Daniel Raucoules

Detection of mining related ground instabilities using the Permanent Scatterers technique—a case study in the east of France

Ground stability is a major concern for land use planning and both natural and anthropogenic risk assessment, especially in urbanized areas. Space‐borne differential radar interferometry provides a unique tool able to give a synoptic view of ground deformation with centimetric to millimetric vertical precision. Approaches for combining a wide range of radar images such as the permanent scatterers (PS) technique allow the estimation of the deformation history of single buildings. The PS approach has been exploited to investigate a test site particularly exposed to ground deformation hazards, namely the iron mining basin in Lorraine (France). In this Letter, a specific focus was set on the case of Roncourt, where precursor signs of a collapse affecting an area of ∼300×300 m2 have been identified.

Assessing Ionospheric Influence on L-Band SAR Data: Implications on Coseismic Displacement Measurements of the 2008 Sichuan Earthquake

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.

Urban subsidence in the city of Prato (Italy) monitored by satellite radar interferometry

Differential Synthetic Aperture Radar (SAR) interferometry has been widely used to monitor centimetric surface deformations in geophysical applications. In this letter, this technique is applied to study the displacement field in an urban area. A set of six European Remote Sensing satellite (ERS)-1/2 SAR images has been used to detect, map and quantify the subsidence occurring in the city of Prato near Florence (Italy). Four areas which have been affected by strong subsidence during the period 1993-2000 have been spotted within the city. The analysis of three interferograms processed from images taken two years apart shows that the deformation rate appears to be relatively constant, with a maximum value of about 8.3 cm y m 1 .

A Least Squares Adjustment of Multi-temporal InSAR Data: Application to the Ground Deformation of Paris

Satellite radar interferometry can be used to spatially monitor small vertical ground deformations. When millimeter accuracy is required, the differential interferometry technique is hampered by the ambiguity with atmospheric artifacts. It is also often difficult to obtain a precise evaluation of the kinematic evolution of ground deformations from a set of time, randomly distributed interferograms. We present the results of a least-squares approach coupled with a temporal filtering and applied to a large data set over the City of Paris. The mean deformation rate and a map of areas affected by time, non-linear deformation events are presented. We show that this approach, which provides a chronologically ordered set of phase screens, allows the retrieval of the kinematic parameters of ground deformations as low as 1 to 2 mm per year. Subsiding areas have been detected, and their evolution in time has been quantified. Such an approach can be useful to fully characterize the kinematic evolution of ground deformations in major cities

Observation of a Large Landslide on La Reunion Island Using Differential Sar Interferometry (JERS and Radarsat) and Correlation of Optical (Spot5 and Aerial) Images

Slope instabilities are one of the most important geo-hazards in terms of socio-economic costs. The island of La Réunion (Indian Ocean) is affected by constant slope movements and huge landslides due to a combination of rough topography, wet tropical climate and its specific geological context. We show that remote sensing techniques (Differential SAR Interferometry and correlation of optical images) provide complementary means to characterize landslides on a regional scale. The vegetation cover generally hampers the analysis of C–band interferograms. We used JERS-1 images to show that the L-band can be used to overcome the loss of coherence observed in Radarsat C-band interferograms. Image correlation was applied to optical airborne and SPOT 5 sensors images. The two techniques were applied to a landslide near the town of Hellbourg in order to assess their performance for detecting and quantifying the ground motion associated to this landslide. They allowed the mapping of the unstable areas. Ground displacement of about 0.5 m yr-1 was measured.

Subsidence monitoring within the Athens Basin (Greece) using space radar interferometric techniques

The application of conventional SAR Interferometry (InSAR) together with the two techniques of subcentimeter accuracy, the Stacking and the Permanent Scatterers (PS) Interferometry, were used to study the ground deformation in the broader area of Athens for the period 1992 to 2002. Using the Stacking interferometric method, 55 ERS-1&2 SAR scenes, between 1992 and 2002, were acquired producing 264 differential interferograms. Among these only 60 were finally selected as fulfilling certain criteria. The co-seismic deformation associated with the Athens Earthquake (Mw = 5.9, September 7, 1999) was excluded from the analytical procedure in an attempt to present results of only aseismic character. In total ground subsidence results of about 12 mm in the southern suburbs of Athens, but higher value of about 40 mm in the northern ones for the period 1992–2002. Based on the PS technique, a precise average annual deformation rate-map was generated for the period 1992–1999, ending just before the Athens earthquake event. Both circular and elongated-shape areas of subsidence are recognizable especially in the northern part of the Athens Basin (3–4 mm/yr), as well as at its southern part (1–3 mm/yr). In addition, a rate of 2–3 mm/yr is also yielded for some part of the Athens city center. Subsidence rates of 1–2 mm/yr are measured at the western part of the basin over an area of old mining activities, and around the newly built Syntagma Metro Station. The correlation of the observed deformation patterns with respect to the spatial distribution of water pumping, older mining activities, metro line tunneling and other local geological parameters is examined and discussed.

Multisensor Satellite Monitoring of the 2011 Puyehue-Cordon Caulle Eruption

This paper shows the main outcomes of the Puyehue volcano (Chile) eruption monitoring by means of multisensor remote sensing instruments working from thermal infrared (TIR) to microwave (MW) spectral range. Thanks to the use of Synthetic Aperture Radar (SAR) and the Moderate Resolution Imaging Spectroradiometer (MODIS), the eruption evolution was observed, capturing the deformations of volcano edifice, the lava extension, as well as the information on ash and gas emitted. On the one hand, SAR Interferometry applied to ENVISAT-ASAR data allowed the estimation of the deformation occurred just before the beginning of the eruption and the subsequent deflation, with monthly sampling. On the other hand, with the combined use of the very high-resolution (VHR) images taken by COSMO-SkyMed X-band SAR, and ENVISAT-ASAR ones, we were able to follow the lava deposition during the most intense phase of the eruption. Additionally, the joined exploitation of SAR and optical MODIS images allowed ash detection, also in cloudy sky conditions. Finally, the information gathered by both types of sensors allowed to highlight some volcanological features of the eruption and the relationship between surface deformation and the amount of ash and gases emitted by the volcano.

Water depth inversion from satellite dataset

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).

Revisiting the shallow Mw 5.1 Lorca earthquake (southeastern Spain) using C-band InSAR and elastic dislocation modelling

Space geodetic techniques such as interferometric synthetic aperture radar (InSAR) and global positioning systems (GPS) have demonstrated to be useful in mapping the displacement fields of large earthquakes (moment magnitude (Mw) ∼6 or higher). However, the displacement fields of smaller earthquakes (Mw < 5.5), such as those that typically result from the collision of the European and African plates, are less often analysed by space geodetic techniques, and their characterization, in terms of slip along the fault plane at depth and focal depth location, often challenges current seismological techniques. This letter presents the results of InSAR analysis of the 11 May 2011, Mw 5.1, Lorca earthquake. The Lorca earthquake occurred close to an area undergoing rapid subsidence due to sediment compaction related to water pumping. Therefore, it is challenging to separate the InSAR signals due to the earthquake from those due to human activity. We used four sets of SAR data acquired from the European C-band Advanced SAR (ASAR) sensor on board the Environmental Satellite (ENVISAT) to map the surface-displacement field in the Lorca region. Then, we use a simple elastic dislocation model to characterize the fault plane geometry and the fault slip at depth. We find that the InSAR signals can be explained by ∼21 cm reverse slip with a ∼6 cm left-lateral component on a 3 km × 3 km segment centred at 4.2 km depth dipping 45° NW and striking N65° E, consistent with the rupture of a segment of the Alhama de Murcia fault and consistent with recent published analyses. Interestingly, the InSAR signal can also be explained by ∼21 cm reverse slip with a ∼6 cm left-lateral component on a 3 km × 3 km segment centred at ∼4.2 km depth dipping 50° SE and striking N230° E, consistent with preliminary focal plane solutions indicating a rupture on a previously unmapped blind structure. We conclude that the second model cannot be rejected on the base of the InSAR results, the complex surface-displacement pattern (containing both seismic and non-seismic displacement), the different preliminary moment tensor solutions and the published locations of aftershocks at depth.

Water Depth Inversion From a Single SPOT-5 Dataset

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.