On the 8th of February 2016, a Mw 4.2 earthquake was detected inside the Los Humeros caldera, located in the eastern sector of the Trans-Mexican Volcanic Belt. The event occurred after a sharp increase in the injection rate at the Los Humeros Geothermal Field and it was recorded by the seismic monitoring network of the power plant. The earthquake was felt by the local population and it caused damage in the power plant infrastructure. The focal mechanism solution of a previous study based on seismological data shows a reverse movement with a minor left-lateral component: Mw=4.2, depth=1500m, strike=169°, dip=61°, rake=42°. We have performed a geodetic and geomechanical analysis of the seismic source event based on ground deformation inferred from DInSAR. We used ascending and descending Sentinel-1 differential interferograms to retrieve the horizontal and vertical components of the co-seismic deformation. Subsequently, we inverted the estimated deformation to obtain the solution of an activated fault using the Okada model. These results shed light on the geomechanical aspects of the event and can help to understand the effects of field operations interacting with pre-existing structural features and active tectonic processes in the Los Humeros caldera.@en

Within the Netherlands, 24 geothermal systems have been realized of which 16 are operational, together producing 3.4 PJ of heat in 2018 (status date 1-1-2019). The main application domain is horticulture. The ambition of the Dutch government is to see production of geothermal energy increase in the Netherlands to 50 PJ in 2030, subsequently 200 PJ in 2050 and also to expand the application domain to district heating and industry. A state of the art resource assessment can support the Dutch government policy to realize its ambition. By classifying the resources based on project maturity including reference to the obstructing issues in the maturation of projects such as technical, financing, licensing and or social and environmental complexities targeted policy can be drafted. As of January 2019, 51 exploration licenses have been granted, and 31 more have been applied for (MEA2019). At least one geothermal project is defined in each of these exploration licenses, at different levels of advancement. Outside the boundaries of existing licenses and licenses under application, the Netherlands provides ample space for geothermal development. At the moment, there are no tools or practical methodologies to integrate all available information in a coherent and automated manner. As such, a method to quantify the geothermal energy resources of projects ‘not yet realized’ using the United Nations Framework Classification (UNFC) resource classification system would help policymakers to decide upon the most appropriate measures to remove obstructions for reaching the 2030-2050 geothermal ambitions. In this study, we show the initial results of a resource assessment and classification system for geothermal energy while incorporating environmental and social issues in the classification, as required by the UNFC2009. As basis for this resource assessment, we use the web tool ThermoGIS-v2.1 (Vrijlandt et al. 2019). ThermoGIS-v2.1 using information on the Dutch subsurface derived from the regional mapping by the Geological Survey. It is updated through incorporation of newly gained insights and data and provides a comprehensive overview of the geothermal potential for a selected set of aquifers. The resource estimates, including the uncertainty range related to these figures, at the status date 1-1-2019 of the Dutch geothermal “project portfolio” are classified using UNFC, resulting in a set of resource figures per resource class according to project maturity: commercial, potentially commercial, non-commercial and exploration projects. @en

Surface deformation due to fluid extraction can be detected by satellite-based geodetic sensors, providing important insights on subsurface geomechanical properties. In this study, we use Differential Interferometric Synthetic Aperture Radar (DInSAR) observations to measure ground deformation due to fluid extraction at the Los Humeros Geothermal Field (Puebla, Mexico). Our main goal is to reveal the pressure distribution in the reservoir and to identify reservoir compartmentalization, which can be important aspects for optimizing the production of the field. The result of the PS-InSAR (Persistent Scatterer by Synthetic Aperture Radar Interferometry) analysis shows that the subsidence at the LHGF was up to 8 mm/year between April 2003 and March 2007, which is small relative to the produced volume of 5×106 m3/year. The subsidence pattern indicates that the geothermal field is controlled by sealing faults separating the reservoir into several blocks. To assess if this is the case, we relate surface movements with volume changes in the reservoir through analytical solutions for different types of nuclei of strain. We constrain our models with the movements of the PS points as target observations. Our models imply small volume changes in the reservoir, and the different nuclei of strain solutions differ only slightly. These findings suggest that the pressure within the reservoir is well supported and that reservoir recharge is taking place.@en

Torfajökull volcano, Iceland, has not erupted since 1477. However, intense geothermal activity, deformation, and seismicity suggest a long‐lasting magmatic system. In this paper, we use ambient noise tomography to image the magmatic system beneath Torfajökull volcano. One hundred days of ambient noise data from 23 broadband seismometers show the consistent presence of double‐frequency microseism noise with significant power between ∼0.1 and 0.5 Hz. Beamforming results indicate microseism noise with persistent higher energy propagating from west and SE directions and apparent velocities below 3 km/s. We use ambient noise seismic interferometry to retrieve Rayleigh waves, and we introduce a method to estimate the reliability of the retrieved surface waves. We find stable estimation of surface wave phase velocities between 0.16 and 0.38 Hz. Azimuthal velocity variations show a trend of higher velocities in the NE/SW direction, the strike of the rift zone intersecting Torfajökull, and orientation of erupted lavas on a NE‐SW fissure swarm. Tomographic results indicate low‐velocity anomalies beneath the volcano caldera (between −5% and −10%) and even lower velocity variations in the southeast and southwest study area (below −10%), outside the volcano caldera. Low anomalies may indicate the existence of hot material, more prominent outside the caldera outskirts. High‐velocity variations (between 5% and 10%) outline the volcano caldera between 4‐ and 5‐km depth and more pronounced velocities (between 10% and 15%) up to 5‐km depth in the north of the volcano caldera. We interpret the former as possible caldera collapse structure and the latest as solidified intrusive magma from the old preferred magma paths.@en

Integration of results from active seismic, passive seismic and well data reduces the uncertainties of several subsurface parameters that are of interest for cost-effective geothermal production operations in Los Humeros. In this study, we present results from the application of ambient noise seismic interferometry (ANSI) to retrieve zero-offset reflected P-waves from continuous seismic data recorded at the Los Humeros geothermal field, Mexico. This study is inspired by encouraging results from the application of ANSI for body wave reflection retrieval that was reported in 2016 for a geothermal field located at Reykjanes peninsula, Iceland (Verdel et al., 2016). Continuous broadband and short-period seismic recordings provided insightful reflection information that corresponded well, in relevant depth intervals, with reflectivity retrieved from the correlation of coda waves from a distant but very strong earthquake. That work was carried out within the context of EU’s Seventh Framework research and innovation program IMAGE. Encouraged by these findings, it was decided to conduct a new study following a similar approach within the context of the GEMex project, a European-Mexican collaboration. The purpose of GEMex is to gain an improved understanding of the geological structure and geothermal reservoir behaviour for two geothermal fields: Los Humeros and Acoculco. In the following, we address data selection and processing aspects related to the retrieval of reflected P-waves from Los Humeros seismic noise recordings. The retrieved reflections are compared with modelled reflectivities at two station locations at a close distance from the location where the seismic interval velocities that are used in the modelling were available from the literature. The reflected P-wave information provides structural detail about the field at locations directly underneath the employed seismic stations.@en

Tomographic imaging based on ambient seismic noise measurements has shown to be a powerful tool, especially in areas like Iceland, where the microseism illumination is excellent. In this paper, we produce a 3D S-wave tomographic image over the western Reykjanes Peninsula high-enthalpy geothermal fields and evaluate the reliability of the tomographic results for different resolutions through simulated and real data. We use 30 broadband stations operating for approximately one-and-a-half year and apply ambient noise seismic interferometry for each station-pair. This results in empirical Green's functions in which especially the ballistic surface waves (BSW) are well resolved. The retrieved BSW exhibit a high signal-to-noise ratio between 0.1 and 0.5 Hz, and the beamforming analysis indicates an apparent surface-wave velocity of 3 km/s over a broad azimuthal range. For the tomographic inversion, we invert the estimated phase velocities between all station pairs to frequency-dependent phase velocity maps in four different resolutions (1, 2, 3, and 4 km) using a Tikhonov regularisation. With the estimated regularisation parameter per frequency per resolution, we invert simulated data for checkerboard sensitivity tests per frequency for different combinations of velocity anomaly sizes and resolutions.

Finally, after the inversion to depth, we detect S-wave velocity anomalies with variations between −15% and 15% with reference to an estimated average velocity using 1 km and 3 km of lateral resolutions and 1 km of vertical resolution. This study shows the potential of ambient noise tomography as complementary seismological tool for reservoir characterization.@en

Tomographic studies based on passive seismic measurements have proven to be a powerful tool to image the subsurface. This especially holds in areas like Iceland, where the microseism coverage arriving from the ocean is excellent. In this study, we apply Ambient Noise Seismic Interferometry (ANSI) to generate a tomographic image of Rayleigh-waves velocity anomalies to further invert for S-wave anomalies at two Icelandic locations. We derive a tomographic image over Reykjanes Peninsula geothermal system using 30 Broad-Band (BB) stations deployed under the IMAGE (Integrated Methods for Advanced Geothermal Exploration) project framework and operated for approximately one year and a half. In the other case study, we derive a tomographic image of Torfajökull volcano using 23 BB seismometers that recorded ambient noise for 100 days. The later data were acquired in 2005 by Cambridge University. We retrieve the surface-wave part of the Green’s functions by cross-correlation between station pairs and consecutive stacking of the cross-correlations to obtain coherent ballistic surface waves (BSW). We pick the arrival times of the BSW, which are the input for the tomographic analysis. Both datasets show remarkably high signal-to-noise ratio of surface-wave arrivals between 0.1 and 0.5 Hz, even with only 100 days of recorded ambient noise. A beamforming analysis indicates a broad azimuthal coverage with persistent ambient noise arrivals within three azimuthal quadrants - between 90 and 360 degrees. The highly coherent surface-wave retrieval and the wide azimuthal coverage of the microseisms explain the success of ANSI techniques in Iceland. For the tomographic inversion, we use a Tikhonov and a statistical regularisation to invert the ballistic surface-wave time-arrival to 3D frequency-dependent velocity variations. After further inversion to S-wave velocity variations, we detect low- and high-velocity anomalies with changes between -15% and 15% from an estimated average velocity, we interpret these anomalies as possible old dyke intrusions and heat sources.@en

We present first results of PS-InSAR (Persistent Scatterer by Synthetic Aperture Radar Interferometry) time-series over the eastern sector of the Trans-Mexican Volcanic Belt including several volcanic systems. The study area covers the Los Humeros and Acoculco geothermal fields. Los Humeros is one of the largest geothermal fields in Mexico connected to a caldera system that has been active from 0.46 Ma until recent. We performed PS time series analysis using the StaMPS method on Sentinel-1 images acquired between October 2016 and December 2017 to resolve ongoing ground deformation. The Sentinel-1 satellite provides regular observations with fine temporal resolution over large areas, which facilitates detection of satellite line-of-sight surface movements important for monitoring geothermal exploration activities. Generally, the interferograms are of good quality with high coherence even on long time scales. Most of the study area is located at high altitudes (above 2000 m) with strong relief. Asa result, the interferograms seem to be influenced by topography-related atmospheric phase delays, identified by the high correlation between phase and elevation. We correct the topography-related atmospheric phase delays and compare the InSAR estimated displacements with the available GPS data. Our goal is to obtain the deformation associated with ongoing geothermal activities over the Los Humeros geothermal field and other tectonic processes that might be present in the area. Here we present our first results, which will be further extended to estimate volume changes related with the geothermal exploration by inversion methods.@en

Variations of b-values in Gutenberg-Richter’s law has been proven to provide insights on earthquake triggering mechanisms. These b-value variations express changes in the rate of occurrence of small earthquakes relative to large ones. Geophysical processes correlated with b-value variations have been identified using earthquake catalogues over natural tectonically active environments. Not so much is known over anthropogenic exploration sites due to the lack of dedicated seismometers in place and therefore the reduced number of recorded events. In the early 1990's, nearly after 30 years of gas production, small seismic events started to be detected at the Groningen gas field. Several efforts to measure these seismic events let to a unique seismic network and an earthquake catalogue available through KNMI’s website. We perform a temporal, spatial and spatiotemporal b-value analysis for which we use 800 events from early 90’s up to now with a magnitude lower limit of 1.1 (magnitude of completeness).@en

In recent years, new algorithms have been proposed to retrieve maximum available information in synthetic aperture radar (SAR) interferometric stacks with focus on distributed scatterers. The key step in these algorithms is to optimally estimate single-master (SM) wrapped phases for each pixel from all possible interferometric combinations, preserving useful information and filtering noise. In this paper, we propose a new method for SM-phase estimation based on the integer least squares principle. We model the SM-phase estimation problem in a linear form by introducing additional integer ambiguities and use a bootstrap estimator for joint estimation of SM-phases and the integer unknowns. In addition, a full error propagation scheme is introduced in order to evaluate the precision of the final SM-phase estimates. The main advantages of the proposed method are the flexibility to be applied on any (connected) subset of interferograms and the quality description via the provision of a full covariance matrix of the estimates. Results from both synthetic experiments and a case study over the Torfajökull volcano in Iceland demonstrate that the proposed method can efficiently filter noise from wrapped multibaseline interferometric stacks, resulting in doubling the number of detected coherent pixels with respect to conventional persistent scatterer interferometry.

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Torfajökull is the largest silicic volcanic centre in Iceland lying at the intersection of the rift zone (MidAtlantic Ridge) and the transform zone that connects to Reykjanes peninsula. It erupts infrequently,with only two eruptions in the last 1200 years, the latest of which was over 5 centuries ago. Yet, itsactive tectonic setting, persistent high and low frequency seismicity, deformation and geothermalactivity within its large caldera (18x12 km diameter) indicate the continued presence of a long-lasting magma chamber. Here we speculate on possible geometry, size and depth of the Torfajökullmagma chamber by using radar interferometry (InSAR) and seismic interferometry (SI).Using InSAR time series analysis we detect a surface subsidence pattern at rates of up to ~13 mm yr-1in the SW region of Torfajökull ́s caldera, on-going since at least 1993. The subsidence rate isconstant in time, and perhaps due to a cooling magma chamber. The data can be fit reasonably wellusing a model of a NE-SW oriented spheroidal body at ~5 km depth. As the deflating area correlatesspatially with the area of geothermal activity, deflation may also be the surface response due to anactive hydrothermal circulation.To gain more insight into the geometry of Torfajökull’s magmatic system and rock properties of thesubsurface, we apply ambient noise seismic interferometry (SI) by cross-correlation of ambient noise.With this technique we can detect velocity variations, which can correspond to the edges of dikes ormolten magma bodies. Our tomographic results give reliable results of velocity variations within adepth range of 2 km to 7.5 km. We find high velocity zones that we interpret as old dike intrusions.Low velocity anomalies (>5%), which usually indicate the presence of warmer material, are locatedon the southeast and southwest part of the volcano, outside the volcano caldera.Finally we compare both InSAR and SI results. The hypothesis of a magma chamber under thesubsidence area detected by InSAR does not seem to fit the tomographic results, as the expectededges of a magma body modelled by InSAR are not clearly identified by the SI results. If there is anestablished magma chamber within Torfajökull caldera this is likely to be bellow 7km depth.@en

Magmatic plumbing systems beneath active and moderately active volcanoes are often poorly constrained. A better knowledge of the shape, size and location of the magma bodies would enable us to better predict magma movements preceding an eruption. Surface displacements estimated from radar interferometry (InSAR) can be used in geophysical modelling to constrain location, geometry and pressure changes in magma systems. However, the resolution of the inferred magma chamber is typically poor. More insight into the location and geometry of magmatic systems can be gained using active-source reflection seismic surveys, which allow detection of velocity contrasts at the edges of the magma bodies. The drawback of this technique is that controlled-source surveys are expensive. As an alternative, seismic interferometry (SI) uses cross-correlation of natural signals to generate new seismic records that simulate active sources. Under the premise that both seismic and radar observations would help to narrow down the location, shape and size of a magma system, we present the first results of combined radar and seismic interferometric processing over Torfajökull volcano. Torfajökull is located in the neovolcanic zone, in the south of Iceland. The volcano is characterized by intense thermal manifestations (hot springs forming ground steaming and fumaroles) with higher activity nearby the faults of the active NE-SW fissure swarm. Torfajökull erupts infrequently, with only two eruptions in the last 1200 years, the latest of which was over 5 centuries ago. However, ongoing seismicity, deformation and geothermal activity indicate the continued presence of a long-lasting magma chamber. Although historical eruptions have been relatively small, the large caldera (18x12 km diameter) and high geothermal activity within the caldera is evidence of a massive eruption in the past, and the potential for a further eruption of similar size is unknown. We applied InSAR time series analysis to data acquired by Envisat over the Torfajökull region along 6 different tracks (3 tracks in ascending and 3 tracks in descending mode). The estimated velocity maps show subsidence beneath the SW part of the caldera. This subsidence has been on-going since at least 1993, with rates of up to ~13 mm/yr. This has been interpreted as a cooling magma chamber, shrinking at linear rates. To obtain a rough approximation of the geometry and location of the source of subsidence we ran a forward model. The model suggest an ellipsoidal magma chamber within the volcano caldera with a NE-SW orientation and at ~5km depth. For the SI processing we use two types of natural signals: microseisms and local earthquakes. We use seismic data acquired in 2005 at 30 stations sparsely distributed around the Torfajökull area. Using microseisms, we divide the noise, recorded at two stations in portions of 1h, cross-correlate the corresponding portions and then sum the correlated results. The result is a retrieved surface-wave part of the Green’s function between the two stations. This is repeated between all stations. Careful assessment of the quality of the retrieved Green’s functions for small time windows allows analysis of the microseism noise. The results show that the microseisms are dominant in the NW-SE direction and the resulting retrieved surface waves propagate at ~3 km/s in the double-frequency microseism band. The retrieved surface waves between the stations will be used in tomographic inversion that will allow derivation of the 3D S-wave velocity distribution in the subsurface. We will then use these results to better constrain our magma source model, currently constrained only by InSAR. @en

After a period of quiescence since a sill intrusion in 1999-2000, a subtle deformation signal was again detected at Eyjafjallajökull, beginning in the summer of 2009, at a continuous GPS station on the southern flank. At our request the German Space Centre (DLR) immediately began tasking the TerraSAR-X satellite to acquire three SAR images every 11 days, giving a time series of SAR images prior to the eruption with unprecedented temporal sampling (although interrupted by snow during the winter).
Previously we modelled individual interferograms that showed that there was a large uplift signal. We modelled this as a series of sills and a dike with a total volume of ~0.05 km3. During the flank eruption, beginning on 20 March, no significant deformation is detected, but coinciding with the start of the explosive eruption on April 14, we detected subsidence centred on the caldera. What we modelled showed us that Eyjafjallajökull was an unusual which we modelled …. This deformation does not relate to pressure changes within a single magma chamber.
Here we extend our analysis InSAR time series covering full eruptive period. After correcting for DEM errors and reduction of atmospheric signal, we have found a number of signals that we interpreted in terms of magma movement. These magma movements are separately analysed in 3 phases: pre-eruptive (inflation), co-eruptive (no deformation) and post-eruptive (deflation).
The displacement time series from June 2009 to 4 February 2010 (pre-eruptive-phase) shows line-of-sight shortening on the southwest flank of about 2 cm. The displacement signal is present in a set of interferograms and it has a consistent behaviour in time, implying that it is not due to atmospheric contamination. We performed atmospheric stratification over the entire Interferogram (4 Feb 2010) to check how much of the signal correlated with the topography would disappear when removed. The correlation coefficient over the southwest flank is very small compared with the signal from the entire interferogram. We can say that in this area not much of the atmospheric effects related with the topography are present, suggesting that the signal could be deformation.
For the co/post-eruptive phases we calculated phase difference between nearby points to check their evolution in time. In the southeast flanks we observe deflation through all analyzed period, while in western flanks of the volcano we observe Inflation during effusive eruption, followed by deflation during explosive eruption, and a new inflation pattern between 05 June and 19 July that we cannot explain. In preliminary modelling we fit this post-eruptive phase with a pressure decrease of an ellipsoidal source, equivalent to a volume reduction of ~0.03 km3.
The limitations when analysing this dataset are mainly concerning the phase unwrapping performance through ice- and ash-covered areas. This is caused by decorrelation owing to ash cover where there is almost complete loss of coherence. We applied new methods to overcome these limitations. To improve point density over the scene, we combined PS (Persistent Scatterers) and SB (Small Baselines) methods. By combining highly coherent interferograms, the increase of distributed scatterers is clear and the phase unwrapping performance improved. To detect and correct non-systematic unwrapping errors, we calculated azimuth and range offsets. Additionally, because of the fact that L band has higher penetration, we processed ALOS images trough single interferogram analysis. By these means we were able to extract more of the deformation signal around decorrelated areas.
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Mapping magmatic plumbing systems beneath active and moderately-active volcanoes contributes to our understanding of how magma spreads up to the crust surface. Additionally, the time that magma takes to accumulate in the earth’s interior before an eruption could be better estimated if we knew in detail the shape, size and depth of the magma chamber. Radar interferometric observations can used to measure displacements associated with crustal deformation and to subsequently infer magma chamber features through geophysical modelling. This is normally applied to highly active volcanoes, or volcanoes with an eruption imminent. However, less is known about long-lasting magma chambers beneath volcanoes that have not erupted for centuries. In this study, we explore the magma systems of two different Icelandic volcanoes using InSAR time series. Eyjafjallajökull, which erupted in April 2010 and caused significant disruption to air traffic, had not erupted prior to that for nearly two centuries, and only three times in total in the previous 1200 years.In 1992 an increase of seismicity signalled a change from its previous low activity. InSAR- and GPS-derived models of Eyjafjallajökull from these last 20 years of unrest, show a complex network of sills and dikes rather than a single established magma chamber. In 1994 and 1999 two deformation episodes were modelled as sill intrusions between 4.5 and 6.5 km depth under the southeastern flank. Prior to the 2010 eruption, further sills intruded at similar depths. Shortly before the onset of eruption, one or more dikes propagated upwards and eventually reached the surface. Curiously, the source of deflation during the explosive eruption has a different location and geometry to the sills modelled in the pre-eruptive phases. Torfajökull, also erupts infrequently, with only two eruptions in the last 1200 years, the latest of which was over 5 centuries ago. However, ongoing seismicity, deformation and geothermal activity indicate the continued presence of a long-lasting magma chamber. InSAR time series show subsidence of the southwestern part of the caldera with rates of up to ~13 mm yr-1, which has been interpreted as a cooling magma chamber. Although historical eruptions have been relatively small, the large caldera (12 km diameter) is evidence of a massive “supervolcano” eruption in the past, and the potential for a further eruption of similar size is unknown. Here we compare and contrast the two volcanoes and explore what we might expect in terms of warning signals in the case of a future eruption of Torfajökull. @en

After a period of quiescence since a sill intrusion in 1999-2000, a subtle deformation signal was again detectedat Eyjafjallajökull, beginning in the summer of 2009, at a continuous GPS station on the southern flank. At ourrequest the German Space Centre (DLR) immediately began tasking the TerraSAR-X satellite to acquire threeSAR images every 11 days, giving a time series of SAR images prior to the eruption with unprecedented temporalsampling (although interrupted by snow during the winter). Here we present the results of InSAR time seriesanalysis of this data set. After correcting for DEM errors and reduction of atmospheric signal, we find a numberof signals that we interpret in terms of magma movement.The displacement time series from June 2009 to 4 February 2010 (pre-eruptive-phase) shows line-of-sight short-ening on the south-west flank of about 2 cm. The signal shows a largely linear behaviour and is smooth in time,implying that it is not due to atmospheric contamination. The signal seems consistent with the nearby continuousGPS station THEY. We therefore interpret it as due to the intrusion of magma to shallow depths. Superimposed onthis uplift signal are two periods of subsidence, in August and November 2009, perhaps representing redistributionof the intrusion.Between 4 February and 20 March 2010 there is a large uplift signal which we model as a series of sills and a dike,with a total volume of∼0.05 km3 During the flank eruption, beginning on 20 March, no significant deformationis detected, but coinciding with the start of the explosive eruption on April 14, we detect subsidence centredon the caldera. The subsidence proceeds in an approximately steady-state fashion until the end of the eruption.In preliminary modelling we fit this with a pressure decrease of an ellipsoidal source, equivalent to a volumereduction of∼0.03 km3.@en

Persistent Scatterer Interferometry (PSI) has emerged over the last decade as a technique capable of very accurate (millimetric) measurements of ground deformation occurring at radar scatterers (persistent scatterers or PS) that are phase coherent over a period of time. PSI studies using C-band SAR data have shown that the PS spatial density in urban areas is usually very high (100-300 PS/km2). However, many ground deformation phenomena (e.g. tectonic motion, volcanoes, landslides, mining, gas extraction, CO2 sequestration) occur in uninhabited or rural areas with few man-made structures, leading to much lower PS density because of significant phase decorrelation between subsequent SAR acquisitions. In order for PSI to be effective in monitoring these areas, it has been found that a PS density greater than about 10 PS/km2 is required. Artificial amplitude- and phase-stable radar scatterers may thus have to be introduced in non-urbanised geodynamic areas that have too low a density of PS points. Conceptually the simplest of these artificial PS points are corner reflectors. Several experiments have been performed in the past using these reflectors, with conclusive results about their amplitude and phase stability. They suffer, however, from the disadvantage of large size (in the order of a metre in case of C-band SAR). To make these artificial PS points easy to deploy and maintain, especially in poorly accessible areas, Compact Active Transponders (CATs) have been designed to be used in lieu of corner reflectors. These CATs are small (in the order of a few tens of centimetres), lightweight (<3 kg), less obtrusive, and have the added advantage of a better link budget due to signal amplification by the transponder. They are sealed, function autonomously with internal power and over a wide temperature range, and can operate unattended for more than a year. Additionally, since a CAT is transmitter-specific and is only turned on at the time of the satellite overpass, it offers little interference to other radar or radio targets. However, it is of paramount importance in geodetic applications to ensure that the phase of the CAT remains stable in all operating and environmental conditions. Towards this goal, an experiment to validate the phase stability of CATs has been set up in a farmland in Delft (The Netherlands). The setup comprises three CATs and three corner reflectors, which are installed at distances of a couple of hundred metres from each other. SAR data from the ERS-2 Ice-Phase Mission are being acquired every three days between March and June 2011. Since the area does not exhibit steady ground deformation, some of the units are displaced vertically by a controlled amount. Levelling is performed between the CATs and the corner reflectors as close as possible to each SAR acquisition, in order to validate the height differences obtained from the radar phase information. As a second means of validation, campaign-style GPS is performed on each of the devices to accurately position them in WGS-84 coordinates. One of the CATs in the Delft field experiment has an integrated GPS antenna, to ensure millimetric coregistration and a coherent cross-reference. This novel unit called I2GPS (Integrated Interferometry and GNSS for Precision Survey) has been developed with the objective of producing a fully-integrated deformation map. In addition to providing absolute calibration for PSI data, the high temporal sampling rate of GPS data imparts the capability of accurately detecting abrupt ground motion in three dimensions. With adequate GPS/I2GPS units, the vertical components of the local velocity field can be derived from single-track InSAR line-of-sight displacements. The results and conclusions of this experiment consisting of corner reflectors, CATs and I2GPS will be presented and analysed here.@en

Detecting a point-like target when it is horizontally displaced is of paramount importance in target tracking and in measuring the motion of glaciers over short intervals of time. This paper performs an experimental study of the accuracy, precision and sensitivity of the horizontal motion detectable using SAR. Therefore point-like targets such as corner reflectors (CR) are moved horizontally in a controlled manner over short time intervals to reproduce the real target motion. Such CR movements are monitored using SAR and the results are compared with the ground truth to arrive at the target horizontal motion determination parameters. Towards this goal three CRs were installed each displaced by a few hundreds of metres in a farmland in Delft, The Netherlands. These corner reflectors are inclined for ERS-2 3-days ice-phase mission starting March 2011. Since the area does not exhibit horizontal motion, one of the CRs was moved horizontally stepwise in the order of a few centimeters to a few metres. At each step the CRs are imaged by SAR and also measured by campaign-style GPS (and with a few leveling campaigns) in order to provide the actual displacement in three dimensions. Then the motion is computed using SAR data and results are compared with the GPS measurements to validate the sensitivity of SAR in detection of motion of the targets. The experimental setup is such that the CRs are visible starting from March 2011 from both ascending and descending orbit TerraSAR-X satellite acquisitions over Delft. Hence similar parameters such as sensitivity, precision and accuracy of motion detection will be derived for X-band SAR as well. Further, in order to substantially verify the reliability of our computations, data from three different field experiments with stable CRs performed with ERS-1/2 in 1996, with ENVISAT from 2003 to 2007 and with ENVISAT from March 2010 to January 2011 in the areas of Groningen, Delft and Cabauw respectively were exploited. The outcome of our experiment will result in the empirical study of the sensitivity of motion detection of point-like targets in C- and X- bands. Also the influence of these parameters under varying imaging conditions such as change in Doppler and perpendicular baselines will be discussed. @en

The 2010 eruption of Eyjafjallajökull volcano and the resulting ash cloud highlights the need for research on Icelandic volcanoes. While most of the interest was sparked by the closure of air space over much of Europe, the potentially life-threatening consequences for the people living in the area directly beneath the volcano alone are incentive enough to better understand volcanic processes. Katla volcano is directly adjacent to Eyjafjallajökull volcano, and historically has been more active and produced larger eruptions. The consequences of an eruption at Katla could therefore be much more severe than those witnessed this spring at Eyjafjallajökull. Timely prediction of an impending eruption would greatly reduce the severity of these consequences, which is one of the ultimate goals of volcanic research. After a period of quiescence since a sill intrusion in 1999-2000, a subtle deformation signal was again detected at Eyjafjallajökull, beginning in the summer of 2009, at a continuous GPS station on the southern flank. We immediately began tasking the TerraSAR-X satellite to acquire SAR images every 11 days, giving a time series of SAR images prior to the eruption with unprecedented temporal sampling (although interrupted by snow during the winter). Here we present the results of InSAR time series analysis of this data set. After correcting for DEM errors and reduction of atmospheric signal we find a number of signals that we tentatively interpret as a combination of magma movement, elastic response to snow melting and landsliding.. The mean velocities from June 2009 to February 2010 show a subsidence pattern in the southeastern part of the volcano flanks and uplift in the southwest. However, such a different deformation signal between two areas so close could also imply atmospheric, topographic or phase unwrapping errors. To assess the contribution to the deformation signal from these possible error sources, we examined time series of displacements during this period for various areas. The results show a largely linear behavior between nearby areas from 18th June 2009 to 04 February 2010, followed by an excursion in the deformation signal during 17th October 2009. Significantly, the signal is smooth in time, implying that it is not due to atmospheric contamination. The deformation seems consistent with the continuous GPS station THEY, and can indeed indicate magma migration. However, further work is required to reliably separate out the deformation signals that are not related to volcanic processes.@en

The proposal for a Program for the requalification of Lisbon's "priority intervention Neighborhoods or Zones" (hereon, BIP/ZIP, original acronym in Portuguese) comes within the scope of the objectives of the Local Housing Program (PLH), approved by the autarchic bodies at the end of 2009. The first task implied the construction of the concept of Priority Intervention Neighborhood, which was worked on the definition of "Critical Neighborhood" (Resolution of the Council of Ministers 142/2005 of August 2), in conjunction with the research of socio- economic, urban and environmental. It was then moved to a finer definition, which includes not only Priority Intervention Districts (BIPs), but also Priority Intervention Zones (ZIP). As a first approach to the BIP / ZIP delimitation, several existing municipal boundaries that could be included in the Priority Neighborhood concept and that had already been identified within the scope of the PLH were transposed to cartographic support. The delimitations considered were as follows: 1.ACRRU - Critical Area of Urban Recovery and Reconversion 2. AUGI - Urban Area of Illegal Genesis 3. Municipal Districts (under GEBALIS management) with special problems 4. Remaining Areas of PIMP and PER (Special Rehabilitation Programs) 5. Neighborhoods ex-SAAL with serious problems pending 6. Area of intervention of the Western SRU - Western Urban Rehabilitation Assistance 7. Area of intervention of the Viver Marvila Program As a second approach to the BIP / ZIP delimitation, the following analytical method was used: several relevant indicators were selected to identify the most critical situations in the socio-economic, urban and environmental dimensions, which allowed the construction of a social index and an urban index with graphic expression at the block scale (statistical subsection). The cartographic analysis was complemented with data to the scale of the parish. It was not possible, with the available data, to build an environmental index. The social index and the urban index were worked together, duly filtered, allowing the creation of a composite index that synthesizes the most critical occurrences in the socioeconomic and urbanistic dimensions. From the cartographic overlap of this composite index with the municipal boundaries already analyzed, it results in the determination of a "spot" in the city that defines its socio-territorial fracture, thus showing the areas of the city where, more likely, are the neighborhoods and zones intervention. On this spot was made an empirical first identification of 50 neighborhoods. The methodology used and the list of neighborhoods identified were subject to three participatory workshops, involving municipal services and companies, permanent committees of the Municipal Housing and Urban Planning Council, parish councils and associations of residents of the identified neighborhoods. in the end, an extension of the initial list to the current 6 61 Districts and Priority Intervention Areas included in the C Letter of the BIP-ZIP approved by the CML for submission to public consultation until September 30.@en