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Analysis of Urban Areas Scattering with Simulated SAR imagery

Gerard Margarit(1), Jordi J. Mallorquí(1) and Carlos Lopez-Martinez(1)

(1) Universitat Politecnica de Catalunya, C Jordi Girona, 1-3, E-08034, Barcelona, Spain

Abstract

The proliferation of new orbital/air-borne SAR missions with improved resolutions and polarimetric / interferometric capabilities has been recently increased the range of applications where SAR imagery would be useful. One of these areas is urban environment. Up to now, few studies have been performed due to the limitations of current SAR systems for dealing with the high density of small scale objects contained within the scenes. This trend is nowadays changing and the new generation of SAR sensors is improving the available data in terms of system coverage, revisiting time, resolution and information channels (polarimetry + interferometry). This situation has increased the volume and quality of the available information demanding new methodologies for properly interpreting it. One of the main topics is the analysis of the scattering response of urban areas. The idea is to define accurate connections between the measured reflectivity SAR response and the observed geometry so that classification / identification procedures may be improved and inversion algorithms of physical parameters developed. In this context, the evaluation of the system requirements (in special the interferometric ones) demanded for properly exploiting SAR sensors in urban environments is also important.

This paper will evaluate these issues. For such purpose, a high amount of simulated scattering maps are analyzed for different observation conditions. These images are obtained from the SAR simulator of 3D complex targets (GRECOSAR), which is based on high-frequency electromagnetic methods [1]. This simulator can synthesize any SAR sensor for any resolution and operating mode with polarimetric and interferometric capabilities. The scenario can assume different aspect angles and material information, despite ground information generating surrounding clutter is not available yet. In the past, GRECOSAR has been successfully used in ship classification and identification. There, the analysis of different images has allowed to improve the knowledge of ship scattering and, thus, define proper reflectivity-geometry relations. As a result, a new identification algorithm based on Polarimetric Interferometric SAR (PolInSAR) data and with reliable behaviour for real-like observation conditions has been defined [2-3]. Now, this experience will be used in urban areas following the same work plan than in vessels. The main goal lies on evaluating the scattering information of different buildings for diversified ranges of views and find if classification methods are possible and, in affirmative case, which parameters should be exploited.

In this paper, both Inverse SAR and InSAR images are analyzed. Their imaging geometries are defined in such way that the scattering information from both modes can be linked. The scenario accounts for a complex model of a building where interferometric real measurements have been performed with a Ground-Based SAR sensor. The data collected by this sensor in different measurement campaigns are used here to interpret the simulated one. Two conclusions are important, namely: 1) the scattering response of the building appears to be stable along the aspect angle, but less stable along time dimension where the influence of human activity may modify the results; and 2) the analysis of single-pass PolInSAR datasets with Coherent Target Decompositions theorems and height inversion techniques have shown that it is possible to retrieve 3D scattering maps that summarizes the geometry of buildings. These maps may have under certain conditions sub-pixel accuracy (according to the polarimetric mechanisms) and they have appeared to be a reasonable product for basing a classification approach.

1.G. Margarit, J. J. Mallorqui, J. M. Rius, and J. Sanz-Marcos, “On the usage of GRECOSAR, an orbital polarimetric SAR simulator of complex targets, for vessel classification studies,” IEEE Trans. Geosci. Remote Sensing, vol. 44, no. 12, pp. 3517–3526, Dec. 2006.

2.G. Margarit, J. J. Mallorqui, and X. Fabregas, “Single-pass polarimetric SAR interferometry for vessel classification,” IEEE Trans. Geosci. Remote Sensing, Accepted to the EUSAR Special Issue.

3.Gerard Margarit, Jordi J. Mallorqui, Juan M. Rius, Jesus Sanz-Marcos and Xavier Fabregas, “Orbital Single-pass interferometry for vessel detection and classification”, ESA FRINGE 2005 Workshop

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry