3D Database

One of the strength of Institut Fresnel in Marseille, France, is the tight coupling which exists between experiments and theory. This is how came out the idea, inspired by the Ipswich database [1-4], of designing a new database containing results of controlled scattering experiments and make it available to the inverse problems community, thus giving to the researchers a further opportunity of testing and validating their inversion algorithms against reliable experimental data. The experiments have been carried out in the anechoic chamber of the Centre Commun de Ressources Micro-Ondes (CCRM), managed for this topic by the researchers of Institut Fresnel. This anechoic chamber is one of the microwave measurement setups that the Institut is developing.

The first opus
In the special section from Inverse Problems entitled "Testing inversion algorithms against experimental data" [5], first results were reported through 10 contributions from several research teams. For this inaugural opus, elongated homogeneous targets, such to be assumed as two dimensional, were measured within a multi-frequency multi-static configuration. Detailed description of the measurement arrangement specific to this opus can be found in the introduction of the special section [5]. The experimental data are free for scientific use and can be downloaded.
The second opus
The success of the first opus was an encouragement to go further on and to design new challenges for the inverse scattering community. Taking into account the remarks formulated by several colleagues, a second dataset was provided with "infinitely" long inhomogeneous targets measured in both Transverse Electric and Transverse Magnetic polarizations. This led to the second special section from Inverse Problems entitled "Testing inversion algorithms against experimental data: inhomogeneous targets" [6]. In this latter, 11 contributions from several research teams were included, reporting on a large diversity of inversion scattering techniques exploited to successfully reconstruct the profile of the inhomogeneous objects. Detailed description of the measurement configuration specific to this opus can be found in [7]. The experimental data is again free for scientific use and can be downloaded.
The third opus
Then, the next step was to extend the database towards full three-dimensional (3D) problems, which represent the current challenge for the inverse scattering community. To this aim, a large effort has been carried out to be able to measure the scattered fields of 3D targets, which were meaningful and yet computationally affordable. This has led to consider objects that, especially at the lower frequencies, were small as compared to the wavelength, thus posing the challenge of performing measurements characterized by a very low signal-to-noise ratio. Hence, several improvements have been obtained on the measurement system itself, as well as on the data processing part [8] [9] [10], making it possible the extension of the database to 3D targets.
For this third opus, entitled "Testing inversion algorithms against experimental data: 3D targets", the scattered fields of five dielectric targets have been measured, amongst them a mysterious target, whose estimated position and overall size was only known to the experimental team. More details on the measurement procedure and on the targets can be found in [11]. 6 contributions from several research teams are gathered in this special session [12], and highlight the way they have used the known targets to test and calibrate their inversion schemes before tackling the mysterious one.

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The next opus ?
For the time being there are no session planned. Nevertheless, if anyone is interested in obtaining scattering measurements of exotic targets, the best is to directly contact J.-M. Geffrin .

References

[1] R.V. McGahan and R.E. Kleinman, Special session on image reconstruction using real data, IEEE Antennas and Propagations 38, pp. 39-59 (1996)

[2] R.V. McGahan and R.E. Kleinman, Second annual special session on image reconstruction using real data, IEEE Antennas and Propagations 39, pp. 7-32 (1997)

[3] R.V. McGahan and R.E. Kleinman, Third annual special session on image reconstruction using real data: part 1, IEEE Antennas and Propagations 41, pp. 34-51 (1999)

[4] R.V. McGahan and R.E. Kleinman, Third annual special session on image reconstruction using real data: part 2, IEEE Antennas and Propagations 41, pp. 20-40 (1999)

[5] K. Belkebir, M. Saillard, "Special section on testing inversion algorithms against experimental data", Inverse Problems 17, pp. 1565-1571 (2001)

[6] K. Belkebir, M. Saillard, "Special section on testing inversion algorithms against experimental data: Inhomogeneous targets", Inverse Problems 21, pp. S1-S3 (2005)

[7] J.-M. Geffrin, P. Sabouroux, C. Eyraud, "Free space experimental scattering database continuation: experimental set-up and measurement precision", Inverse Problems 21, pp. S117-S130 (2005)

[8] C. Eyraud, J.-M. Geffrin, A. Litman, P. Sabouroux, H. Giovannini, "Drift correction for scattering measurements", Applied Physics Letters 89, 244104 (2006)
Copyright(2006) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters and may be found at http://link.aip.org/link/?APL/89/244104.

[9] C. Eyraud, J.-M. Geffrin, P. Sabouroux, P.C. Chaumet, H. Tortel, H. Giovannini, A. Litman , "Validation of a 3d bistatic microwave scattering measurement setup" Radio Sci. 43 RS4018 (2008)

[10] J.-M. Geffrin, C. Eyraud, A. Litman, P. Sabouroux, "Optimization of a bistatic microwave scattering measurement setup: from high to low scattering targets" Radio Sci. RS003837 (2009)

[11] J.-M. Geffrin, P. Sabouroux, "Continuing with the Fresnel database: experimental setup and improvements in 3D scattering measurements", Inverse Problems 25 024001(2009)

[12] A. Litman, L. Crocco, " Testing inversion algorithms against experimental data: 3D targets", Inverse Problems 25 020201 (2009)