A five-story steel lab-scale structure is analyzed to explore variations of the fundamental period with damage. Five non-null damage states are simulated. Time series, power spectral density and damping are analyzed. Contact-less measurements and urban scenarios are also performed. A 0.38 s period dominates and variations of 5% and 60% were obtained for damage grades D1 and D5. Damping increased with increasing damage. Radar contactless measurements provided consistent results. The period scenario for a district of Barcelona showed soil-building resonant effects.

Accurate estimation of Snow Water Equivalent (SWE) from satellite platforms remains one of the most complex challenges in cryospheric remote sensing, primarily limited by temporal coherence loss over natural surfaces and the complex dielectric interaction of radar signals with heterogeneous snowpacks. While C-band Interferometric Synthetic Aperture Radar (InSAR) has demonstrated theoretical potential for detecting snow accumulation via refractive phase delays, its operational application is often hindered by decorrelation phenomena and the instability of natural targets in alpine environments. Active Reflectors (AR), electronic devices traditionally employed for radiometric calibration and geodetic stability monitoring, have not yet been fully exploited for direct snowpack characterization. This study presents a novel methodological approach based on the installation of a C-band Active Reflector positioned flush with the ground surface, allowing natural snow accumulation directly over the device. The system, designed for operation with the Sentinel-1 constellation, integrates separate receiving and transmitting patch antennas with 42 dB radio frequency amplification, ensuring a stable phase response and dominant backscatter signal. The experimental campaign, conducted in Courmayeur (Italy) during the winter of 2024–2025, validated the system capability to provide point-scale SWE measurements through interferometric phase analysis. The system successfully tracked the evolution of the snowpack, measuring a peak SWE of approximately 250 mm, in close agreement with the in situ measurements. Statistical analysis reveals a high correlation between estimated and ground truth values (R2 > 0.93) for both Sentinel-1 descending relative orbits 066 and 139, with a Root Mean Square Error (RMSE) generally below 26 mm. These results indicate that this technology, by overcoming the logistical limitations of passive reflectors, can provide essential calibration nodes for future SAR missions and for data assimilation in hydrological models.

The availability of displacement maps based on Multi-Temporal Satellite SAR Interferometry (MT-InSAR) has greatly increased, particularly since the launch of the Copernicus Sentinel-1 satellites in 2014. These satellites provide open and free data, leading to services like the European Ground Motion Service (EGMS) which offers highly detailed displacement maps across Europe. Despite their potential for territorial management and risk assessment, the use of these maps is limited due to the complexity of the data and the lack of experience in interpreting MT-InSAR results. Projects such as RASTOOL and SARAI aim to address this by developing automated tools that simplify and expedite the analysis of EGMS data. The ADATools suite, including ADAFinder, ADAClassifier, and ADAImpact, automates the identification, classification, and impact assessment of active deformation areas (ADAs). These tools facilitate the use of displacement data for non-experts, supporting better management of territorial and infrastructural risks. Examples of ADATools applications to EGMS data highlight their strengths and future development potential, as part of the SARAI project.

This work aims to compare and assess the performance of certain methodologies for shoreline mapping based on the use of medium (10 m) and high resolution (3 m) multi-spectral imagery, provided by Sentinel-2 (S2) and PlanetScope (PS), respectively. Being Sentinel-2 part of the Copernicus missions, its data are freely available. PS imagery are also freely available for scientific research, upon approval by the European Space Agency of a related project proposal. Several spectral indices, including Normalized Difference Water Index (NDWI), Modified Normalized Difference Water Index (MNDWI), Automated Water Extraction Index (AWEI), and Water Index (WI), were used for shoreline detection. In particular, two unsupervised classification techniques, the Gaussian Mixture Model (GMM) and K-means clustering were deployed as shoreline extraction methods. The outcomes of such approaches were validated using reference shorelines derived from aerial orthomosaics, generated from images acquired as close as possible to the satellite imagery dates, and the ”baseline and transect” approach for accuracy verification. Three tide-less Mediterranean beaches were used as study cases for comparison: the beach between Castelldefels and Gava in Spain, Feniglia and Marina di Grosseto in Italy. The results demonstrated sub-pixel accuracy in shoreline extraction, with Mean Absolute Distances ranging from 2 m to 5 m for S2 data and 1.5 m to 2 m for PS data. These findings highlight the potential of freely available satellite data for semi-automatic shoreline detection. Results obtained by using the combination of different indices and methodologies show that the best option may change depending on the considered context, hence future investigations should be dedicated to the development of a procedure for automatically determining the context-based (close to) optimal index-classifier combination.

Abstract. Shoreline represents the boundary between land and sea, and its accurate extraction is of utmost importance because of the economic and ecological value of coastal areas. Nowadays, satellite remote sensing is widely used for monitoring the natural environment. Indeed, satellite remote sensing data are cost-effective and periodically available over large areas at a relatively high spatial resolution. Hence, the automatic shoreline extraction from satellite images is a fundamental task for coastal monitoring and management. Shoreline extraction methods are usually applied to satellite remote sensing data. The goal of this study is to compare the performance of different shoreline extraction methods, such as thresholding and more complex classification approaches, such as Random Forest (RF), Minimum Distance (MD), Maximum Likelihood (ML) and K-means, using both optical and radar images. The considered case study area is the shallow basin of the Orbetello Lagoon and one of its ayre called Feniglia. The data supplier is the Copernicus program, which, through the Sentinel-1 and Sentinel-2 missions, provides medium-resolution, open-access products. The accuracy of the obtained results from both methodologies is checked by validating the extracted shoreline using an aerial orthomosaic and, subsequently, a manually extracted shoreline. A preliminary accuracy assessment was performed for image classification, focusing on extracting four classes: water, soil, urban, and forest, using manual segmentation as a reference. In terms of deviation from the reference shoreline, the results obtained through the analysed methodologies achieved an accuracy of 3.75 m, less than half of the pixel size of the Sentinel-1 and Sentinel-2 used products.

This paper reports the design and implementation of a circularly polarized microstrip array antenna operating in C-band. The antenna was designed to upgrade a C-band active reflector to be used with the ESA Sentinel-1 satellite SAR. The use of circular polarization improves the exploitation of the single polarization active reflectors allowing their use for the complete set of linearly polarized radar images available from the SAR acquisitions. This improvement can be done simply by replacing one of its two antennas. High gain, low cost, and a fine axial ratio are the main requirements of this prototype. Results show a good agreement between simulations and measurements, moreover, the close-range operational test done with the active reflector using the proposed antenna demonstrates the feasibility of the idea described in this work.

Abstract. Carrying out monitoring surveys in seismic regions is good practice both for the assessment of land deformation and the evaluation of building structures standing on it. In this work, topographic levelling and DInSAR techniques have been used for displacement measurement. These geomatic techniques are rarely applied in the same context and attempts are made to combine the results obtained for having a complete analysis of the site. The proposed work analyses, compares and discusses topographic levelling and advanced multi-temporal DInSAR techniques used to detect and measure ground deformation when the occurrence of seismic events might have played a role in the displacement. The area of interest had already been under observation through ground-based monitoring surveys, by means of metal bolts attached to façades of buildings detected by topographic level, from 1998 to 2021. The DInSAR analysis was carried out exploiting Sentinel-1A/B data acquired during the period 2014–2021. The goal of the DInSAR processing stage of the procedure is to derive the deformation map of the area of interest from SAR data. A zero date has been set for both survey methods in order to define similar time series for comparison analysis. The results showed that ground displacements measured by levelling and DInSAR have similar trends. On the geomorphological aspect, the same distribution map of terrain subsidence is found in both techniques.

This paper is focused on the design, implementation and testing of an active reflector, to be used to support deformation monitoring studies based on Synthetic Aperture Radar interferometry. The device is designed to work in C-band with Sentinel-1 data, operating at 5.405 GHz ± 50 MHz. A brief description of the active reflector is provided. It consists of two antennas and an amplifying section. The active reflector has been tested in different experiments. In this paper, we describe the experiment carried out in the Parc Mediterrani de la Tecnologia (Castelldefels, Barcelona). The result shows a strong correlation with temperature. A calibration test was carried out to experimentally derive a calibration curve to correct the effect of temperature on phase stability.

This paper is focused on SAR interferometry for deformation monitoring, based on the use of passive and active reflectors. Such reflectors are needed in all cases where a sufficient response from the ground is not available. In particular, the paper describes the development of a low-cost active reflector. This development was carried out in an EU H2020 project called GIMS. The paper summarizes the key characteristics of the developed active reflector. The reflector was tested in two main experiments: the first one located in the campus of CTTC and the second one in a GIMS test site located in Slovenia. The experiments demonstrate the visibility of the active reflectors and provide the first results concerning the phase stability of such devices.

This paper describes the application of spaceborne and Ground Based radar interferometry as a tool for assisting the management of emergencies related to land movements. The support of the two techniques is carried out integrating some products, using tools available from a software and hardware architecture specifically developed within HEIMDALL, a H2020 project, devoted to providing a multi-hazard Cooperative Management, for Data Exchange, Response Planning and Scenario Building. Deformation maps obtained processing Sentinel-1 SAR images, updated every six days, can provide information over a large area, to be used during the preparedness and recovery phases. Data acquired through a Ground Based SAR system installed in-situ, provide a continuous and discontinuous (periodical) monitoring, aiming at supporting response and recovery phases. The products, in both cases, consist of deformation maps and temporal series, velocity of displacement, obtained through the application of Persistent Scatterer Interferometry (PSI).

A Ku band-terrestrial radar interferometer with different polarization combination capability, including left and right circular polarization (CP), has been used to investigate the potential of different co-polar and cross-polar acquisitions for Terrestrial Radar interferometry (TRI), aiming at improving the monitoring of landslides in semi-urban areas. After some preliminary tests carried out to verify the responses of simple targets, Ground Based SAR images acquired in a test area affected by a landslide have been analyzed. The study of how different polarization combinations affect coherence and amplitude dispersion of natural media and man-made structures has been carried out to evaluate the potentialities of the different polarization observations, aiming at easing the identification of stable scatters.

The use of Sentinel-1 SAR images for snow behavior monitoring and its parameters estimation is one of the most studied applications, but due to the high temporal and spatial heterogeneity of this media, is quite challenging. The presence of reference targets in the observed areas is of main concern both for amplitude and interferometric based techniques, but in a typical scenario as snow covered slopes or glaciers there is a lack of stable natural targets; this can demand the installation of Corner Reflectors. In this study, the design and the first test of an active corner reflector (ACR) operating at 5.405 GHz ± 50 MHz band, designed to be used in support to ESA Sentinel-1 spaceborne SAR images analysis and processing, is reported. The system here described was designed aiming at a tradeoff among low cost, simple functioning, easy and rugged hardware, to be deployed also in sites, as snow covered areas and glaciers. Using off-the-shelf components, one of the most challenging issue is to obtain a device with an adequate phase stability over long temporal interval.

This paper reports the design and preliminary test of a circular polarized patch array antenna operating in C band. The antenna was designed as part of a C band Active Corner reflector (ACR). The operating band is 5.405 GHz ± 50 MHz band, the same used by ESA Sentinel-1 SAR. The main requirements for the antenna system are: a simple design to assure an adequate phase stability, simple installation, and low cost, as requested for the proposed ACR.

This work presents an assessment on the correlation between CyGNSS-derived Global Navigation Satellite Systems Reflectometry (GNSS-R) bistatic reflectivity l  and SMAP-derived brightness temperature B T , over land surfaces. This parametric-study is performed as a function of Soil Moisture Content (SMC), vegetation opacity τ, and albedo ω. Several target areas are selected to evaluate potential differentiated geophysical effects on “active” (as many transmitters as navigation satellites are in view), and passive approaches. Although microwave radiometry has potentially a better sensitivity to SMC, the spatial resolution is poor ~ 40 km. On the other hand, GNSS-R bistatic coherent radar footprint is limited by half of the first Fresnel zone which provides about ~ 150 m of spatial resolution (depending on the geometry). The synergetic combination of both techniques could provide advantages with respect to active monostatic Synthetic Aperture Radar (SAR).

An experimental assessment of the performance of Global Navigation Satellite Systems Reflectometry (GNSS-R) for biomass monitoring over tropical forests is presented. Several observables of the so-called Delay Doppler Maps (DDMs), as provided by the Cyclone Global Navigation Satellite Systems (CyGNSS) microsatellites constellation, are evaluated using the pan-tropical Above Ground Biomass (AGB) map provided by Avitabile et al. and Canopy Height (CH) data derived from the Geoscience Laser Altimeter System (GLAS) lidar-instrument on-board the National Aeronautics and Space Administration NASA’s Ice, Cloud, and land Elevation Satellite (ICESat). In so doing, different tropical forests types are studied. Preliminary results show that the spreading of the DDMs in the delay domain has a sensitivity up to a mean AGB ~ 325 ton/ha over Congo rainforests for elevation angles in the range e  ~ [20, 40] º.

This paper reports the results of two terrestrial surveys aimed at monitoring two Alpine glaciers located in Italy and Spain respectively, and carried out using a Ground Based SAR interferometer. Although the monitoring of glaciers based on this technique does not represent a novelty, these two case studies are peculiar, due to the characteristics of the Alpine glaciers among which the dominant role of the atmospheric phase screen (APS) on the radar signal propagation. These kind of glaciers, with their climate and geographical features, often demand a detailed analysis of the acquired data, at small temporal (less than an hour), and spatial (a few square meters) scale. The meteorological conditions, which affect the dynamics of the glaciers, deeply influenced the backscattering behavior, demanding a careful analysis of the amplitude of the radar signal, to characterize the surface, and of the interferometric phase, to evaluate the role of the APS. Only after the correction of the APS, a final accuracy of a few millimeters/day was attained in the daily velocity of the glacier in both cases.

anthropic World Heritage Sites are threatened by of placed on geohazards appears to be poor, if compared with the others potential threatening factors, such as uncontrolled urban development of This study, therefore, shows a new satellite data analysis procedure to identify, in a fast, simple and repeatable way, the temporal and spatial evolution of the most critical and reliable ground deformation areas related to slow-kinematic geohazards (volcanic activity, slow-moving landslides or ground-subsidence). This approach has been tested in the Tuscan UNESCO sites (Central Italy). Thanks to the main characteristics of the recent Sentinel-1 data (short revisit time, systematic and free availability for all data users and worldwide coverage), this procedure can be easily exploited by the local risk management decision makers of each World Heritage Site, in order to define long-term geohazards monitoring activities and conservation strategies.

ABSTRACT This work combines very detailed measurements from terrestrial laser scanner (TLS), ground-based interferometry radar (GB-SAR) and ground-penetrating radar (GPR) to diagnose current conditions and to analyse the recent evolution of the Monte Perdido Glacier in the Spanish Pyrenees from 2011 to 2017. Thus, this is currently one of the best monitored small glacier (<0.5 km 2 ) worldwide. The evolution of the glacier surface was surveyed with a TLS evidencing an important decline of 6.1 ± 0.3 m on average, with ice losses mainly concentrated over 3 years (2012, 2015 and 2017). Ice loss is unevenly distributed throughout the study period, with 10–15 m thinning in some areas while unchanged areas in others. GB-SAR revealed that areas with higher ice losses are those that are currently with no or very low ice motion. In contrast, sectors located beneath the areas with less ice loss are those that still exhibit noticeable ice movement (average 2–4.5 cm d ─1 in summer, and annual movement of 9.98 ma ─1 from ablation stakes data). GPR informed that ice thickness was generally <30 m, though locally 30–50 m. Glacier thinning is still accelerating and will lead to extinction of the glacier over the next 50 years.