ERS-1 Satellite Research Articles

A Case Study of Wave–Wave Interaction South to Dongsha Island in the South China Sea

In a SAR image acquired by the ERS-2 satellite, crossed “X-shape” internal solitary waves (ISWs) south to Dongsha Island are found to be a wave–wave interaction composed of five solitons: two head waves, two tail waves, and the overlapped part. To explain this remote sensing phenomenon, based on a high-resolution three-dimensional MIT general circulation model (MITgcm) using realistic topography and tidal forcing, the “X-shape” internal waves are reproduced at the same location. The development processes of the waves indicate that the “X-shape” ISWs are two waves diffracted from one internal wave southeast to Dongsha Island. During the propagation, the amplitude of their overlapped part of the “X-shape” ISWs becomes significantly larger than the sum of the amplitudes of both head waves, which proves that nonlinear wave–wave interaction has occurred. Based on wave–wave interaction theory, the theoretical maximum value of the amplitude of the overlapped part at the initial moment is calculated as 14.12 m, which is in good agreement with the model results of 14 m. Meanwhile, the variation of the theoretical amplitude of the overlapped part is basically consistent with that of the modeled one, confirming the occurrence of the wave–wave interaction. Besides, when the waves propagate over varying water depths, the type of the wave–wave interaction can change rather than being fixed from the start.

Observing decoupling processes of NO2 pollution and GDP growth based on satellite observations for Los Angeles and Tokyo

Nitrogen dioxide (NO2) pollution is mainly caused by anthropogenic processes such as burning of fossil fuels. Due to its severe impact on health as well as the environment in general, it is important to monitor the amount of NO2 pollution especially in areas with a high population density. Therefore, the aim of this study is to investigate to what extent spatiotemporal fluctuations in the tropospheric NO2 column density can map variations in economic output. To do so, we analyzed satellite based tropospheric NO2 column observations obtained from the ERS-2, ENVISAT, MetOp-A and MetOp-B satellite missions covering the period from 1996 to 2017 for Tokyo, Japan and Los Angeles, United States. Within our studies, a harmonic analysis was carried out in order to exclude meteorological influences. Afterwards, the NO2 time series were further investigated through a wavelet analysis method to characterize the fluctuations, that is the temporal variability of the NO2. These fluctuations have been shown to be a particularly sensitive measure of the change in NO2 pollution. We further use the gross domestic product (GDP) for the metropolitan areas as an indicator for economic performance. The results for the study area of Los Angeles shows a substantial reduction in NO2 variability starting in 2007. The NO2 variability for the period during the global financial crisis (December 2007–April 2012), dropped by around 77% in comparison to the previous period (January 1997–November 2007). However, a second period from May 2012 to December 2016 presents a further reduction of the NO2 variability of around 82% in contrast to the period from 2007 to 2012. Contrary to this, continuous economic growth can be observed during the second period. A similar picture emerges for the metropolitan region of Tokyo. A significant decline in NO2 variability of around 73% can be detected from October 2003 to January 2012. Additionally, a second period with a strong decline in NO2 variability of around 80% can be identified from February 2012 to December 2016. A plunge in GDP during 2008 reflects that year's global financial crisis, but cannot independently explain the following sharp decline in NO2 variability. Those results suggest that Tokyo as well as Los Angeles managed to substantially decouple its NO2 pollution from the economic growth due to strict air quality policies.

Post Mining Ground Deformations Transition Related to Coal Mines Closure in the Campine Coal Basin, Belgium, Evidenced by Three Decades of MT-InSAR Data

Spatio-temporal ground-movement measurements and mappings have been carried out in the Campine coalfield in Belgian Limburg since the closure of the mines to document post-mining effects. MT-InSAR measurements are compared to groundwater head changes in the overburden and to height data from the closest GNSS stations. Radar interferometry is used to estimate the extension and the velocity of ground movements. In particular, the MT-InSAR technique has been applied to SAR acquisitions of the satellites ERS-1/2 (1991–2005), ENVISAT (2003–2010), COSMO-SkyMed (2011–2014), and Sentinel-1A (2014–2022). The images were processed and used to highlight a switch from subsidence to uplift conditions in the western part of the coal basin, while the eastern part had already been affected by a rebound since the beginning of the ERS-1/2 acquisitions. Following the closure of the last active colliery of Zolder in 1992 and the subsequent cease of mine-water pumping, a recharge of mine-water aquifers occurred in the western part of the basin. This process provoked the change from subsidence to uplift conditions that was recorded during the ENVISAT period. In the center of the coal-mining area, measured uplift velocities reached a maximum of 18 mm/year during the ENVISAT period, while they subsided at −12 mm/year during the ERS-1/2 period. Mean velocities in the western and eastern parts of the coalfield area have decreased since the last MT-InSAR measurements were performed using Sentinel-1A, while the Zolder coal mine continues to rise at a faster-than-average rate of a maximum of 16 mm/year. The eastern part of the coalfield is still uplifting, while its rate has been reduced from 18 mm/year (ERS-1/2) to 9 mm/year (Sentinel-1A) since the beginning of the radar–satellite observations. Time-series data from the two GNSS stations present in the study area were used for a local comparison with the evolution of ground movements observed by MT-InSAR. Two leveling campaigns (2000, 2013) were also used to make comparisons with the MT-InSAR data. The station’s measurements and the leveling data were in line with the MT-InSAR data. Overall, major ground movements are obviously limited to an extension of the actual underground-mining works and rapidly diminish outside of them.

Neural Network Pattern Recognition Experiments Toward a Fully Automatic Detection of Anomalies in InSAR Time Series of Surface Deformation

We present a neural network-based method to detect anomalies in time-dependent surface deformation fields given a set of geodetic images of displacements collected from multiple viewing geometries. The presented methodology is based on a supervised classification approach using combinations of line of sight multitemporal, multi-geometry interferometric synthetic aperture radar (InSAR) time series of displacements. We demonstrate this method with a set of 170 million time series of surface deformation generated for the entire Italian territory and derived from ERS, ENVISAT, and COSMO-SkyMed Synthetic Aperture Radar satellite constellations. We create a training dataset that has been compared with independently validated data and current state-of-the-art classification techniques. Compared to state-of-the-art algorithms, the presented framework provides increased detection accuracy, precision, recall, and reduced processing times for critical infrastructure and landslide monitoring. This study highlights how the proposed approach can accelerate the anomalous points identification step by up to 147 times compared to analytical and other artificial intelligence methods and can be theoretically extended to other geodetic measurements such as GPS, leveling data, or extensometers. Our results indicate that the proposed approach would make the anomaly identification post-processing times negligible when compared to the InSAR time-series processing.

Comparison between economic growth and satellite-based measurements of NO2 pollution over northern Italy

The aim of this study is to investigate to what extent spatiotemporal fluctuations in the tropospheric NO2 column concentration can map variations in economic output. To do so satellite based tropospheric NO2 column measurements obtained from the ERS-2, ENVISAT, MetOp-A, and MetOp-B satellite missions covering the period from 1996 to 2017 over the Po valley in northern Italy is analyzed. A harmonic analysis is carried out in order to exclude influences such as the annual or semi-annual cycle. Afterwards the residues of the tropospheric NO2 time series are further investigated by means of a wavelet analysis method. The result is a spectrogram which implies the NO2 variability for the study area between 1996 and 2017. Therefore, the gross domestic product (GDP) is used as an indicator for economic performance and thus, as an approximation, of anthropogenically induced NO2 pollution. Clear conspicuous signatures occurred almost simultaneously both within the temporal development of the GDP growth rate and the spectral characteristic of the NO2 variability during the studied period. The comparison of the temporal course of the GDP shows that the period of systematically reduced spectral intensity in NO2 coincides strikingly well with the period of the global financial crisis in 2008 which was then followed by a second crisis in 2014. The economic growth decreased by 7.9% between 2007 and 2009 and by 5.2% between 2011 and 2014 in comparison to the same quarter of the previous year. It is found that during the crises (2007–2013) the variability of NO2 is reduced by about 80%.

Staggered Coprime Pulse Repetition Frequencies Synthetic Aperture Radar (SCopSAR)

High-resolution wide-swath synthetic aperture radar (HRWS-SAR) imaging is highly desirable since it allows one to produce high-resolution SAR images of large areas during a short visit time. In this article, staggered coprime pulse repetition frequencies synthetic aperture radar (SCopSAR) is proposed. It divides the time during which a scatterer is illuminated by the antenna beam pattern into two halves where, in each half, pulses are transmitted at the rate of one of two sub-Nyquist pulse repetition frequencies (PRFs). Such PRFs are related to the Nyquist PRF using two coprime subsampling factors. This allows extending the maximum range swath width that can be imaged by a number of times that equals the smaller subsampling factor at the expense of a reduction in the azimuth resolution by half. It further allows for a reduction in the amount of data to be stored and communicated. SCopSAR is an imaging modality suitable for scenes that contain a small number of bright scatterers over a dark background which, for instance, is the case when imaging ships in a calm sea background. Compared with the techniques recently proposed in the literature, SCopSAR simplifies the radar requirements since it uses only one carrier frequency, one waveform, and one channel. Simulations and real ERS-2 satellite raw data are used to validate the theoretical findings presented in this article.

Evolution of Deep-Seated Gravitational Slope Deformations in Relation with Uplift and Fluvial Capture Processes in Central Eastern Sardinia (Italy)

Connections between Plio-Pleistocenic tectonic activity and geomorphological evolution were studied in the Pardu Valley and Quirra Valley (Ogliastra, East Sardinia). The intensive Quaternary tectonic activity in Sardinia linked to the opening of the Tyrrhenian Basin is known. In Eastern Sardinia, it manifests with an uplift that is recorded by geomorphological indicators, such as deep-seated gravitational slope deformation, fluvial captures, engraved valleys, waterfalls, and heterogeneous water drainage. The Pardu River flows from the NW toward the SE and then abruptly changes direction toward the NE. At this point, a capture elbow adjacent to the current head of the Quirra River is well developed. The Quirra River, in its upstream part, flows at altitudes approximately 200 m higher than the Pardu River. It also shows an oversized and over-flooded valley with respect to the catchment area upstream. This setting indicates that the Pardu River, which previously flowed south along the Quirra River, was captured by the Pelau River. We analyzed long-term landslides with lateral spreading and sackung characteristics, which involve giant carbonate blocks and underlying foliated metamorphites in both valleys. The use of LiDAR, high-resolution uncrewed aerial vehicle digital photogrammetry (UAV-DP), and geological, structural, and geomorphological surveys enabled a depth morphometric analysis and the creation of interpretative 3D models of DGSDs. Space-borne interferometric synthetic aperture radar (InSAR) data using ERS and Sentinel-1 satellites identified downslope movement of up to 20 mm per year in both Pardu Valley flanks. Multi-source and multi-scale data showed that the state of activity of the DGSDs is closely linked to the geomorphological evolution of the catchment areas of the Rio Pardu and Rio Quirra. The intense post-capture erosion acted in the Rio Pardu Valley, giving it morphometric characteristics that were favorable to the current evolution of the DGSDs, while the Rio Quirra Valley presents paleo-DGSDs that have been fossilized by pre-capture terraced alluvial deposits.

Long term displacement observation of the Atatürk Dam, Turkey by multi-temporal InSAR analysis

Monitoring large infrastructures is vital for determining structural safety over time. Dams are structures that influence agricultural activities and have high economic contributions. The dams' structural safety was mainly addressed using conventional measurement techniques. However, these might not be time-efficient and practical, considering the large surfaces of dams. This paper presents a long-term InSAR analysis of the Atatürk Dam, Turkey's largest and one of the five biggest dams in Europe using ERS, ENVISAT, and Sentinel-1 satellites images. Since only Sentinel-1 data have acquisitions in ascending and descending orbits, we could estimate surface movements also in the vertical and east-west directions using both lines of sight (LOS) displacements. The results showed that the east-west movement is higher than vertical movement. As a result, we observe a maximum of 10 mm/yr displacement in the LOS direction at the dam's crest for period of 2003 and 2010, decreasing down the slope.

Ground motion baseline analysis of the Cheshire UK GeoEnergy Observatory

Subsurface geonergy can induce ground motion and seismicity, however a scarcity of observations usually obscures the mechanisms underpinning such behaviour. Here, we analyse Interferometric Synthetic Aperture Radar (InSAR) data from ERS, ENVISAT and Sentinel-1 satellites for the period 1995–2017 and interpret ground deformation in the area of the planned Cheshire UK GeoEnergy Observatory ahead of facility contruction. Ground motion is dominated by the compaction of tidal flat deposits overlying two paleo-valleys, trending NNW–SSE. The western paleo-valley experienced faster subsidence rates in the period 1995–2007, whereas the eastern paleo-valley subsided faster in the period 2016–2017. The research highlights how baseline assessment can help differentiate natural variation from any anthropogenic effects associated with the growth of new subsurface technologies.

Conceptual scenarios for development of ground infrastructure for receiving mission payload data from a perspective Earth remote sensing satellite constellation

In view of the considerable number of elements in space and ground segments of a heterogeneous space ERS system, a mechanism is required for developing its concepts with obtaining refined baseline data for determining measures to optimize the ERS ground segment configuration geography-wise and outfit receiving systems for receiving mission payload data from high-performance ERS satellites. The development trends for equipment and technologies for mission payload data are given, in particular the status of the high backbone network in order to determine possible locations for of a space ERS system. Indicators are introduced which the capabilities of a wide-area network of remote sensing ground transmitting ERS data rate optical segment elements systemically characterize data receiving stations. Based on the obtained data, system-level patterns were determined in the development of the ground segment for receiving the ERS mission payload data depending on the state of the ERS satellite constellation, driving further development of strategy for the ERS ground infrastructure.

Long-term retrospective investigation of a large, deep-seated, and slow-moving landslide using InSAR time series, historical aerial photographs, and UAV data: The case of Devrek landslide (NW Turkey)

This study presents a successful combination of different remote sensing data used in a long-term retrospective investigation of a large and destructive deep-seated, slow-moving landslide reactivated on 16 July 2015 in Devrek District (Zonguldak, Turkey). To this aim, Synthetic Aperture Radar (SAR) data were used for Interferometric SAR (InSAR) time-series analysis together with unmanned aerial vehicle (UAV) images and aerial photographs for digital photogrammetric analysis. The SAR dataset was divided into three sub-periods: 1) 1992–2001 for ERS-1 and ERS-2 satellites; 2) 2003–2010 for Envisat ASAR; and 3) 2014–2015 for Sentinel-1. Persistent Scatterers Interferometry (PSI) was applied for each sub-period. In total, 20 aerial photographs, dating from as early as 1944, were obtained, along with data from a UAV flight mission conducted on 23 June 2018. The historical aerial photographs revealed that the region has had a landslide problem since the 1940s. Between 1944 and 2018, a noticeable expansion of the settlement area towards the toe of the landslide was also observed. Aerial photographs (1984 and 2011) and UAV images (2018) were used to map landslide deformations using the M3C2 algorithm. Due to the high number of modelling errors, the 1984 and 2011 aerial photographs did not allow mapping of the landslide deformations. However, it was possible to determine them for the periods of 2011 and 2018. The M3C2 results between 2011 and 2018 were also compared to the PSI results, which were quite compatible with those obtained via photogrammetric methods. Moreover, two orthophotos belonging to 2011 and 2018 were used to reveal the horizontal displacement of buildings caused by the landslide. As a result, the complete investigation of the landslide performed in this study may serve to facilitate additional plans and strategies for prevention and mitigation of potential reactivations in the future.

A deformation study of Anthemountas graben (northern Greece) based on in situ data and new InSAR results

The focus of this study is Anthemountas basin in northern Greece, where land subsidence phenomena had been previously identified. The basin has a NNW-SSE orientation, which is optimal to the currently acting ~ N-S extension field in the back-arc Aegean area and is bordered to its north and south edge by two, well-pronounced faults. The region of study is located close to the greater metropolitan city of Thessaloniki and comprises a number of critical facilities including the city’s international airport. The research object is the monitoring of the evolution of the displacement at Anthemountas graben, using InSAR time-series and the investigation of the dominant driving mechanism. We show new surface displacement results from the ENVISAR satellite, and overall, an enhanced dataset of SAR time-series is presented, spanning the period 1992 to 2010, by using the satellites ERS1, ERS2 and ENVISAT. Results indicate a continuously deforming environment in both decades, with an increasing magnitude. The detailed study of the deformation pattern together with the analysis of in situ data defines aquifer overpumping as the main cause of the detected displacement of both decades. Critical regions are examined in detail, as for example: an area close to Thermi, the town of Perea and the Thessaloniki’s international airport, a major hub of the Balkans. The latter was subjected to an increasing deforming velocity during the monitoring period. Overall, we conclude that a water management plan should be of high priority for the area.

Consolidating sea level acceleration estimates from satellite altimetry

More than 27 years of high precision satellite altimetry enables analysis of recent changes in global mean sea level (GMSL). Several previous studies present estimates of the trend and acceleration in GMSL; however, all are exclusively performed with data from the TOPEX/Poseidon, Jason-1, Jason-2 and Jason-3 missions (TPJ data). In this study we extend the altimetry record in both time and space by including independent data from the ERS-1, ERS-2, Envisat and CryoSat-2 missions (ESA data). This increases the time-series to span more than 27 years (1991.7–2019.0) and the spatial coverage is extended from ± 66° to ± 82° latitude. Another advantage of the ESA data is that it is independent of the issues associated with the TOPEX altimeter which introduce a significant uncertainty to the first part of the record. GMSL based on ESA data on the 1991–2019 period within ± 82° latitude exhibit an acceleration of 0.095 ± 0.009 mm/yr2. The corresponding value for the TPJ data is 0.080 ± 0.008 mm/yr2 for the 1993–2019 period and within ± 66° latitude. The ERS-1 satellite was launched shortly after the large Pinatubo eruption in 1991. The satellite observes a decrease of 6 mm in GMSL during the first 1.7 years until the launch of TOPEX/Poseidon. The distribution of sea level acceleration across the global ocean is highly similar between the ESA and TPJ dataset. In the Pacific Ocean regional sea level acceleration patterns seem related to the El-Niño Southern Oscillation (ENSO) whereas around Greenland a clear negative acceleration is seen.

Efficient Use of Satellite Gravity Anomalies for mapping the Great Sumatran Fault in Aceh Province

<p>Gravity Satellite has been widely used in tectonic studies and regional of geological mapping. The Satellite Gravity data are provided free by Scripps Institution of Oceanography, University of California San Diego. The data are acquired by GEOSAT and ERS-1 satellites with a 1.5 km resolution for one pixel. For a further application, the tilt derivative analytic technique was used in order to enhance linear trends of the geological structure revealed by the Bouguer anomalies. The method is represented by the value of an angle between the total horizontal and vertical derivative from the gravity data. The results show that the tilt derivative calculation has been able to map clearly some geological structures on the north of Sumatra i.e., the Aceh and the Seulimeuem segments, as well as some local faults around them. On the other hand, Banda Aceh as the capital city of Aceh Province and Pidie District is dominated by positive values of the tilt derivative anomalies. The data coincide with geological maps of both areas where they are covered by alluvial deposits. Based on the result, it can be concluded that the tilt derivative method is potentially used for quick interpretation of the satellite gravity data.</p>

Analysis and Classification of Natural and Human-Induced Ground Deformations at Regional Scale (Campania, Italy) Detected by Satellite Synthetic-Aperture Radar Interferometry Archive Datasets

The high levels of geo-hydrological, seismic, and volcanic hazards in the Campania region prompted full data collection from C-band satellites ERS-1/2, ENVISAT, and RADARSAT within regional (TELLUS) and national (PST-A) projects. The quantitative analysis, interpretation, and classification of natural and human-induced slow-rate ground deformations across a span of two decades (1992–2010) was performed at regional scale (Campania, Italy) by using interferometric archive datasets, based on the Persistent Scatterer Interferometry approach. As radar satellite sensors have a side-looking view, the post-processing of the interferometric datasets allows for the evaluation of two spatial components (vertical and E-W horizontal ones) of ground deformation, while the N-S horizontal component cannot be detected. The ground deformation components have been analyzed across 89.5% of the Campania territory within a variety of environmental, topographical, and geological conditions. The main part (57%) of the regional territory was characterized during 1992–2010 by stable areas, where SAR signals do not have recorded significant horizontal and vertical components of ground deformation with an average annual rate greater than +1 mm/yr or lower than −1 mm/yr. Within the deforming areas, the coastal plains are characterized by widespread and continuous strong subsidence signals due to sediment compaction locally enhanced by human activity, while the inner plain sectors show mainly scattered spots with locally high subsidence in correspondence of urban areas, sinkholes, and groundwater withdrawals. The volcanic sectors show interplaying horizontal and vertical trends due to volcano-tectonic processes, while in the hilly and mountain inner sectors the ground deformation is mainly controlled by large-scale tectonic activity and by local landslide activity. The groundwater-related deformation is the dominant cause of human-caused ground deformation. The results confirm the importance of using Persistent Scatterer Interferometry data for a comprehensive understanding of rates and patterns of recent ground deformation at regional scale also within tectonically active areas as in Campania region.

Evaluation of functional expectations of thematic consumers from optical space remote sensing systems of medium resolution

According to the results of direct interaction with various groups of consumers, it was established that the structure of requirements in all thematic areas at the present time comes to the fore geographic coverage, regularity and frequency of shooting. The second priority is to ensure the quality of the spectroradiometric characteristics in the context of their absolute performance and stability in the time series of the entire archive of the survey with the ability to provide data in physical quantities of reflectivity, or spectral brightness of the reflected radiation / brightness temperature. The requirements for spatial resolution within a separately allocated class of data, as well as the presence of a panchromatic channel are not significant for the majority of respondents. In the understanding of thematic users, the mediated requirements for the characteristics of the target remote sensing equipment are formed through direct requirements for the initial remote sensing data. When creating a promising ERS satellite on the part of the state customer, it is advisable to conduct regular advanced studies of user expectations and preferences in order to fully coordinate and integrate them into technical specifications for various products of the space system. In general, for effective generalization of various, often opposite, functional expectations, it is advisable to conduct a comprehensive discussion that provides a feedback mechanism from both authorized representatives of main consumers and developers of target equipment and space remote sensing systems.

A LISFLOOD-FP hydraulic model of the middle reach of the Congo

In this paper we attempt to produce a first hydrodynamic model of the middle reach of the Congo river system in order to understand what controls this river’s unique bimodal flood pulse. The model covers the area between Kisangani and Kinshasa on the main stem and includes the major tributaries and the Cuvette Centrale wetland, one of the world’s largest and most understudied lowland regions. A mixture of in-situ discharges and modelled discharge from a basin-wide catchment hydrology model were used to force a four-kilometre resolution hydrodynamic simulation developed using the LISFLOOD-FP model. River channels are represented as sub-grid scale features and their width is therefore decoupled from that of the over-lying floodplain grid. Unknown channel friction and bathymetry parameters were calibrated using ERS-2 and Envisat satellite altimetry measurements of channel water level. The calibrated model simulated channel water surface elevations across the domain with a bias and root mean square error of 0.185 and 0.842 m respectively. The value for root mean squared error is close to that obtained for comparisons of ERS-2 and Envisat satellite altimetry to in-situ water elevation data in similar basins (0.79 m and 0.47 m respectively). The model results imply that the bimodal annual pattern of Congo river discharge is predominantly a hydrological rather than hydraulically-controlled feature, with the channel-floodplain interactions and river constrictions having only a modest impact on the flood wave propagation. Nevertheless, and counter to current understanding, we find that interactions between channels and floodplains do however occur extensively, with over 2100 km of the 13,000 km of channel network in the model identified as zones where water is actively exchanged between channels and floodplains. Whilst the water volume that is exchanged with the floodplain is substantially less than for other large rivers, our results imply that channel-floodplain interactions are a significant feature of Congo flood wave propagation. Overall the model provides insights into the hydraulics of this understudied system that can next be tested both in the field and through more detailed modelling studies.

From Picture to Movie: Twenty Years of Ground Deformation Recording Over Tuscany Region (Italy) With Satellite InSAR

Synthetic Aperture Radar Interferometry (InSAR) techniques have been long exploited for detecting and mapping slow-moving ground surface displacements due to their millimetre accuracy, non-invasiveness and wide area coverage. A review on different applications of Persistent Scatterers InSAR approaches, proposed and applied over Tuscany region (Italy) across time, is here presented. The study area is characterized by both subsidence of alluvial plains and landslides on hilly and mountainous reliefs. Tuscany has a leading role in Italy in the field of interferometric applications: the first InSAR analysis, which date back to 2003, have been performed at local basin scale, by exploiting various PSI-based approaches for risk mapping. First InSAR applications at regional scale date back to 2009, relying on historical SAR archives of ERS and ENVISAT satellites for updating subsidence and landslide inventory maps at a certain temporal date. Nowadays, the availability of Sentinel-1 SAR data with a regular and systematic 6-days acquisitions plan, allows a near-real time monitoring of deformative scenario at regional scale rather than a solely mapping of geo-hydrological phenomena. Last innovative InSAR applications over Tuscany region scan the territory, exploiting the regular repeat pass of Sentinel-1, and promptly highlight the sites affected by the highest ground movements with high temporal frequency. Such approach permits to pass from a static ‘picture’ of the regional slope instability up to a weekly-updated ‘movie’ with improved detail, useful for civil protection practices. These last ongoing works significantly enhance the value of multi-temporal InSAR approaches for investigating and managing geo-hazards over the Region.

The Locking Depth of the Cholame Section of the San Andreas Fault from ERS2-Envisat InSAR

The Cholame section of the San Andreas Fault (SAF), which has been considered locked since 1857, has been little studied using geodetic methods. In this study, we propose to use Interferometric Synthetic Aperture Radar (InSAR) to contribute to the improvement of the knowledge of this section of the SAF. In particular, the objective of this work is to provide a description of the transition between the Parkfield and Cholame-Carrizo segments further southeast by producing an estimate of the locking depth of the Cholame segment by combining ERS2 (European Remote Sensing) and Envisat Advanced SAR (ASAR) satellites data. Our results indicate that the locking depth between the Parkfield and the Cholame-Carrizo segments deepens to the southeast. We then use these results as a hint to refine the tectonic loading on this section of the SAF.

Analysis of Secular Ground Motions in Istanbul from a Long-Term InSAR Time-Series (1992–2017)

The identification and measurement of ground deformations in urban areas is of great importance for determining the vulnerable parts of the cities that are prone to geohazards, which is a crucial element of both sustainable urban planning and hazard mitigation. Interferometric synthetic aperture radar (InSAR) time series analysis is a very powerful tool for the operational mapping of ground deformation related to urban subsidence and landslide phenomena. With an analysis spanning almost 25 years of satellite radar observations, we compute an InSAR time series of data from multiple satellites (European Remote Sensing satellites ERS-1 and ERS-2, Envisat, Sentinel-1A, and its twin sensor Sentinel-1B) in order to investigate the spatial extent and rate of ground deformation in the megacity of Istanbul. By combining the various multi-track InSAR datasets (291 images in total) and analysing persistent scatterers (PS-InSAR), we present mean velocity maps of ground surface displacement in selected areas of Istanbul. We identify several sites along the terrestrial and coastal regions of Istanbul that underwent vertical ground subsidence at varying rates, from 5 ± 1.2 mm/yr to 15 ± 2.1 mm/yr. The results reveal that the most distinctive subsidence patterns are associated with both anthropogenic factors and relatively weak lithologies along the Haramirede valley in particular, where the observed subsidence is up to 10 ± 2 mm/yr. We show that subsidence has been occurring along the Ayamama river stream at a rate of up to 10 ± 1.8 mm/yr since 1992, and has also been slowing down over time following the restoration of the river and stream system. We also identify subsidence at a rate of 8 ± 1.2 mm/yr along the coastal region of Istanbul, which we associate with land reclamation, as well as a very localised subsidence at a rate of 15 ± 2.3 mm/yr starting in 2016 around one of the highest skyscrapers of Istanbul, which was built in 2010.