Christine King

Two examples of the use of SAR interferometry on displacement fields of small spatial extent

Interferometric combination of pairs of SAR images acquired by the European ERS-1 satellite maps deformation fields associated with two phenomena, both of small spatial extension and located in SE France: the one is rapid terrain deformation caused by a landslide near the city of Saint Etienne de Tinee, and the other is slower subsidence caused by underground coal mining near Gardanne. Unlike interferometric measurement of wide-field deformation, atmospheric propagation heterogeneity is not an accuracy-limiting factor. Although the radar data confirm prior knowledge concerning the landslide, such an application of SAR interferometry appears difficult under normal conditions of observation using current spaceborne radar systems. The study of soil subsidence, however, can be generalized and improves prior knowledge of the displacement field, which has here been modeled assuming elastic deformation in a half-space from several sources. The two examples help to understand the limits of the interferometric technique.

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

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.

Ground uplift in the city of Paris (France) revealed by satellite radar interferometry

We have analyzed a set of ERS-2 images to investigate centimetric surface deformations within the city of Paris (France) using the radar interferometry technique. We show that a large scale uplift phenomenon occurred during the summer 1998 south of the Saint-Lazare railway station (maximum amplitude of 1.3 cm +/- 0.3 cm). This area corresponds to an important underground working site, which required to lower the piezometric level during 1995 and 1997. The uplift correlates in time with the increase of the underground water level at the end of the construction work. The amplitude of the uplift corresponds to the amplitude of a subsidence which was previously observed in the same area, suggesting that the deformation mechanism is elastic and not simply due to compaction.

Comparison between InSAR and leveling

The Differential SAR Interferometry (DInSAR) technique has been applied to a test site located near Vauvert (France). A subsidence phenomenon has been previously observed by leveling. Precise monitoring of the phenomenon is needed in relation with deep (more than 1 km) exploitation of underground salt by solution mining, in order to constrain further geomechanical modeling studies for a better knowledge of its evolution. The InSAR measurements has been compared to the available leveling data.