Ers and Envisat Differential Sar Interferometry for subsidence monitoring

This paper reports on the potential of differential SAR interferometry to map land subsidence. After a presentation of the methodology, the focus will be on feasibility demonstration and accuracy assessment. The theoretical considerations are verified with the selected cases Ruhrgebiet, Mexico City, Bologna, and Euganean Geothermal Basin, representing fast (m/year) to slow (mm/year) deformation velocities. The accuracy of the generated deformation maps and the maturity of the required processing techniques lead to the conclusion that differential SAR interferometry has a very high potential for operational mapping of land subsidence. The high reliability of the ERS satellites, with the huge data archive starting in 1991, strongly supports this application. The planned ENVISAT ASAR has the potential to maintain good data availability into the future. This will, nevertheless, strongly depend on the sensor operation strategy

Landslide mapping in Switzerland with ENVISAT ASAR

In the frame of the IGARSS 2012 special session on ENVISAT the landslide mapping activities in Switzerland using ENVISAT ASAR data are presented. Between 2005 and 2010 the building up of a well suited archive over the Swiss Alps was realized through programming of all IS2 mode data during the snow free period. In recent years DINSAR and PSI based landslide inventory and monitoring products started to play an important role in the updating of hazard maps

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Computing the relative land subsidence at Venice, Italy, over the last fifty years

Abstract: Land subsidence causes various damages to the infrastructures and cultural heritage in many cities worldwide. Urban flooding is one of the main consequences of land subsidence in coastal cities, where it is exacerbated by sea-level rise accompanying global climate change, but also in inland metropolitan areas such as Mexico City, where subsidence zones are increasingly flooded following intense rainstorms. The subsidence of Venice, one of the most beautiful and famous cities in the world, is well known not for the magnitude of subsidence but because subsidence has seriously compromised the heritage and the safety of the city in relation to its small elevation above the sea. The storm that flooded the historical center of Venice on November 4, 1966 dramatically revealed its fragility with respect to land subsidence and sea-level rise, or the Relative Land Subsidence (RLS), i.e. land movement with respect to sea-level changes. That event signaled the beginning of a systematic monitoring of the loss in elevation of the ground surface of Venice with respect to the mean level of the Northern Adriatic (NA) Sea. Tide gauge measurements, available from the beginning of the last century, have been supplied historically by levelling and more recently by Synthetic Aperture Radar (SAR)-based Interferometry. On the occasion of the 50th anniversary of the 1966 flood event, we quantify the RLS experienced by the city over these last five decades with a detail never achieved before. The computation of the loss of elevation has been obtained by processing and superposing the results of levelling surveys carried out in 1961, 1969, 1973, and 1993, together with the results of Interferometric processing of SAR images acquired from satellites: 1993 to 2002 by ERS-1/2, 2003 and 2010 by ENVISAT, 2008 to 2013 by TerraSAR-X, and 2012 to 2016 by COSMO-SkyMED. The records from the tide gauge in Trieste, which is a city on the coast of the NA Sea close to the Alps and known to be stable, are used to evaluate the sea-level rise over the targeted time interval. The mean land velocity (v) for each analyzed period has been obtained by interpolating the original measurements using the Kriging method on a same regular 50-m grid covering the entire city. Then, cumulative land subsidence (LStot)) from 1966 to 2016 has been simulated in a GIS environment by summing the partial land subsidence over the various periods covered by the levelling and SAR surveys. The results point out that in the Venice historical center between 1966 and 2016: • Land subsidence rate has been more variable in space but less variable over time than the changes of the NA mean sea level; • average subsidence has amounted to 0.8 mm/yr and the average NA msl rise to 1.9 mm/yr; • minimum and maximum cumulative subsidence has totalled 8 mm and 93 mm, respectively; and • maximum loss of elevation with respect to the NA msl (i.e. RLS) has been 190 mm. RLS has produced a tangible effect on the Venice historical center revealed by the continuous increase in frequency of the flooding events, locally called "acqua alta". In the next years, any further loss of elevation with respect to the mean sea level, even a few mm, will threaten the city’s survival with severe social and environmental impacts. Considering the present average land subsidence of Venice and sea level rise of the NA (i.e. both about 1.2 mm/yr), an additional loss of elevation of about 190 mm will likely occur by 2100. Actually, according to conservative and pessimistic IPCC scenarios, the sea-level accompanying global climate change is expected to rise from 32 to 56 cm. Therefore, the outcomes from this study should be properly taken in account for the planning of effective interventions for the mitigation of climate changes to maintain the historical center of this unique city

COSMO-SkyMed vs RADARSAT-2 for Monitoring Natural and Anthropogenic Components of the Land Movements in Venice

We present the result of a test aimed at evaluating the capability of RADARSAT-2 and COSMO-SkyMed to map the natural subsidence and ground movements induced by anthropogenic activities in the historical center of Venice. Firstly, ground movements have been retrieved at quite long- and short-term by the Persistent Scattered Interferometry (PSI) on 2008-2015 RADARSAT-2 and 2013-2015 COSMO-SkyMed image stacks, respectively. Secondly, PSI has been calibrated at regional scale using the records of permanent GPS stations. Thirdly, considering that over the last two decades “in the historical center of Venice” natural land movements are primarily ascribed to long-term processes, and those induced by human activities act at short-term, we have properly resampled 83-month RADARSAT-2 C-band and 27-month COSMO-SkyMed X-band interferometric products by a common grid and processed the outcome to estimate the two components of the displacements. Results show that the average natural subsidence is generally in the range of 0.9 – 1.1 mm/yr and the anthropogenic ground movements are up to 2 mm/yr

Computing the relative land subsidence at Venice, Italy, over the last fifty years

Abstract: Land subsidence causes various damages to the infrastructures and cultural heritage in many cities worldwide. Urban flooding is one of the main consequences of land subsidence in coastal cities, where it is exacerbated by sea-level rise accompanying global climate change, but also in inland metropolitan areas such as Mexico City, where subsidence zones are increasingly flooded following intense rainstorms. The subsidence of Venice, one of the most beautiful and famous cities in the world, is well known not for the magnitude of subsidence but because subsidence has seriously compromised the heritage and the safety of the city in relation to its small elevation above the sea. The storm that flooded the historical center of Venice on November 4, 1966 dramatically revealed its fragility with respect to land subsidence and sea-level rise, or the Relative Land Subsidence (RLS), i.e. land movement with respect to sea-level changes. That event signaled the beginning of a systematic monitoring of the loss in elevation of the ground surface of Venice with respect to the mean level of the Northern Adriatic (NA) Sea. Tide gauge measurements, available from the beginning of the last century, have been supplied historically by levelling and more recently by Synthetic Aperture Radar (SAR)-based Interferometry. On the occasion of the 50th anniversary of the 1966 flood event, we quantify the RLS experienced by the city over these last five decades with a detail never achieved before. The computation of the loss of elevation has been obtained by processing and superposing the results of levelling surveys carried out in 1961, 1969, 1973, and 1993, together with the results of Interferometric processing of SAR images acquired from satellites: 1993 to 2002 by ERS-1/2, 2003 and 2010 by ENVISAT, 2008 to 2013 by TerraSAR-X, and 2012 to 2016 by COSMO-SkyMED. The records from the tide gauge in Trieste, which is a city on the coast of the NA Sea close to the Alps and known to be stable, are used to evaluate the sea-level rise over the targeted time interval. The mean land velocity (v) for each analyzed period has been obtained by interpolating the original measurements using the Kriging method on a same regular 50-m grid covering the entire city. Then, cumulative land subsidence (LStot)) from 1966 to 2016 has been simulated in a GIS environment by summing the partial land subsidence over the various periods covered by the levelling and SAR surveys. The results point out that in the Venice historical center between 1966 and 2016: • Land subsidence rate has been more variable in space but less variable over time than the changes of the NA mean sea level; • average subsidence has amounted to 0.8 mm/yr and the average NA msl rise to 1.9 mm/yr; • minimum and maximum cumulative subsidence has totalled 8 mm and 93 mm, respectively; and • maximum loss of elevation with respect to the NA msl (i.e. RLS) has been 190 mm. RLS has produced a tangible effect on the Venice historical center revealed by the continuous increase in frequency of the flooding events, locally called "acqua alta". In the next years, any further loss of elevation with respect to the mean sea level, even a few mm, will threaten the city’s survival with severe social and environmental impacts. Considering the present average land subsidence of Venice and sea level rise of the NA (i.e. both about 1.2 mm/yr), an additional loss of elevation of about 190 mm will likely occur by 2100. Actually, according to conservative and pessimistic IPCC scenarios, the sea-level accompanying global climate change is expected to rise from 32 to 56 cm. Therefore, the outcomes from this study should be properly taken in account for the planning of effective interventions for the mitigation of climate changes to maintain the historical center of this unique city

Land subsidence in coastal environments: Knowledge advance in the Venice coastland by TerraSAR-X PSI

The use of satellite SAR interferometric methods has significantly improved the monitoring of ground movements over the last decades, thus opening new possibilities for a more accurate interpretation of land subsidence and its driving mechanisms. TerraSAR-X has been extensively used to study land subsidence in the Venice Lagoon, Italy, with the aim of quantifying the natural and anthropogenic causes. In this paper, we review and update the main results achieved by three research projects supported by DLR AOs (German Aerospace Center Announcement of Opportunity) and conducted to test the capability of TerraSAR-X PSI (Persistent Scatterer Interferometry) to detect ground movements in the complex physiographic setting of the Venice transitional coastal environment. The investigations have been focused on the historical center of Venice, the lagoon inlets where the MoSE is under construction, salt marshes, and newly built-up areas in the littoral. PSI on stacks of stripmap TerraSAR-X images covering short- to long-time periods (i.e., the years 2008\u20132009, 2008\u20132011 and 2008\u20132013) has proven particularly effective to measure land subsidence in the Venice coastland. The very high spatial resolution (3 m) and the short repeat time interval (11 days) of the TerraSAR-X acquisitions make it possible to investigate ground movements with a detail unavailable in the past. The interferometric products, properly calibrated, allowed for a millimetric vertical accuracy of the land movements at both the regional and local scales, even for short-term analyses, i.e., spanning one year only. The new picture of the land movement resulted from processing TerraSAR-X images has significantly contributed to update the knowledge on the subsidence process at the Venice coast

Combining L- and X-Band SAR interferometry to assess ground displacements in heterogeneous coastal environments: The Po River Delta and Venice Lagoon, Italy

From leveling to SAR-based interferometry, the monitoring of land subsidence in coastal transitional environments significantly improved. However, the simultaneous assessment of the ground movements in these peculiar environments is still challenging. This is due to the presence of relatively small built-up zones and infrastructures, e.g., coastal infrastructures, bridges, and river embankments, within large natural or rural lands, e.g., river deltas, lagoons, and farmland. In this paper we present a multi-band SAR methodology to integrate COSMO-SkyMed and ALOS-PALSAR images. The method consists of a proper combination of the very high-resolution X-band Persistent Scatterer Interferometry (PSI), which achieves high-density and precise measurements on single structures and constructed areas, with L-band Short-Baseline SAR Interferometry (SBAS), properly implemented to raise its effectiveness in retrieving information in vegetated and wet zones. The combined methodology is applied on the Po River Delta and Venice coastland, Northern Italy, using 16 ALOS-PALSAR and 31 COSMO-SkyMed images covering the period between 2007 and 2011. After a proper calibration of the single PSI and SBAS solution using available GPS records, the datasets have been combined at both the regional and local scales. The measured displacements range from ~0 mm/yr down to -35 mm/yr. The results reveal the variable pattern of the subsidence characterizing the more natural and rural environments without losing the accuracy in quantifying the sinking of urban areas and infrastructures. Moreover, they allow improving the interpretation of the natural and anthropogenic processes responsible for the ongoing subsidence