Contactless Ground Penetrating Radar Imaging: State of the art, challenges, and microwave tomography-based data processing

Down-Looking Airborne Radar Imaging Performance: The Multi-Line and Multi-Frequency

“…Conversely, whereas the resolution limits do not change, the occurrence of grating lobes depends on the adopted inversion scheme and the presented results state that the TSVD approach allows for improved results compared to the Adjoint, especially when the flight altitude decreases. Herein, the Adjoint inversion has been considered because it is at the basis of the classical imaging methods (see [10]), while the TSVD inversion was been taken into account due to the fact that the singular values are characterized by a slow dynamic before the fast exponential decay [13]. Other regularization inverse schemes might be used especially when the singular values have a smooth decay [13]; this could be an interesting topic of future work.…”

“…Whatever is the considered radar system and the application of interest, a common issue is the design of the measurement configuration as a function of the flight parameters, i.e., flight altitude, number of measurement lines, and number of measurement points along each line. The radar imaging result depends, indeed, on the amount and quality of data as well as on the adopted data processing strategy [9,10]. Moreover, when a UAV radar system is employed, one must account for that, in practice, it is unfeasible to plan a flight grid with a high number of lines spaced by a small, in terms of probing wavelength, spatial offset.…”

An Overview on Down-Looking UAV-Based GPR Systems

“…In most cases, UAV platforms are affected by flight instability. This effect induces defocusing and localization errors in the radar images that impair the detection performances [31]. Moreover, UAV-based GPR technology suffers from a reduced signal penetration with respect to its ground-based counterpart.…”

“…When the measurement points are not equally spaced and the flight trajectory deviates from the ideal rectilinear one, standard GPR-focusing algorithms (e.g., migration [29,30]) cannot be applied, and more sophisticated imaging approaches accounting for UAV positioning information should be exploited [31]. A possible imaging approach is based on a motion compensation (MoCo) procedure.…”

“…The most widely adopted strategies are the Synthetic Aperture Radar (SAR) back-projection method [6,9,14] or f-k migration [29,30]. Another relevant focusing strategy worth mentioning is the microwave tomography (MWT) approach based on the solution of a linear inverse scattering problem [31].…”