| Ground Penetrating Radar (GPR) is one of the most feasible and friendly instrumentation to detect buried remains and perform diagnostics of archaeological structures with the aim of detecting hidden objects (defects, voids, constructive typology; etc..). In fact, GPR technique allows to perform measurements over large areas in a very fast way thanks to a portable instrumentation.
Despite of the widespread exploitation of the GPR as data acquisition system, many difficulties arise in processing GPR data so to obtain images reliable and easily interpretable by the end-users. This difficulty is exacerbated when no a priori information is available as for example arises in the case of historical heritages for which the knowledge of the constructive modalities and materials of the structure might be completely missed.
A possible answer to the above cited difficulties resides in the development and the
exploitation of microwave tomography algorithms [1, 2], based on more refined electromagnetic
scattering model with respect to the ones usually adopted in the classic radaristic approach.
By exploitation of the microwave tomographic approach, it is possible to gain accurate and reliable “images” of
the investigated structure in order to detect, localize and possibly determine the extent and the geometrical features of the embedded objects.
In this framework, the adoption of simplified models of the electromagnetic scattering
appears very convenient for practical and theoretical reasons. First, the linear inversion
algorithms are numerically efficient thus allowing to investigate domains large
in terms of the probing wavelength in a quasi real- time also in the case of 3D case also by adopting schemes based on the combination of 2D reconstruction [3]. In addition, the solution approaches are very robust against the uncertainties in the parameters of the measurement configuration and on the investigated scenario.
From a theoretical point of view, the linear
models allow further advantages such as: the absence of the false solutions (a question
to be arisen in non linear inverse problems); the exploitation of well known regularization
tools for achieving a stable solution of the problem; the possibility to analyze
the reconstruction performances of the algorithm once the measurement configuration
and the properties of the host medium are known.
Here, we will present the main features and the reconstruction results of a linear inversion algorithm based on the Born approximation in realistic applications in archaeology and cultural heritage diagnostics. Born model
is useful when penetrable objects are under investigations. As well known, the Born
Approximation is used to solve the forward problem, that is the determination of the
scattered field from a known object under the hypothesis of weak scatterer, i.e. an object
whose dielectric permittivity is slightly different from the one of the host medium
and whose extent is small in term of probing wavelength. Differently, for the inverse
scattering problem, the above hypotheses can be relaxed at the cost to renounce to
a “quantitative reconstruction” of the object. In fact, as already shown by results in
realistic conditions [4, 5], the adoption of a Born model inversion scheme allows to
detect, to localize and to determine the geometry of the object also in the case of not weak scattering objects.
[1] R. Persico, R. Bernini, F. Soldovieri, “The role of the measurement configuration
in inverse scattering from buried objects under the Born approximation”, IEEE Trans.
Antennas and Propagation, vol. 53, no.6, pp. 1875-1887, June 2005.
[2] F. Soldovieri, J. Hugenschmidt, R. Persico and G. Leone, “A linear inverse scattering
algorithm for realistic GPR applications”, Near Surface Geophysics, vol. 5, no. 1,
pp. 29-42, February 2007.
[3] R. Solimene, F. Soldovieri, G. Prisco, R.Pierri, “Three-Dimensional Microwave Tomography by a 2-D Slice-Based Reconstruction Algorithm”, IEEE Geoscience and Remote Sensing Letters, vol. 4, no. 4, pp. 556 – 560, Oct. 2007.
[4] L. Orlando, F. Soldovieri, “Two different approaches for georadar data processing: a case study in archaeological prospecting”, Journal of Applied Geophysics, vol. 64, pp. 1-13, March 2008.
[5] F. Soldovieri, M. Bavusi, L. Crocco, S. Piscitelli, A. Giocoli, F. Vallianatos, S. Pantellis, A. Sarris, “A comparison between two GPR data processing techniques for fracture detection and characterization”, Proc. of 70th EAGE Conference & Exhibition, Rome, Italy, 9 - 12 June 2008 |