Vertical movements of the Earth’s crust occur both on short and long time scales. Over short time... more Vertical movements of the Earth’s crust occur both on short and long time scales. Over short time scales, vertical motions are affected by loading effects induced by environmental parameter variations, such as for example, meteoclimatic factors and the hydrological cycle. Over long time scales, several geological processes are responsible for height changes. These can be locally enhanced by anthropogenic factors. Natural subsidence affects most of the eastern Po Plain, in Italy. In addition, along the northwestern Adriatic coast, groundwater withdrawal during the second half of last century has greatly increased the subsidence rate. The comparison of the results provided by different high-precision observing techniques, namely continuous GPS (CGPS), InSAR and high-precision leveling has been performed at Marina di Ravenna, a coastal site on the Adriatic. The data relevant to the last decade have been analyzed and intercompared in order to achieve mutual calibration and validation of the results. While CGPS allows a high temporal resolution, daily or sub-daily solutions, InSAR, although not having the same temporal resolution, allows the characterization of surficial indicators of tectonic activity and/or crustal movements with spatial resolution higher than that achievable with CGPS. Repeated leveling data are available for this area because regional/local agencies are charged with the monitoring of the local subsidence. The results provided by the three techniques will be shown.
... The peculiar blade-like shape of the power spectrum asso-ciated with ionospheric phase screen... more ... The peculiar blade-like shape of the power spectrum asso-ciated with ionospheric phase screens affecting a LEO SAR results in all visible phase screen components to be captured by employing the optimal integration time. ...
The problem of range or azimuth variations in Doppler centroid is analyzed. The defocusing effect... more The problem of range or azimuth variations in Doppler centroid is analyzed. The defocusing effects caused by an incorrect Doppler centroid estimation are discussed. It is shown that efficiency frequency domain focusing techniques can be exploited, provided that SAR (Synthetic Aperture Radar) raw data is previously modified and a space varying nondimensional filter is applied to the focused image. The computational cost increased but was smaller than for space domain processing. Results obtained with simulated computer data and spot-light geometries are presented and show that Doppler centroid variations in azimuth due to platform instability, and rapid Doppler centroid variations with range due to Earth rotation, can be easily processed.
Satellite differential synthetic aperture radar interferometry (DInSAR) is an attractive techniqu... more Satellite differential synthetic aperture radar interferometry (DInSAR) is an attractive technique for detecting and monitoring ground surface deformations arising from regional scale processes (e.g. seismic/volcanic). The technique, however, is not effective for site-specific evaluations, because of coarse resolution and coherence loss limitations. Permanent Scatterers interferometry (PSInSAR), developed at Politecnico di Milano and improved at T.R.E. s.r.l. company, overcomes the limitations of DInSAR and extends the applicability of radar interferometry to local-scale geotechnical investigations of slope instability and soil settlement/ground subsidence. The PSInSAR analysis allows the identification of numerous radar targets (the PS) where very precise displacement information can be obtained. Considering the regular re-visit time and wide-area coverage of satellite radar sensors, and that PS usually correspond to buildings and other man-made structures, this technique is particularly suitable for applications in urban environments, which often represent a harsh setting for GPS or conventional topographic surveying.
Notwithstanding the advances in InSAR due to the introduction of the Permanent Scatterer (PS) app... more Notwithstanding the advances in InSAR due to the introduction of the Permanent Scatterer (PS) approach in the late nineties, some limitations still remain, especially in applications related to Civil Protection. Interestingly enough, one of the major blockages is related to the space segment rather then the data-processing stage. The lack of a regular acquisition of SAR data over the area of interest and the difficulties related to lack of interferometric data after the ERS-2 gyro-failure and before the start of a regular acquisition of ENVISAT ASAR scenes often represents a severe obstacle to provide reliable answers to decision-makers in charge of land management. Despite the limits mentioned above, many applications related to surface deformation monitoring and with a huge potential impact on Civil Protection tasks can already benefit from radar space measurements. As it will be discussed, historical data can be a key element for hazard map generation and for quick information recovery on the dynamics of unstable areas. Fast updating of the PS archive could represent a breakthrough in monitoring risky areas. The interferometric Radarsat data-set over Italy (more than 30 scenes already acquired over the whole country) created thanks to TRE investments can give a major contribution to studies related to volcanic and seismogenetic areas, supporting and integrating ESA-Envisat acquisitions. The last part of the presentation will be devoted to the future of this technology, the new SAR sensors that will be launched in 2006 (namely Radarsat-2, TerraSAR-X, Cosmo-SkyMed and ALOS-PALSAR) and the new ESA missions related to the GMES program. For sure, in the near future, different SAR sensors will be jointly exploited to extract information not only for the scientific community but also for other users such as Civil Protection authorities and Public Administrations in charge of land management.
Annals of Gis Geographic Information Sciences, Jun 1, 2010
Space-borne synthetic aperture radar interferometry (INSAR) is a well-known widely used remote se... more Space-borne synthetic aperture radar interferometry (INSAR) is a well-known widely used remote sensing technique to get precise (to the millimeter) surface deformation measurements on large areas (thousands of square kilometers) and high spatial density of measurement points (hundreds per square kilometer). A short review of the INSAR basics is dedicated to the readers who are not INSAR specialists. Then, an
IGARSS 2001. Scanning the Present and Resolving the Future. Proceedings. IEEE 2001 International Geoscience and Remote Sensing Symposium (Cat. No.01CH37217), 2000
The difficulties related to InSAR DEM reconstruction and the computational burden necessary to ge... more The difficulties related to InSAR DEM reconstruction and the computational burden necessary to get the final result strongly depend on the topography of the area of interest and accuracy requirements. Whenever high quality results are requested, a multi-interferograrn approach is strongly recommended, especially for repeat-pass interferometric data, such as ERS Tandem acquisitions. In this paper we recall the rationale of
With this paper we investigate the structural and polarimetric of the boreal forest within the Kr... more With this paper we investigate the structural and polarimetric of the boreal forest within the Krycklan river catchment, Northern Sweden, basing on multi-polarimetric and multi-baseline SAR surveys at P-Band and L-Band collected in the framework of the ESA campaign BioSAR 2008. The analysis has been carried out by applying the Algebraic Synthesis (AS) technique, recently introduced in literature, which provides a theoretical framework for the decomposition of the backscattered signal into ground-only and volume-only contributions, basing on both baseline and polarization diversity. The availability of multiple baselines allows the formation of a synthetic aperture not only along the azimuth direction but also in elevation. Accordingly, the backscattered echoes can be focused not only in the slant range, azimuth plane, but in the whole 3D space. This is the rationale of the SAR Tomography (T-SAR) concept, which has been widely considered in the literature of the last years. It follows that, as long as the penetration in the scattering volume is guaranteed, the vertical profile of the vegetation layer is retrieved by separating backscatter contributions along the vertical direction, which is the main reason for the exploitation of Tomographic techniques at longer wavelengths. Still, the capabilities of T-SAR are limited to imaging the global vertical structure of the electromagnetic scattering in a certain polarization. It then becomes important to develop methodologies for the investigation of the vertical structure of different Scattering Mechanisms (SMs), such as ground and volume scattering, in such a way as to derive information that can be delivered also outside the field of Radar processing. This is an issue that may become relevant at longer wavelengths, such as P-Band, where the presence of multiple scattering arising from the interaction with terrain could hinder the correct reconstruction of the forest structure. The availability of multiple polarizations allows to overcome this limitation, thus providing a way to obtain the vertical structures associated with volume-only contributions. Experimental results will be provided showing the following. At P-Band the most relevant scattering contributions are observed at the ground level, not only in the co-polar channels, but also in HV, consistently with he first BioSAR campaign. L-Band data have shown a remarkable difference, resulting in a more uniform distribution of the backscattered power along the vertical direction. Volume top height has been observed to be substantially invariant to the choice of the solution for volume-only scattering. These results underline the validity of modeling a forest scenario as being constituted by volume and ground (or rather ground-locked) scattering, and the importance of forest top height as the most robust indicator of the forest structure as imaged through microwaves measurements. Nevertheless, it has also been shown that different solutions for volume scattering correspond to dramatically different vertical structures. In this framework, tomography represents a powerful tool for investigating the potential solutions, as it allows to see what kind of vertical structure has been retrieved. On this basis, a solution has been proposed as a criterion to emphasize volume contributions at P-Band.
Vertical movements of the Earth’s crust occur both on short and long time scales. Over short time... more Vertical movements of the Earth’s crust occur both on short and long time scales. Over short time scales, vertical motions are affected by loading effects induced by environmental parameter variations, such as for example, meteoclimatic factors and the hydrological cycle. Over long time scales, several geological processes are responsible for height changes. These can be locally enhanced by anthropogenic factors. Natural subsidence affects most of the eastern Po Plain, in Italy. In addition, along the northwestern Adriatic coast, groundwater withdrawal during the second half of last century has greatly increased the subsidence rate. The comparison of the results provided by different high-precision observing techniques, namely continuous GPS (CGPS), InSAR and high-precision leveling has been performed at Marina di Ravenna, a coastal site on the Adriatic. The data relevant to the last decade have been analyzed and intercompared in order to achieve mutual calibration and validation of the results. While CGPS allows a high temporal resolution, daily or sub-daily solutions, InSAR, although not having the same temporal resolution, allows the characterization of surficial indicators of tectonic activity and/or crustal movements with spatial resolution higher than that achievable with CGPS. Repeated leveling data are available for this area because regional/local agencies are charged with the monitoring of the local subsidence. The results provided by the three techniques will be shown.
... The peculiar blade-like shape of the power spectrum asso-ciated with ionospheric phase screen... more ... The peculiar blade-like shape of the power spectrum asso-ciated with ionospheric phase screens affecting a LEO SAR results in all visible phase screen components to be captured by employing the optimal integration time. ...
The problem of range or azimuth variations in Doppler centroid is analyzed. The defocusing effect... more The problem of range or azimuth variations in Doppler centroid is analyzed. The defocusing effects caused by an incorrect Doppler centroid estimation are discussed. It is shown that efficiency frequency domain focusing techniques can be exploited, provided that SAR (Synthetic Aperture Radar) raw data is previously modified and a space varying nondimensional filter is applied to the focused image. The computational cost increased but was smaller than for space domain processing. Results obtained with simulated computer data and spot-light geometries are presented and show that Doppler centroid variations in azimuth due to platform instability, and rapid Doppler centroid variations with range due to Earth rotation, can be easily processed.
Satellite differential synthetic aperture radar interferometry (DInSAR) is an attractive techniqu... more Satellite differential synthetic aperture radar interferometry (DInSAR) is an attractive technique for detecting and monitoring ground surface deformations arising from regional scale processes (e.g. seismic/volcanic). The technique, however, is not effective for site-specific evaluations, because of coarse resolution and coherence loss limitations. Permanent Scatterers interferometry (PSInSAR), developed at Politecnico di Milano and improved at T.R.E. s.r.l. company, overcomes the limitations of DInSAR and extends the applicability of radar interferometry to local-scale geotechnical investigations of slope instability and soil settlement/ground subsidence. The PSInSAR analysis allows the identification of numerous radar targets (the PS) where very precise displacement information can be obtained. Considering the regular re-visit time and wide-area coverage of satellite radar sensors, and that PS usually correspond to buildings and other man-made structures, this technique is particularly suitable for applications in urban environments, which often represent a harsh setting for GPS or conventional topographic surveying.
Notwithstanding the advances in InSAR due to the introduction of the Permanent Scatterer (PS) app... more Notwithstanding the advances in InSAR due to the introduction of the Permanent Scatterer (PS) approach in the late nineties, some limitations still remain, especially in applications related to Civil Protection. Interestingly enough, one of the major blockages is related to the space segment rather then the data-processing stage. The lack of a regular acquisition of SAR data over the area of interest and the difficulties related to lack of interferometric data after the ERS-2 gyro-failure and before the start of a regular acquisition of ENVISAT ASAR scenes often represents a severe obstacle to provide reliable answers to decision-makers in charge of land management. Despite the limits mentioned above, many applications related to surface deformation monitoring and with a huge potential impact on Civil Protection tasks can already benefit from radar space measurements. As it will be discussed, historical data can be a key element for hazard map generation and for quick information recovery on the dynamics of unstable areas. Fast updating of the PS archive could represent a breakthrough in monitoring risky areas. The interferometric Radarsat data-set over Italy (more than 30 scenes already acquired over the whole country) created thanks to TRE investments can give a major contribution to studies related to volcanic and seismogenetic areas, supporting and integrating ESA-Envisat acquisitions. The last part of the presentation will be devoted to the future of this technology, the new SAR sensors that will be launched in 2006 (namely Radarsat-2, TerraSAR-X, Cosmo-SkyMed and ALOS-PALSAR) and the new ESA missions related to the GMES program. For sure, in the near future, different SAR sensors will be jointly exploited to extract information not only for the scientific community but also for other users such as Civil Protection authorities and Public Administrations in charge of land management.
Annals of Gis Geographic Information Sciences, Jun 1, 2010
Space-borne synthetic aperture radar interferometry (INSAR) is a well-known widely used remote se... more Space-borne synthetic aperture radar interferometry (INSAR) is a well-known widely used remote sensing technique to get precise (to the millimeter) surface deformation measurements on large areas (thousands of square kilometers) and high spatial density of measurement points (hundreds per square kilometer). A short review of the INSAR basics is dedicated to the readers who are not INSAR specialists. Then, an
IGARSS 2001. Scanning the Present and Resolving the Future. Proceedings. IEEE 2001 International Geoscience and Remote Sensing Symposium (Cat. No.01CH37217), 2000
The difficulties related to InSAR DEM reconstruction and the computational burden necessary to ge... more The difficulties related to InSAR DEM reconstruction and the computational burden necessary to get the final result strongly depend on the topography of the area of interest and accuracy requirements. Whenever high quality results are requested, a multi-interferograrn approach is strongly recommended, especially for repeat-pass interferometric data, such as ERS Tandem acquisitions. In this paper we recall the rationale of
With this paper we investigate the structural and polarimetric of the boreal forest within the Kr... more With this paper we investigate the structural and polarimetric of the boreal forest within the Krycklan river catchment, Northern Sweden, basing on multi-polarimetric and multi-baseline SAR surveys at P-Band and L-Band collected in the framework of the ESA campaign BioSAR 2008. The analysis has been carried out by applying the Algebraic Synthesis (AS) technique, recently introduced in literature, which provides a theoretical framework for the decomposition of the backscattered signal into ground-only and volume-only contributions, basing on both baseline and polarization diversity. The availability of multiple baselines allows the formation of a synthetic aperture not only along the azimuth direction but also in elevation. Accordingly, the backscattered echoes can be focused not only in the slant range, azimuth plane, but in the whole 3D space. This is the rationale of the SAR Tomography (T-SAR) concept, which has been widely considered in the literature of the last years. It follows that, as long as the penetration in the scattering volume is guaranteed, the vertical profile of the vegetation layer is retrieved by separating backscatter contributions along the vertical direction, which is the main reason for the exploitation of Tomographic techniques at longer wavelengths. Still, the capabilities of T-SAR are limited to imaging the global vertical structure of the electromagnetic scattering in a certain polarization. It then becomes important to develop methodologies for the investigation of the vertical structure of different Scattering Mechanisms (SMs), such as ground and volume scattering, in such a way as to derive information that can be delivered also outside the field of Radar processing. This is an issue that may become relevant at longer wavelengths, such as P-Band, where the presence of multiple scattering arising from the interaction with terrain could hinder the correct reconstruction of the forest structure. The availability of multiple polarizations allows to overcome this limitation, thus providing a way to obtain the vertical structures associated with volume-only contributions. Experimental results will be provided showing the following. At P-Band the most relevant scattering contributions are observed at the ground level, not only in the co-polar channels, but also in HV, consistently with he first BioSAR campaign. L-Band data have shown a remarkable difference, resulting in a more uniform distribution of the backscattered power along the vertical direction. Volume top height has been observed to be substantially invariant to the choice of the solution for volume-only scattering. These results underline the validity of modeling a forest scenario as being constituted by volume and ground (or rather ground-locked) scattering, and the importance of forest top height as the most robust indicator of the forest structure as imaged through microwaves measurements. Nevertheless, it has also been shown that different solutions for volume scattering correspond to dramatically different vertical structures. In this framework, tomography represents a powerful tool for investigating the potential solutions, as it allows to see what kind of vertical structure has been retrieved. On this basis, a solution has been proposed as a criterion to emphasize volume contributions at P-Band.
In this paper we discuss a preliminary design for a constellation of geosynchronous (GEO) Synthet... more In this paper we discuss a preliminary design for a constellation of geosynchronous (GEO) Synthetic Aperture Radars (SAR). The key design concept is to employ one or more pairs of closely-spaced twin receivers flown onboard GEO minisatellites moving with a velocity of few meters per second with respect to the Earth's surface, so as to form a synthetic aperture on the order of few tenths of kilometers twice a day. The employement of closely-spaced receivers would enable the estimation of the temporal gradient of the tropospheric delay via along track Interferometry, resulting in the possibility to coherently integrate the signal over an aperture time on the order of hours. As a result an area as wide as one thousand kilometers could be imaged while providing: i) continuous temporal coverage at coarse resolution (hundreds of meters); ii) high resolution (few meters) imaging and interferometric capabilities two or more times a day by integrating the signal over few hours, thus ensuring high SNR performance (for stable targets) with a transmitted power comparable to currently operated spaceborne SARs.
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Papers by Fabio Rocca