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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 50 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 (LS) 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: (i) Land subsidence rate has been more variable in space but less variable over time than the changes of the NA mean sea level; o average subsidence has amounted to 0.8 mm/yr and the average NA msl rise to 1.9 mm/yr; (ii) minimum and maximum cumulative subsidence has totalled 8 mm and 93 mm, respectively; (iii) 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.

We use satellite observations to document rapid acceleration and ice loss from a formerly slow-flowing, marine-based sector of Austfonna, the largest ice cap in the Eurasian Arctic. During the past two decades, the sector ice discharge has increased 45-fold, the velocity regime has switched from predominantly slow (~ 101 m/yr) to fast (~ 103 m/yr) flow, and rates of ice thinning have exceeded 25 m/yr. At the time of widespread dynamic activation, parts of the terminus may have been near floatation. Subsequently, the imbalance has propagated 50 km inland to within 8 km of the ice cap summit. Our observations demonstrate the ability of slow-flowing ice to mobilize and quickly transmit the dynamic imbalance inland; a process that we show has initiated rapid ice loss to the ocean and redistribution of ice mass to locations more susceptible to melt, yet which remains poorly understood. Key Points Recent dynamic activation of a formerly slow-flowing marine Arctic ice capImbalance has spread 50 km inland to within 8 km of the ice cap summitIce discharge has increased 45-fold, and thinning rates have exceeded 25 m/yr

Ice velocity is an important parameter to evaluate the dynamic response of glaciers to climate change. Repeat pass SAR data enable the measuring of ice motion with high accuracy through differential processing techniques, including SAR interferometry and offset tracking. In order to validate and inter-compare ice velocity maps generated by various techniques at different institutions, Round Robin Exercises were initiated in the frame of the ESA Glacier Climate Change Initiative (CCI) project. Standardised datasets (SAR and optical repeat pass satellite scenes) were prepared for three different test sites. The participants were invited to select a data set, apply their software/technique of choice for ice flow mapping, and return the results together with a feedback form describing the processing steps and selected parameters in detail. Here we summarise the results of the comparisons only for the SAR data sets over three test sites.

With a surface area of about 550 km2 the Venice Lagoon is the largest Italian wetland, open in the Upper Adriatic Sea to the highest tides of the Mediterranean Sea. The lagoon is connected to the sea through three inlets, which divide the narrow littoral strip separating the inner water body from the Adriatic. Several nearshore and offshore structures have been constructed over the decades to protect such a unique city and its coastal environment from sea storms and high waters, whose frequency and level are increasing due to relative sea level rise. Long jetties have been built at the inlets between the end of the 18th and beginning of the 19th centuries and then reinforced between 1994 and 1997. Since 2003, in the framework of the MOSE construction (i.e., the project of mobile barriers for the temporarily closure of the lagoon to the sea), the jetties have been extended, new breakwaters have been constructed in front of the inlets, and a small island has been realized within the Lido inlet to support the MOSE gates. An accurate quantification of the movements of these coastal defense structures due to long-term consolidation has been carried out by Persistent Scatterer Interferometry (PSI) using ENVISAT ASAR and TerraSAR-X images acquired from April 2003 to December 2009 and from March 2008 to January 2009, respectively. The displacements range between few mm/yr for the structures older than 10 years up to 50-70 mm/yr for those realized few years ago. The PSI measurements have been combined with the outcome of a detailed geomechanical characterization of the lagoon subsoil down to -50 m depth below msl. The geotechnical dataset has been collected at a test site located on the northern littoral where an instrumented 20 m radius, 6.7 m high vertically-walled reinforced sand embankment was built at the end of 2002 and monitored till to 2007. The use of the derived stress-strain properties together with the actual lithostratigraphy below the structures, which is available from several piezocone profiles and boreholes, allow for the computation of secondary compression (consolidation) rates that match very well the PSI-derived movements. The results provide important information on the expected time-dependent settlement of these structures and prove the potentiality of PSI in controlling the geomechanical response of large coastal structures.

directly measured with remotely sensed data. However, many parameters which influence the ground thermal regime and surface indicators can be captured with satellite data in an operational manner. Those are e.g. land surface temperature, land cover and snow parameters, soil moisture and terrain changes. Within the ESA DUE Permafrost project a wide range of EO datasets are investigated and integrated in an information system with extensive involvement of the permafrost research community. This comprises pan-boreal/arctic to regional and local scale investigations. The capabilities of currently available remotely sensed datasets have been assessed with respect to operational monitoring. This paper summarizes those components of the processing system which address automatized integration of remotely sensed products: land surface temperature, soil moisture (incl. freeze/thaw), open water, snow parameters and methane.1

Le livellazioni geometriche sono state nel secolo scorso l'unico metodo di rilievo altimetrico che abbia consentito di misurare con precisione l'entità della subsidenza "moderna" dell'area costiera nord adriatica. Solo alla fine degli anni 1990 è stata istallata una rete per misure GPS in differenziale (DGPS) e in continuo (CGPS). Nell'ultimo decennio inoltre, l'utilizzo del radar ad apertura sintetica (SAR) su vettori satellitari ha consentito lo sviluppo e l'affinamento dell'analisi interferometrica differenziale (InSAR) e dell'analisi interferometrica su riflettori persistenti (IPTA) che si sono dimostrati di estrema efficacia per lo studio dei movimenti verticali del suolo. Nel caso della pianura costiera Veneta, sono stati utilizzati i satelliti ERS-1/2 ed ENVISAT dell'Agenzia Spaziale Europea, rispettivamente per il periodo 1992-2005 e 2003-2009, ed il satellite TerraSAR-X dell'Agenzia Spaziale Tedesca, per il biennio 2008-2009. Oggi si dispone di una densità di dati SAR che, data la risoluzione spaziale dei satelliti tra 20 e 3 m, è maggiore di circa 2 ordini di grandezza nelle l'analisi a scala regionale e più di 3 ordini per analisi locali rispetto alle misure tradizionali su capisaldi. Ciò ha permesso la mappatura dei movimenti del suolo a scala "regionale" (100×100 km2), locale (10×10 km2) e puntale al livello di singole strutture. Le serie di dati SAR sono stati calibrati e validati con le misure altimetriche di livellazione, DGPS e CGPS nella rete di monitoraggio ISES-IRMA. Grazie all'elevata densità di informazioni, all'ottima risoluzione spaziale e accuratezza verticale millimetrica del monitoraggio SAR è emersa una dinamica verticali del territorio costiero Veneto diversa da quanto ottenibile utilizzando le sole tecniche di livellazione tradizionale. L'immagine attuale indica che il processo subsidenziale si esplica con una forte variabilità spaziale, sia a scala regionale che locale. L'analisi integrata dei dati altimetrici e delle numerose nuove informazioni sul sottosuolo, recentemente acquisite nell'ambito di una serie di ricerche condotte dagli Autori, ha permesso la caratterizzazione delle componenti dei movimenti verticali del suolo della pianura costiera Veneta in funzione della profondità alla quale agiscono e la loro distribuzione areale.

Anthropogenic land subsidence has widely been affecting the Veneto Region; northern Italy; since the past century. Groundwater withdrawals for industrial; domestic; and agricultural uses; exploitation of mineral water; thermal water for health treatment; methane-bearing water; and peat oxidation in reclaimed farmlands produced a land settlement varying in time and space throughout the area. Moreover; natural consolidation of the Quaternary deposits and tectonics of the pre-Quaternary basement contribute to increase ground surface lowering. Different survey techniques; with different characteristics; have been adopted to control land subsidence. To overcome the limits that characterize each single method and to enlarge the knowledge on regional land subsidence; an integrated monitoring method has been designed to accurately and reliably keep land movements under control in the study area. We combine five earth observation techniques; i.e. spirit leveling; Continuous Global Positioning System (CGPS); Differential GPS (DGPS); Interferometric Synthetic Aperture Radar (InSAR); and Interferometric Point Target Analysis (IPTA); together over about the last ten-years; and homogenized and integrated their results in both the time and space domains. The application of this Subsidence Integrated Monitoring System (SIMS) provides a new complete and dependable picture of the vertical displacements in the Veneto Region never available before

Our knowledge of the dynamics of vertical ground movements plays a fundamental role in the study of the geomorphological processes, particularly for determining sediment deposition and erosion causes. The conservation of lagoon morphological structures such as salt marshes and tidal flats, besides erosion due to waves and currents, depends on their surface height with respect to the sea level that, for short periods, is primarily related to the land subsidence process and secondarily to eustasy. Ground vertical variations with respect to the sea level, even if small, can, in fact, trigger sediment erosion and deposition processes. To determine land displacement rates in small islands of the Venice Lagoon not covered by traditional surveys (levelling and differential GPS), SAR-based monitoring techniques, i.e. differential SAR interferometry (INSAR) and interferometric point target analysis (IPTA) from ERS-1 and ERS-2 satellites, were performed. We will use the Murano Island for our example in this contribution.