Shilong Sun

Linearized 3-D Electromagnetic Contrast Source Inversion and Its Applications to Half-Space Configurations

One of the main computational drawbacks in the application of 3-D iterative inversion techniques is the requirement of solving the field quantities for the updated contrast in every iteration. In this paper, the 3-D electromagnetic inverse scattering problem is put into a discretized finite-difference frequency-domain scheme and linearized into a cascade of two linear functionals. To deal with the nonuniqueness effectively, the joint structure of the contrast sources is exploited using a sum-of-

A Linear Model for Microwave Imaging of Highly Conductive Scatterers

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A Linear Method for Shape Reconstruction Based on the Generalized Multiple Measurement Vectors Model

-norm optimization scheme. A cross-validation technique is used to check whether the optimization process is accurate enough. The total fields are, then, calculated and used to reconstruct the contrast by minimizing a cost functional defined as the sum of the data error and the state error. In this procedure, the total fields in the inversion domain are computed only once, while the quality and the accuracy of the obtained reconstructions are maintained. The novel method is applied to ground-penetrating radar imaging and through-the-wall imaging, in which the validity and the efficiency of the method are demonstrated.

Cross-Correlated Contrast Source Inversion

In this paper, a linear model based on multiple measurement vectors’ model is proposed to formulate the inverse scattering problem of highly conductive objects at one single frequency. Considering the induced currents that are mostly distributed on the boundaries of the scatterers, joint sparse structure is enforced by a sum-of-norm regularization. Since no a priori information is required and no approximation of the scattering model has been made, the proposed method is versatile. Imaging results with transverse magnetic and transverse electric polarized synthetic data and Fresnel data demonstrate its higher resolving ability than both linear sampling method and its improved version with higher, but acceptable, computational complexity.

Simultaneous multi-frequency TE/TM polarization inversion based on FDFD for ground penetrating radar

In this paper, a novel linear method for shape reconstruction is proposed based on the generalized multiple measurement vectors’ (GMMVs) model. Finite-difference frequency domain is applied to discretize Maxwell’s equations, and the contrast sources are solved iteratively by exploiting the joint sparsity as a regularized constraint. Cross validation technique is used to terminate the iterations, such that the required estimation of the noise level is circumvented. The validity is demonstrated with an excitation of transverse magnetic experimental data, and it is observed that, in the aspect of focusing performance, the GMMV-based linear method outperforms the extensively used linear sampling method.

Real GPR signal processing for target recognition with circular array antennas

In this paper, we improved the performance of the contrast source inversion (CSI) method by incorporating a so-called cross-correlated cost functional, which interrelates the state error and the data error in the measurement domain. The proposed method is referred to as the cross-correlated CSI. It enables better robustness and higher inversion accuracy than both the classical CSI and multiplicative regularized CSI (MR-CSI). In addition, we show how the gradient of the modified cost functional can be calculated without significantly increasing the computational burden. The advantages of the proposed algorithms are demonstrated using a 2-D benchmark problem excited by a transverse magnetic wave as well as a transverse electric wave, respectively, in comparison with classical CSI and MR-CSI.

Inversion of Multifrequency Data With the Cross‐Correlated Contrast Source Inversion Method

In Ground Penetrating Radar (GPR), inversion techniques like Contrast Source Inversion (CSI) have been applied extensively. In this paper, CSI is applied to handle 2D TE/TM-polarized excitations, in which the form for the TE-polarized Maxwell operator is equivalent to the 3D Maxwell operator. Furthermore, a simultaneous TE/TM polarization CSI method based on Finite Difference Frequency Domain (FDFD) together with a frequency hopping scheme is proposed, in which FDFD is able to handle heterogeneous background media. 2D simulation results verify the advantage of the proposed inversion scheme. Since the proposed method is based on a 2D Maxwell operator which has a similar form as the 3D Maxell operator, it can be extended to a 3D CSI-scheme straightforwardly.

Processing the experimental fresnel data by the GMMV-based shape reconstruction method

In this paper, 3D imaging of forward-looking Ground Penetrating Radar (GPR) data acquired by rotating antennas have been done. The data acquisition procedure mimics data collection of the Tunnel Boring Machine (TBM). Real GPR data for a Karst scenario were analyzed, preprocessed and finally imaged with back-projection method. Results show that objects buried in the subsurface of the ground can be successfully imaged using rotating antennas, which is a solid foundation for further development of the GPR system on TBM.

Solving the PEC inverse scattering problem with a linear model

Cross-correlated contrast source inversion (CC-CSI) is a nonlinear iterative inversion method that is proposed recently for solving the inverse scattering problems. In CC-CSI, a cross-correlated error is constructed and introduced to the cost functional, which improves the inversion ability when compared to the classical design of the cost functional by exploiting the mismatch between the data error and state error. In this paper, the multifrequency inversion for electromagnetic waves is considered and a multifrequency version of CC-CSI is proposed. Numerical and experimental inversion results of both transverse magnetic and transverse electric polarization demonstrate that when multifrequency data are available, CC-CSI still outperforms the multiplicative-regularized CSI method in the inversion of more complicated scatterers.

A generalized electromagnetic wave penetrating propagation model for CS imaging in through-the-wall radar

This paper presents the application of the shape reconstruction method based on the generalized multiple measurement vectors (GMMV) model on the multi-frequency transverse magnetic (TM) and transverse electric (TE) polarized Fresnel data, measured by the Institue Fresnel (Marseille, France) from cylindrical objects. Finite difference frequency domain (FDFD) is applied to discretize the Maxwells equations, and the contrast sources are solved iteratively by exploiting the joint sparsity as a regularized constraint. Cross validation (CV) technique is used to terminate the iterations and give the estimation of the noise level at the same time. The results show that the GMMV-based linear method successfully performs shape reconstruction of a large variety of scatterers.