On November 10, 2023, the town of Grindavik on the Reykjanes peninsula (Iceland) was evacuated due to the propagation of a shallow magmatic fissure near the town. We programmed Pléiades images on the area via the CIEST2initiative. Due to the vicinity of the affected area to the ocean, the lava flow might reach the water modifying submarine topography. Our goal is to test a new space-based method to measure shallow bathymetry and possible submarine lava flow volume in shallow water. Our method is based on the time lag that exists within a single Pleiades dataset (i.e. the panchromatic and multispectral images). We use this time lag to measure wave motion, their celerity and their period (c,T). Then, we solve the linear dispersion relation as a function of waves period, for each (c,T) pairs independently, to find water depth. This method has high potential for shallow submarine morphology mapping.

Following the 7.8 magnitude earthquake that struck Turkey and Syria on February 6, 2023, TomoSAR, an extensive software designed for SAR image processing, demonstrated its effectiveness in assessing land subsidence. It provided the initial three-dimensional displacement data, marking a significant milestone in this field. Notably, TomoSAR stands out as the first publicly accessible tool capable of jointly processing Persistent and Distributed Scatterers (https://github.com/DinhHoTongMinh/TomoSAR). Continual efforts are underway to elevate TomoSAR’s accessibility and performance. This involves integrating algorithms into a parallel version to facilitate enhanced performance and open avenues for complimentary scientific services at no cost.

In this study, we investigated the ability of deriving cyclic/annual motion information from Persistent Scatterers Interferometric (PSI) Time Series. One of the potential applications of such information is to characterize and map motion related to clay Swelling/Shrinking phenomena. Such an application could become particularly interesting with the development of nation/continent wide service based on PSI (such as EGMS from Copernicus). We identified biases affecting the PSI data limiting the approach that must be investigated in further works.

We present an analysis of coastal subsidence in Europe based on the recent European Ground Motion Service (EGMS) product. First, we compare EGMS products with vertical land velocities from the permanent Global Navigation Satellite System (GNSS) network. Overall, we find a reasonable agreement with a correlation coefficient of 0.94 between the vertical velocities estimates from GNSS stations and the collocated EGMS pixels. However, we obtain systematically more negative values (of up to 1 mm/yr) from EGMS estimates. These deviations could be related to the different reference frame used to calibrate EGMS (ETRF2000) and GNSS (IGS2014). Second, we combine coastal flood plain defined from the new Copernicus digital elevation model (25m resolution) and the EGMS estimates to identify subsiding coastal flood plains at the scale of Europe.

The European Ground Motion Service (EGMS) is part of the Copernicus Land Monitoring Service (CLMS) managed by the EEA (European Environment Agency) [1]. EGMS is based on the full resolution InSAR processing of ESA Sentinel-1 (S1) acquisitions over Europe (Copernicus Participating states) [2]. The first release or baseline includes ground motion time-series between 2015 and 2020. This open data service has yearly updates.The EGMS employs persistent scatterer (PS) and distributed scatterer (DS) in combination with a Global Navigation Satellite System (GNSS) model to calibrate the ground motion products. This public dataset consists of three products levels (L2a/Basic, L2b/Calibrated and L3/Ortho). The Basic and Calibrated product levels are full resolution (20x5m) Line of sight (Los) velocity maps from ascending/descending orbits. The Ortho product offers horizontal (East-West) and vertical (Up-Down) anchored to the reference geodetic model resampled at 100x100m.The objective of this paper is to describe the independent validation of this continental scale ground motion time-series dataset. The goal is to ensure that the EGMS products are consistent with user requirements and product specifications and they cover the expected range of applications. To evaluate the fitness of the EGMS ground motion data service 7 reproducible validation activities (VA) have been developed gathering validation data from 50 sites across 12 European countries. Last but not least, a software environment has been developed to carry out all the validation activities and describe/store the data coming from the validation sites.

This paper presents a hydrologically modulated transient motion of world's largest active landslide occurring along the western shore of the Kara-Bogaz-Gol (KBG) lagoon of the Caspian Sea (CS) using Interferometric Synthetic Aperture Radar (InSAR) data. Here a dataset of Sentinel 1A/B IW SAR imagery acquired on ascending and descending modes between 2014 and 2020 has been processed to analyze the present-day evolution of this giant coastal landslide. The results shows that the eastern bank of the KBG lagoon (25x5 km) is horizontally sliding toward the lake at a rate of 25 mm/yr. The time series analysis reveals week-long accelerating slip events when the KBG reservoir water level reached its seasonal maximum. This study presents new information on the potential roles of the hydrological forces modulated by sea-level rises on the ancient landslides which originated during successive CS transgressions in the Late Glacial.

This paper presents the dynamics of the world's largest lateral mega-spreading landslide cluster along the western shoreline of the Aral Sea in Uzbekistan (Central Asia) using Interferometric Synthetic Aperture Radar (InSAR) time series analysis of three Sentinel-1 IW datasets over the period 2015–2020. It extends >50km wide and corresponds to a gravity-induced lateral spreading movement of relatively intact Sarmatian limestone blocks that are sliding over a highly plastic clay layer at rates up to 40 mm/yr with a clear dominance of horizontal motion at a nearly constant velocity. Slow vertical motions (up to 5 mm/yr) are localized along narrow strips of terraces where rock spread is attributed to rotational subsidence.

The systematic availability of data from the Copernicus Sentinel-1 mission, allows redundancy of pairs considered during interferometric processing. In the present work the effect of DInSAR pairs' selection on the interferometric estimates, especially for the case of relatively fast moving landslides, is investigated. Interferometric findings over a well-monitored site are validated by in-situ geodetic measurements. It was documented that significant underestimation of motion occurs for DInSAR solutions utilizing pairs covering larger temporal spans, while displacement patterns are generally maintained. The above fact is attributed mainly to the magnitude of cumulated motion at temporally long interferograms, exceeding the physical limit of SAR interferometric techniques, with pronounced underestimation issues introduced. The need for an a priori knowledge of the expected motion rates for the optimum selection of interferometric combinations for measuring ground displacements is underlined.

This paper presents a method for deriving shallow to intermediate (1m to 50m) coastal bathymetry from space-borne multispectral data taking advantage of the short time-lag between sensors' bands. The idea is to quantify local waves' characteristics (wavelengths and celerities) that are related to the water depths using optical data: local spectral analysis can provide the significant wavelengths and inter-band offset-tracking and the corresponding celerities (knowing the inter-band time-lag). Such an approach was firstly described in [1]. However, for an application to extended areas and using large data sets (as possible with the Sentinel-2 archive), a faster technique is required: the ability of processing large areas and data acquired at different dates is required for actual operational uses. The approach we propose here is based on Fast Fourier Transform analysis in order to simultaneously extract the wavelengths and celerities.

An essential step in earthquake risk assessment consists in collecting information regarding buildings at risks in order to evaluate their vulnerability, and, ultimately, their expected damages for events of specific intensity. A number of building features can be retrieved by means of remote sensing, either directly (through direct observations of features such as their size or footprints) or indirectly (by appraising the expected building types, given features such as the shape of roads or roofs, and an a-priori knowledge of the urban landscape of interest). Here, we evaluate to which extent the accuracy of mean damage grade can be improved by means of remote sensing using the RISK-EU (2004) [1] assessment grid. The results show that if nothing is known regarding the building stocks in the city of interest, the uncertainty in average vulnerability can be reduced by half using remote sensing observations if adequate indirect proxies can be found.

In the presented study our purpose is to show the interest of space-borne high-resolution L-band Synthetic Aperture Radar (SAR) images (ALOS-2/PALSAR2 data in SM1 mode) for mapping deformation of slow landslides. The methods we combined are sub-pixel correlation offset tracking techniques and differential SAR interferometry. Hell-bourg and Grand Ilet landslides (our test cases) are located on La Réunion Island in the Indian Ocean with motions up to about 1 m/y. The produced deformation maps resulted better than those obtained in previous studies with C or X band SAR data or with current Sentinel-1 data as L-band data are less affected by the vegetated cover than X- or C-band data. Finally, the possibility of deriving 3D mapping of the displacement by combining ascending and descending acquisitions (each one provides 2 components of the deformation: line of sight and azimuth) is investigated.

In this paper we present a method to restitute the volcanic gas/ash Plume Elevation Model (PEM) from optical satellite imagery. As the volcanic plume is moving rapidly, conventional satellite based photogrammetric height restitution methods do not apply as the epipolar offset due to plume motion adds up to the one generated by the stereoscopic view. This is because there are time-lags of tens of seconds between conventional satellite stereoscopic acquisitions, depending on the stereo acquisition mode. Our method is based on a single satellite pass. We exploit the short time lag and resulting baseline that exist between the multispectral (MS) and the panchromatic (PAN) bands to jointly measure the epipolar offsets and the perpendicular to the epipolar (P2E) offsets. The first are proportional to plume height plus the offsets due to plume velocity in the epipolar direction. The second, are proportional to plume velocity in the P2E direction only. The latter is used to compensate the effect of plume velocity in the stereoscopic offsets by projecting it on the epipolar direction assuming a known plume direction, thus improving the height measurement precision. We apply the method to Landsat 8 data taking into account the specificities of the focal plane modules. We focus on the Holuhraun 2014 fissure eruption (Iceland). We validate our measurements against ground based measurements. The method has potential for detailed high resolution routine measurements of volcanic plume height/velocity. The method can be applied both to other multi focal plane modules push broom sensors (such as the ESA Sentinel 2) and potentially to other push-broom systems such as the CNES SPOT family and Pléiades.

Before the satellite altimetry era, tide gauges are the unique source of information to monitor global sea level rise due to anthropogenic climate change. As sea level changes display regional variability, its global mean can be estimated by averaging trends from good quality tide gauge. This leads to sea level rise rates of 1.65 +/− 0.2 mm/yr during the 20th century. However, this value and the related uncertainties are subject to discussion: 1. the network of available tide gauges is distributed in an uneven way: most of datasets available cover the Northern hemisphere, whereas previous studies suggest that sea level rise has been different in the northern and southern hemispheres. 2. over the altimetry era (1992-present), the sea level budget can be estimated by summing each contributing factor (mountain glaciers, ice sheets, thermosteric effects, land water storage), within uncertainties reaching 10 to 15% for each component. The same validation is more difficult for the recent period, because less data are available, thus questioning again the precise rate of mean sea level over the 20th century.

Knowing bathymetry at intermediate depth, over large areas, and at a reasonable cost is a key issue. Spaceborne remote sensing techniques must play an essential role in retrieving such bathymetry. In this paper, a method is proposed that aims to address this issue without any in situ measurements by exploiting the characteristics of the SPOT-5 satellite dataset. The proposed method is designed to provide bathymetry from two optical SPOT-5 satellite images separated by a time lag DT of 2.04 s. It relies on the estimation of several clouds of wave celerity and wavelength pairs using wavelet and cross-correlation techniques and on the linear wave dispersion relation. This method has been applied to two SPOT-5 images on a test site characterized by complex bathymetry (Saint-Pierre, La Réunion Island). A comparison of the retrieved bathymetry with in situ bathymetric measurements reveals good morphological agreement. The mean relative error is less than 30% in the 3-80-m water depth range. The methodological choices made during method development are discussed based on additional computations, and guidelines for using the proposed method on other images at other sites are provided.

Tide gauges are a unique source of information on past sea level changes over the 20thcentury. However, these instruments can be affected by local ground motions, which are often poorly known. Here, InSAR can provide valuable information to understand the ground deformation context at city scale. In this study, we evaluate ground motion velocities from 13 interferograms of 10 Envisat images. Within the precision limitations of the technique, our results suggest that the city of Dakar displays relatively uniform ground motions, except in the harbor. Further investigation is necessary to examine the particular case of a recent tide gauge, which could be affected by a moderate subsidence with respect to the permanent GPS station of Dakar.

CO2injection for storage activity results in ground surface deformation on long periods (several tens on years). Monitoring the evolution of the phenomenon is then required for risk management purposes. Space-borne InSAR can be regarded as an interesting alternative to ground based geodetic techniques (levelling). However, implementing interferometric analysis for the monitoring of surface deformation induced by deep CO2injection is highly hindered by the surface conditions i.e. natural terrains, either agricultural or vegetated areas. Such surface conditions are expected for the future large-scale industrial storage sites. In this presentation we will address the difficulties to adapt the PSI techniques to the specificities of CO2storage activities. We will investigate the characteristics of the monitored deformation and the possibility of improving the PSI method by densifying the PS network with DS and corner reflectors.

Within an effort to estimate near-shore bathymetry from satellite scenes, a method based on wave celerity and wavelength estimation is developed. These wave characteristics are extracted from SPOT-5 panchromatic and multispectral scenes. The method allows us to associate the wavelength and the celerity of the same detected wave and to estimate the water depth from the dispersion relation. This technique is tested on Saint Pierre area (La Reunion Island). Results are compared to in-situ measurements and show a reasonable agreement in terms of morphology and a mean absolute bathymetric error inferior to 30 % in intermediate depths (5-30 m range).

Following Haiti earthquake in January 2010, the French Agence Nationale de la Recherche has funded a project named KAL-Haiti which aims at gathering remote sensing imagery as well as in-situ measurements and exogenous data into a knowledge base. Too often limited to the "response" phase, Earth Observation data should also be available for use by relevant agencies involved throughout the disaster management cycle, from recovery and mitigation to preparedness. The resulting geo-referenced database, seen as a shareable resource, can serve as a basis for helping the reconstruction of the country but also as a reference for scientific studies devoted to all phases of risk management. The database is freely available for scientific studies devoted to the different phases of risk management and for reconstruction tasks in Haiti. KAL-Haiti will also be enriched with new satellite images such as Pleiades, monitoring the evolution of Haiti over the next 10 years.

In this letter, we report the presence of a localized Doppler anomaly occurring during the focusing of a Radarsat-2 data set acquired on the Merapi volcano (Indonesia) during the devastating 2010 eruption. The Doppler anomaly is manifested as ~ 3-km-wide bull's-eye-shaped azimuth pixel shifts between two subaperture images. The Doppler anomaly is centered on the summit-south flank of the Merapi volcano. The pixel shifts reach up to 11.6 m. Since the Merapi volcano was undergoing a large eruption during the data acquisition, it is possible that there is a volcano-related phenomenon that has delayed the radar signal so much to create measurable pixel offsets within a single synthetic aperture radar (SAR) data set, similar, but more extensive, to the signal generated by targets motions; similar, but less extensive, to the signal generated by ionospheric perturbations. It is known that the SAR signal is delayed as it passes through heterogeneous layers of the atmosphere, but this delay typically affects the SAR signal to a fraction of the phase cycle or few centimeters depending on the radar wavelength employed by the system. We investigate the source of this anomalous metric signal; we review the theoretical basis of SAR image focusing, and we try to provide a consistent physical framework to our observations. Our results are compatible with the SAR signal being perturbed during the actual process of image focusing by the presence of a contrasting medium located approximately between 6- and 12.5-km altitude, which we propose being associated with the presence of volcanic ash plume.

Ionospheric contributions to the phase of L-band synthetic aperture radar (SAR) signals put severe limitations on ground displacement measurements retrieved by either differential SAR interferometry or radar amplitude-image offsets. Such contributions result in an ionospheric phase screen on the differential interferogram and in directional fluctuations in the relative position of azimuth pixels on offsets maps. In this letter, we propose a procedure for estimating and removing ionospheric contributions to surface displacement measurements derived from L-band SAR data. We test the procedure on SAR data from the May 28, 2008 Sichuan Earthquake. The applied corrections allow both a clearer interpretation of the surface rupture and a more accurate measurement of the surface displacement, which has important implications in earthquake modeling based on L-band SAR data.