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On the selection of the best polarization to detect buried objects by means of POLINSAR

Dr Juan M Lopez-Sanchez (1)and Carolina Pascual(1)

(1) University of Alicante, P.O. Box 99, E-03080 Alicante, Spain

Abstract

In this work, we analyze some questions about the potential application of polarimetric SAR interferometry (POLINSAR) in ground penetrating radar (GPR) systems. GPR is based on the ability of electromagnetic waves in the microwave region to penetrate the matter. However, the detection performance of these systems is only acceptable when looking for large metallic objects. Buried plastic mines are nearly invisible to the radar and can not be detected due to the low dielectric contrast between the mine and the surrounding soil. The weak signal returned from the mine is normally obscured by the terrain clutter. POLINSAR can be used to combine the three polarimetric channels of two images obtained from different incidence angles, in order to look for coherence peaks in the scene. This technique can retrieve these peaks even if some scattering centers are present in the same resolution cell, or if their backscatter levels are very different. The application of POLINSAR to the detection of buried objects was already introduced in [1] and [2]. The optimization of the interferometric coherence, carried out by POLINSAR at every resolution cell, produces three coherences associated with three scattering mechanisms or polarizations. It was shown in [2] that, in the presence of mines, one of these mechanisms corresponds to the surface clutter and a different one is located at the mine. Each mechanism is identified by a change in the polarization basis, which in turn can be interpreted by projection vectors [3] or by angles in the polarization ellipse [2]. In this work we have reviewed which polarizations are the optimum to detect mines by means of POLINSAR. This preliminary study shows that circular polarizations (or nearly circular) are always useful to discriminate the mine from the clutter. Therefore, instead of carrying out the full POLINSAR optimization, we have proceed to compute coherence maps of the scene by employing this type of polarization. First experimental results with real polarimetric data indicate that the coherence maps exhibit very low values in the positions of the mines, whereas the coherence is quite high in the rest. So, this parameter can be applied to detect mines. A physical interpretation of these results is currently in progress. Moreover, the minimum signal-to-clutter ratio necessary to detect the mine is being investigated.

References:

[1] S.R. Cloude and K.P. Papathanassiou, 'Polarimetric Radar Interferometry and Its Applications', in Proc. of PIERS Workshop on Advances in Radar Methods, pp. 61-63, Baveno, Italy, July 1998.

[2] L. Sagués, J.M. López, J. Fortuny, X. Fàbregas, A. Broquetas, A.J. Sieber, 'Polarimetric Radar Interferometry for Improved Mine Detection and Surface Clutter Rejection', IEEE Trans. Geosci. Remote Sensing, vol. 39, No. 6, pp. 1271-1278, June 2001.

[3] S.R. Cloude and K.P. Papathanassiou, 'Polarimetric SAR Interferometry', IEEE Trans. Geosci. Remote Sensing, vol. 36, No. 5, pp. 1551-1565, September 1998.

 

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