On the selection of the best polarization to detect buried objects by means of POLINSAR
University of Alicante,
P.O. Box 99,
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  and . 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  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  or by angles in the
polarization ellipse . 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.
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.
 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.
 S.R. Cloude and
K.P. Papathanassiou, 'Polarimetric SAR Interferometry', IEEE Trans. Geosci.
Remote Sensing, vol. 36, No. 5, pp. 1551-1565, September 1998.