RF Tomography for Below-Ground Imaging of Extended Areas and Close-in Sensing

Abstract

Three extensions to RF Tomography for imaging of voids under extended areas of regard are presented.These extensions are motivated by three challenges. One challenge is the lateral wave, which propagates in proximity of the air-earth interface, and represents the predominant radiation mechanism for wide area surveillance, sensing of denied terrains, or close-in sensing. A second challenge is the direct path coupling between Tx and Rx, that affects the measurements. A third challenge is the generation of clutter by the unknown distribution of anomalies embedded in the ground.These challenges are addressed and solved using the following strategies: 1) A forward model for RF Tomography that includes lateral waves expressed in closed-form (for fast computation); 2) a strategy that reduces the direct-path coupling between any Tx-Rx pair; 3) an improved inversion scheme that is robust with respect to noise, clutter, and high attenuation.An FDTD simulation of a scenario representing close-in sensing of a denied area is performed, and reconstructed images obtained using the improved and the classical model of RF Tomography are compared.

A Comprehensive Forward Model for Imaging under Irregular Terrain Using RF Tomography

“…The following sections extend the work proposed in [2], which was itself a generalization of [1,[7][8][9][10][11][12][13][14][15][16], to the general case of electric/magnetic sources and electric/magnetic probes.…”

“…The functions G u (r, r ) represent the Green's function specific for the half-space geometry (having planar interface at z = 0), whereas G S u (r, r ) represent the scattered contribution due to the presence of the background contrast function Q defined in (2). Analytical expressions of the half-space Green's function G(r, r ) do exist in several forms [5,[7][8][9][10][11][12]; however, in Appendix, we propose better formulas that are explicit, easy to be integrated, and computed with FFT, and having very…”

“…The data is noiseless; however, discrepancies between the numerical FDTD solver and the proposed MoM-based method can be assumed as unknown perturbation of the measured field, thus implicitly testing the robustness of our algorithm with respect to disturbances. The reconstruction has been performed using a modified FISTA algorithm; details can be found in [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]21].…”

“…Chew and Cui presented an approach to compute halfspace dyadic Green's function based on vector wave functions expressed in Cartesian form [7][8][9][10][11][12][22][23][24][25][26][27][28][29][30][31][32][33][34] and several manipulations to obtain less singular solutions. In this work, International Journal of Antennas and Propagation their spirit is used to explicitly calculate the half-space dyadic Green's functions needed in RF tomography.…”

Tunnel detection and localisation via multi-monostatic radio frequency tomography using magnetic sources

“…Future research activities will be concerned with the extension of the proposed approaches to the improved multi-view/multistatic configuration [5][6][7] and the adoption of approaches able to account the inherent sparseness of the ground-penetrating radar scenario [33] with the aim to estimate the geometry of the target with more accuracy and resolution. …”