Abstract
For detection of a two-layered rough surface structure through ground-penetrating radar, the estimation of the profile of each layered rough surface is an important problem to be solved. In modeling and calculating the scattering of two-layered rough surfaces, we found that the profile of the upper rough surface can be observed directly through the figure of the echo from the upper surface. However, the echo of the lower rough surface has a quite different shape from its surface profile, because of the influence of the scattering of the upper rough surface. This is disadvantageous to the estimation and imaging of the profile of the lower rough surface. To solve this problem, a time-delay calibration method is proposed in this paper to be applied to the profile estimation of the lower rough surface in the case of two-layered rough interface detection. By introducing a smooth surface, the expression of time delay is derived to eliminate the influence of the scattering of the upper surface. Applying the derived expression of time delay to the echo data from the lower rough surface, the echo outline of the lower rough surface can be corrected to reflect the surface's profile shape. The calibrated B-scan echo shape shows good agreement with the profile of the lower rough surface. With this method, we can get the profile shape of the lower rough surface quickly and simply by calibrating the echo data directly. This method can be used for fast microwave imaging of two-layered rough surface and for eliminating the interference of scattering from rough surface on the echoes of nearby targets. The purpose of this paper is to solve the problem we have found in our previous work. The work of this paper is an extension of the previous work.
Highlights
Microwave detection of a layered structure with rough interfaces attracts many scholars’ attention because of its wide applications [1]–[5], such as probing of underground rock and soil structure by ground penetrating radar (GPR) [1], [4], civil engineering [2], sea surface [3], [5], medical microwave imaging, road subgrade detection, and so on
In our previous work of analysis on GPR echo from the underground layered rough interfaces [17], we found that the echo from the top rough surface shows the same shape with its surface profile, but the lower rough surfaces cannot reflect the surface profiles
We found that regardless of the changes in roughness, the echo shape of the upper surface is always the same with the profile of the upper rough surface
Summary
Microwave detection of a layered structure with rough interfaces attracts many scholars’ attention because of its wide applications [1]–[5], such as probing of underground rock and soil structure by ground penetrating radar (GPR) [1], [4], civil engineering [2], sea surface (snow covered sea ice) [3], [5], medical microwave imaging, road subgrade detection, and so on. We present a timedelay calibration method in this paper to estimate the profile of the lower rough surface in the two-layered rough surface structure This method can eliminate the influence of the scattering of the upper surface on the echo shape of the lower surface by directly adjusting the time delay. To make the echo of lower surface reflect the surface profile, it is necessary to calibrate the difference in the initial time of propagation in the lower layer of media due to the ups and downs of the upper rough surface. This is the main idea of the time-delay calibration method. To ensure the accuracy of the time-delay calibration method, a priori knowledge of the dielectric constant of the layered structure is needed
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