Nea Kammeni shield volcano was being subsided (up to 6mm/yr) with increasing rate. The rest of the SVC showed a velocity field varying from −1 to +2mm/yr, indicating a rather linear deformation during that period. The results from the GPS network are in full agreement with the SqueeSAR results. Based on the results of SqueeSAR analysis of 12 ENVISAT images, and DGPS/CGPS data to end 2012, the deformation for the unrest period 2011–2012 was non-linear being characterized by strong radial deformation in the northern part of the caldera (50–120mm/yr), and accelerating values (>130mm/yr2). Combined GPS/SqueeSAR Mogi modeling indicated a source located north of Nea Kammeni at a shallow depth. However, a progressively decreasing rate in deformation was noted at most GPS/CGPS station components after January 2012, indicating magma settlement consistent with the constantly decreasing rate of the inter-caldera seismicity. The faulting features seem to have a key role in the evolution of the deformation, which continues up the end 2012, but at a very low level.
•Ground deformation in Santorini Volcanic Complex (Greece) 1992–2012•Small amplitude linear deformation for the period 1992–2010•2011–2012: unrest period of Santorini Volcano•Inter-caldera seismicity and strong deformation (>100mm)•Deformation was simulated with a MOGI source model.
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