Ullmann Ingrid, Vossiek Martin
Institute of Microwaves and Photonics, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany.
Sensors (Basel). 2023 Nov 7;23(22):9021. doi: 10.3390/s23229021.
In classical radar imaging, such as in Earth remote sensing, electromagnetic waves are usually assumed to propagate in free space. However, in numerous applications, such as ground penetrating radar or non-destructive testing, this assumption no longer holds. When there is a multi-material background, the subsurface image reconstruction becomes considerably more complex. Imaging can be performed in the spatial domain or, equivalently, in the wavenumber domain (k-space). In subsurface imaging, to date, objects with a non-planar surface are commonly reconstructed in the spatial domain, by the Backprojection algorithm combined with ray tracing, which is computationally demanding. On the other hand, objects with a planar surface can be reconstructed more efficiently in k-space. However, many non-planar surfaces are partly planar. Therefore, in this paper, a novel concept is introduced that makes use of the efficient k-space-based reconstruction algorithms for partly planar scenarios, too. The proposed algorithm forms an image from superposing sub-images where as many image parts as possible are reconstructed in the wavenumber domain, and only as many as necessary are reconstructed in the spatial domain. For this, a segmentation scheme is developed to determine which parts of the image volume can be reconstructed in the wavenumber domain. The novel concept is verified by measurements, both from monostatic synthetic aperture radar data and multiple-input-multiple-output radar data. It is shown that the computational efficiency for imaging irregularly shaped geometries can be significantly augmented when applying the proposed concept.
在经典雷达成像中，例如在地球遥感中，通常假设电磁波在自由空间中传播。然而，在许多应用中，如探地雷达或无损检测，这一假设不再成立。当存在多材料背景时，地下图像重建会变得相当复杂。成像可以在空间域进行，或者等效地，在波数域（k空间）进行。在地下成像中，迄今为止，具有非平面表面的物体通常在空间域中通过结合射线追踪的反投影算法进行重建，这对计算要求较高。另一方面，具有平面表面的物体可以在k空间中更有效地重建。然而，许多非平面表面部分是平面的。因此，本文引入了一种新颖的概念，该概念也利用基于k空间的高效重建算法来处理部分平面的情况。所提出的算法通过叠加子图像来形成图像，其中尽可能多的图像部分在波数域中重建，而仅在空间域中重建必要数量的部分。为此，开发了一种分割方案来确定图像体积的哪些部分可以在波数域中重建。通过对单基地合成孔径雷达数据和多输入多输出雷达数据的测量验证了这一新颖概念。结果表明，应用所提出的概念时，对不规则形状几何结构成像的计算效率可以显著提高。
