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.
Image reconstruction from projections has been extensively developed in the medical field. For example, Computer Assisted Tomography (CAT) scanners measures the absorption of X -rays along ray -projections through a slice of a body. Applying reconstruction algorithms to these projection measurements leads to two or three -dimensional distribution of the mass density. We have applied similar methods which demonstrate image reconstruction from reflective projections obtained with laser radars. These baseband SAR techniques can be applied to any N-dimensional measurements resulting in reconstructions of N + 1-dimensional images. For example, two -dimensional range-Doppler or angle -angle images taken from several views can be reconstructed into three -dimensional images. Shown in this paper, two -dimensional images have been reconstructed from one -dimensional range-time -intensity (RTI) data, Doppler -timeintensity (DTI) data, or a combination of both types of laser radar measurements. Typical RTI measurements can be obtained with either coherent linear FM waveforms, or with incoherent short pulse waveforms. In the DTI case, a cw waveform is sufficient and leads to true narrow -band imaging. We have applied these methods to both computer simulated data and field measurements, at both 10.6 Am and 0.53 µm wavelenghts, using various test targets. ABSTRACT Image reconstruction from projections has been extensively developed in the medical field. For example, Computer Assisted Tomography (CAT) scanners measures the absorption of X-rays along ray-projections through a slice of a body. Applying reconstruction algorithms to these projection measurements leads to two or three-dimensional distribution of the mass density. We have applied similar methods which demonstrate image reconstruction from reflective projections obtained with laser radars. These baseband SAR techniques can be applied to any N-dimensional measurements resulting in reconstructions of N + 1-dimensional images. For example, two-dimensional range-Doppler or angle-angle images taken from several views can be reconstructed into three-dimensional images. Shown in this paper, two-dimensional images have been reconstructed from one-dimensional range-time-intensity (RTI) data, Doppler-timeintensity (DTI) data, or a combination of both types of laser radar measurements. Typical RTI measurements can be obtained with either coherent linear FM waveforms, or with incoherent short pulse waveforms. In the DTI case, a cw waveform is sufficient and leads to true narrow-band imaging. We have applied these methods to both computer simulated data and field measurements, at both 10.6 jitm and 0.53 fim wavelenghts, using various test targets. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 08/17/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx SPIE Vol 999 Laser Radar Ill (1988) / 249 SPIE Vol. 999 Laser Radar III (1988) / 249 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 08/17/2015 Terms of Use: http://spiedigitallibrary.org...
Abstract:The land subsidence which occurs at the Larissa Basin (Thessaly Plain, Central Greece) is due to various causes including aquifer system compaction. Deformation maps of high spatial resolution deduced by the Persistent Scattering Interferometry (PSI) technique (using radar scenes from ERS and ENVISAT satellites) for the period 1992-2006 were produced to study the spatial and temporal ground deformation. A developed GIS database (including geological, tectonic, morphological, hydrological, meteorological and watertable variation from wells in the area) offered the possibility of studying in detail the intense subsidence. The PSI based average deformation image clearly shows that subsidence generally takes place inside the Larissa Plain ranging from 5-250 mm. The largest amplitude rates (-25 mm/yr) are observed around the urban area of Larissa City (especially at Gianouli and Nikea villages), while the Larissa City center appears to be relatively stable with a tendency to subside. The rest of the plain regions seem to subside at moderate rates (about 5-10 mm/yr). The surrounding mountainous area is stable, or has slightly been uplifted with respect to the NE located reference point. It was found that there is a correlation between the seasonal water-table variation (deduced from wells data), the seasonal water demand for irrigation associated with specific types of cultivation (cotton fields), the monthly rainfall, and the observed subsidence rate in the rural regions of the Thessaly Plain.
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