Paolo Pasquali

A comparison of phase to height conversion methods for SAR interferometry

SAR interferometry has been shown capable of producing accurate digital elevation models. InSAR height map generation always includes a transformation from the unwrapped phase to terrain height. Various methods for carrying out this step have been presented in the literature. This paper compares the different methods using both synthetic and real data for spaceborne and airborne geometries. The systematic errors introduced by each algorithm are analyzed. For each method, both the necessary number of parameters, as well as their required accuracies are evaluated with the goal of minimizing the required number of ground control points. The impact of the choice of geometry on the differential InSAR case is also investigated.

Algorithms for calculation of digital surface models from the unwrapped interferometric phase

The focus of this paper is on interferometric DEM generation algorithms from imaging geometry analysis. The proper description of the interferometric imaging geometry is presented. As a result of solving the two sets of range-Doppler equations one also obtains the interferometric alongtrack baseline component. This fixes the imaging positions of each pixel in the case of known antenna tracks. Conversely, if the relative positions of the antenna tracks are not precisely known, one may adjust the interferometric baseline by comparing the azimuth-offsets from image correlation to the calculated alongtrack baseline. As an example, the angle of convergence is estimated using single-pass interferometric DOSAR data motion compensated to individual reference tracks. A new method of estimating the absolute phase difference is suggested which exploits the range-offsets obtained from correlating the complex image pair. Finally, it is shown that layover produces a residual tilt in interferometric DEMs if the crosstrack-coordinate is left unfiltered.

MERIS Atmospheric Water Vapor Correction Model for Wide Swath Interferometric Synthetic Aperture Radar

A major source of error for repeat-pass interferometric synthetic aperture radar is the phase delay in radio signal propagation through the atmosphere, particularly the part due to tropospheric water vapor. These effects become more significant for ScanSAR observations due to their wider coverage (e.g., 400 km × 400 km for ENVISAT Advanced Synthetic Aperture Radar (ASAR) wide swath (WS) mode versus 100 km × 100 km for ASAR image mode). In this letter, we demonstrate for the first time that a Medium Resolution Imaging Spectrometer water vapor correction model can significantly reduce atmospheric water vapor effects on ASAR WS interferograms, with the phase variation in non-deforming areas decreasing from 3.8 cm before correction to 0.4 cm after correction.

Height model generation, automatic geocoding and a mosaicing using airborne AeS-1 InSAR data

The goal of this paper is to present the generation of high resolution digital surface models using airborne AeS-1 interferometric SAR data, their automatic geocoding and mosaicing. In order to be able to carry out these steps, high precision differential Global Positioning System data, high frequency attitude data of the platform, exact time synchronization and range delay of the system must be known. Since in the airborne case motion instabilities are large, due to dynamic properties of the aircraft and atmospheric turbulences, precise motion measurements of the platform are extracted and considered during the SAR processing. Once that all these basic requirements are fulfilled, one is able, using the processing reference tracks, and exploiting a forward-backward geocoding, to convert the phase differences to elevation data and to geolocate them by taking into account all geodetic and cartographic transforms. Results based on 400 MHz X-band InSAR data show that the derived surface model has a positioning accuracy in the order of 0.5 m and a height accuracy better than 0.3 m.

Building Damage Risk by Modeling Interferometric Time Series

Predicting building damage due to subsidence phenomena is a great challenge in the field of risk management, and moreover in the process of disaster risk reduction. The proposed damage assessment integrates measurements obtained from satellite synthetic aperture radar (SAR) observations with a semiempirical model, which schematizes buildings as equivalent laminated beams. The importance of each of the parameters involved in the semiempirical method has been evaluated to understand the applicability of the model in different urban contexts. SAR monitoring and structural modeling have been connected to investigate a densely urban area, the southern part of the city of Rome. Information obtained from the two fields allowed for the generation of risk maps.

Synergetic use of multi-temporal ALOS PALSAR and ENVISAT ASAR data for topographic/land cover mapping and monitoring at national scale in Africa

The use of Synthetic Aperture Radar (SAR) data in large parts of the African countries, in particular for those close to the equator, is often conditio sine qua non, simply due to the fact that optical data are severely hampered by clouds, especially during the raining (corresponding to the crop) season. The objective of this paper is to present a methodology — and the related results — for the generation of land cover maps and changes over large areas by fusing single-date or interferometric ALOS PALSAR Fine/Dual Beam data with multi-temporal ENVISAT ASAR Image Mode/Alternating Polarization intensity. In synthesis, the method is based on data fusion by exclusively considering — in the prior knowledge-based classifier that requires neither user-defined parameters nor reference samples — the data characteristics and related acquisition modes. Results clearly show that the synergetic use enables the reliable identification of key land cover types (in particular cropped areas, bare soil areas, forestry, forest clear cut, forest burnt areas, water bodies) and their evolution over time, providing basic information on the land cover status. Finally, it is shown that using the same 46-days interferometric ALOS PALSAR data set, a Digital Elevation Model (DEM) with higher quality than the Shuttle Radar Topographic Mission (SRTM) one can be generated in those nearly equatorial — non dense forest — regions.

Calibration and classification of SIR-C polarimetric and interferometric SAR data in areas with slope variations

The goal of this paper is to present the capabilities and the limitations of SIR-C SAR magnitude data (dual frequency, dual polarization) and dual frequency interferometric SAR data for land cover classification purposes in areas with slope variations. The work consists of three parts. In a first step SIR-C SAR magnitude HH-, HV-polarized data acquired during the SRL-2 mission (DT 110.00) over an area with terrain ranging from hilly to mountainous (around 1800 sq. km) in Central Switzerland is geometrically and radiometrically calibrated, considering scattering area variations and radiometric errors due to topographic effects on the antenna gain pattern. After this step the backscattering coefficient is classified using a supervised method taking a-priori information into account (thematic and topographic information). In a second step, repeat-pass SIR-C InSAR VV-polarized data (DT 142.12 and 158.12) acquired 24 hours later over the same site is interferometrically processed. In order to correct the interferometric phase for slope variations and therefore to improve the coherence estimation the InSAR data is terrain geocoded. Only after these calibration steps can the backscattering coefficient and coherence data be qualitatively and quantitatively analysed.

Risk of building damage by modeling interferometric time series

Predicting building damages due to ground movements caused by subsidence phenomena is a great challenge in the field of Risk Management, moreover in the process of Disaster Risk Reduction. This damage assessment integrates measurements obtained from satellite SAR observations with an intermediate semi-empirical model, which schematizes buildings as equivalent laminated beams. The monitoring and modelling stages have been embedded to investigate densely urban areas. Two test sites have been examined: the Southern part of the city of Rome (Italy) and a recently constructed building in Astana (Kazakhstan). Furthermore, the importance of each of the parameters involved in the semi-empirical method for modelling building deformation has been evaluated to understand the applicability of the modelling in different urban contexts, with different knowledge of the urban pattern.

Damage assessment in buildings affected by subsidence using SAR data and interferometric stacking techniques in Rome

Predicting building damages due to ground movements caused by subsidence phenomena is a great challenge in the field of Risk Management, moreover in the process of Disaster Risk Reduction. This damage assessment integrates measurements obtained from satellite SAR observations with an intermediate semi-empirical model, which schematizes buildings as equivalent laminated beams. These two fields have been connected to best investigate and to present accurate results on a densely urban area, in the specific the Southern part of the city of Rome (Italy).

Monitoring Small land Subsidence Phenomena in the Al-Ain Region by Satellite SAR Interferometric Stacking

Some areas of the United Arab Emirates suffered from subsidence, cavities and related problems,[0]. Subsidence and, in general, surface land deformations and displacement phenomena, typically involve large regions in the geographical meaning. For such regions, in principle, the terrain displacements should be monitored with an accuracy that is in the orders of magnitude smaller than the spatial resolution: one measurement every several meters should bring an accuracy of few centimetres or even millimetres. Not many technologies can nowadays provide such a combination. One of the few is Synthetic Aperture Radar Interferometry, and all related developments, that can, generally, be identified as Advanced Interferometric or Interferometric Stacking techniques. This paper presents one case study in Al-Ain region (UAE) by exploiting Interferometric Stacking techniques to monitor land displacements in the order of few millimetres per year.