A Near-Field 3d Circular Sar Imaging Technique Based on Spherical Wave Decomposition

Abstract

Abstract-A near-field three dimensional imaging algorithm for circular SAR is proposed in this paper. It adopts the theory of spherical wave decomposition to transform Green function to a superposition of plane wave components. Using this relation, the image-reconstruction can be implemented in frequency domain instead of in spatial domain, which simplifies the solving process of target reflectivity function, and allows for the target to be near to the radar. Through compensating phase factor and filtering at each elevation, we firstly get the ground CSAR signal of each elevation in frequency domain. Then, performing two dimensional inverse nonuniform fast Fourier transform and accumulating the results of all azimuth angles, the reconstructed two dimensional image corresponding to an elevation is achieved. Finally, using reconstructed image datum of all elevation, the three dimensional image of target is obtained. To demonstrate the imaging performance of our method, numerical simulations and experiments are conducted. By comparing the results with the focusing operator algorithm and the back-projection algorithm, it is found that the proposed algorithm is more efficient and can obtain a good imaging performance.

High-Resolution Grid-Independent Imaging for Terahertz 2-D Synthetic Aperture Radar With Spatial Under-Sampling

“…Terahertz (THz) benefited from its low radiation energy, strong penetration and high resolution has spurred a surge of interests into the imaging fields, especially into the security-related applications [1][2][3][4][5][6].…”

“…Although SAR is a well-known technique trading time for space in the microwave imaging region [7,8], many geometries of inversion problems can be seen as interesting variants of SAR, such as the transceiver array in [9] by trading cost for time. For the imaging method, Fourier transform (FT), which is widely used in the classical microwave SAR fields, is also a way of well-known imaging in the THz band [2][3][4][5][6]. [3] has proposed a surveillance system with a vertical linear antenna array actuated over a circular path to obtain a 360 • cylindrical scan, and similarly for such a SAR with circular trajectory, [4] has provided a nonuniform FT-based algorithm to decrease the computation complexity.…”

“…For the imaging method, Fourier transform (FT), which is widely used in the classical microwave SAR fields, is also a way of well-known imaging in the THz band [2][3][4][5][6]. [3] has proposed a surveillance system with a vertical linear antenna array actuated over a circular path to obtain a 360 • cylindrical scan, and similarly for such a SAR with circular trajectory, [4] has provided a nonuniform FT-based algorithm to decrease the computation complexity. Operating at difference THz band, [5] has elaborated the outcomes obtained by a 2-D planar SAR with broadband sweep signals, while [6] has proposed an imaging scheme based on frequency-controlled beam scanning antenna to speed up the scene scanning.…”

“…One of the most important factors is the shorter wavelength of THz radiation, which implies the reduced sampling interval in space. In order to utilize FT, spatial sampling should obey Nyquist theory to obtain a full set of data [3,4]. This leads to a larger amount of data and dramatically increases the signal acquisition time.…”

Efficient Terahertz Wide-Angle NUFFT-Based Inverse Synthetic Aperture Imaging Considering Spherical Wavefront

“…Also, these methods usually use sub-apertures or sub-images to make approximations, which impacts the accuracy of the compensation. In circular synthetic aperture radar (CSAR), there are also several reports on the wavefront curvature problem [17], and piecewise planar approximation [18] and spherical wave decomposition [19,20] techniques are utilized. However, the accuracy and computational efficiency of these methods are still not satisfactory.…”