Leping Chen

A Backprojection-Based Imaging for Circular Synthetic Aperture Radar

Circular synthetic aperture radar (CSAR) has attracted much attention in the field of high-resolution SAR imaging. However, the CSAR image focusing is affected by the motion deviations of platform. In the processing of experimental CSAR data to deal with motion errors, the main way is using setup calibrators, which restricts its widespread applications. In this paper, based on the estimation of motion errors, an autofocus CSAR imaging strategy is proposed without using any setup calibrator. The first step is to split the entire aperture into several subapertures, the second step is to process the data in subapertures with an autofocus backprojection method, and the last step is to obtain the final CSAR image by merging the subimages obtained from the subaperture processing. The CSAR data processing results prove that the proposed strategy can remove the motion errors accurately and acquire well-focused CSAR images.

Fast time-domain focusing for low frequency UWB circular SAR data

Low frequency ultra wideband (UWB) synthetic aperture radar (SAR) has shown a great potential when vehicle-size objects are obscured in foliage. This study presents fast factorized back projection algorithm (FFBPA) for low frequency UWB circular synthetic aperture radar (CSAR). This method is based on strip-map FFBPA. First, the imaging geometry of the CSAR is given. Then, based on the subaperture imaging model, the sampling requirements of the subimage polar grid are derived from FFBPA. Finally, simulation results are shown to demonstrate its validity.

P-band ultra wideband circular synthetic aperture radar experiment and imaging

Low frequency ultra wideband (UWB) synthetic aperture radar (SAR) has shown a great potential when vehicle-size objects are obscured in foliage. The studies imply an aperture angle of at least 180° to include the strongest (broadside) response when the target orientations are unknown. However, the aperture angle of the linear SAR (LSAR) is limited. By using circular traces, the aperture angle of the radar data acquisition has been increased, and the detection capabilities could be improved. An airborne circular SAR (CSAR) data acquisition experiment was carried out in Shaanxi by the National University of Defense Technology (NUDT). The data was acquired by using P-band UWB SAR system along a circular trajectory with the beam spotted on the same area. Compared with LSAR, this imaging mode has a better understanding of the scattering properties of targets, high resolution with low frequency band, and the capability for a 3-D target reconstruction. In this paper, the airborne multiple orbit CSAR data acquisition experiment and the processing of such data are presented.

Modified nonlinear chirp scaling algorithm for one-stationary bistatic low frequency ultrawideband synthetic aperture radar imaging

Abstract. We outline a modified nonlinear chirp scaling algorithm (NLCSA) for one-stationary bistatic synthetic aperture radar (BiSAR) using low-frequency (LF) and an ultrawideband (UWB) signal. The existing NLCSAs for one-stationary BiSAR will be invalidated in an LF and UWB application because the higher-order phase error (HOPE) due to the Taylor series approximation cannot be ignored in this case. We first analyze the effect of the HOPE on bistatic LF UWB SAR imaging theoretically. Then, a modified method based on the higher-order phase compensation (HOPC) and block processing is proposed to deal with the HOPE. Finally, the simulation results demonstrate the correctness of the theory analyses, and the validity of the proposed algorithm is presented.

Extended Autofocus Backprojection Algorithm for Low-Frequency SAR Imaging

Since the trajectory deviations of a radar platform cause serious phase errors that degrade the focusing quality of synthetic aperture radar (SAR) imagery, an autofocus method is very important for high-resolution airborne SAR imaging. In this letter, an extended autofocus backprojection (EABP) algorithm is developed to accommodate the phase errors. Under the criterion of maximum image sharpness, the traditional ABP algorithm supports a broader class of collection and imaging geometries. However, it neglects the influence of SAR image energy distribution on the estimation of phase errors that make it inapplicable for SAR imaging, which has high dynamic range, such as low-frequency SAR imaging. By choosing regions and balancing the energy distribution of the data, the EABP algorithm is more efficient and useful to avoid the estimation error caused by the unbalanced energy distribution. Its performance has been demonstrated by using the experimental data that are acquired by a P-band airborne SAR system with a low-accuracy global positioning system.

A 3D Reconstruction Strategy of Vehicle Outline Based on Single-Pass Single-Polarization CSAR Data

In the last few years, interest in circular synthetic aperture radar (CSAR) acquisitions has arisen as a consequence of the potential achievement of 3D reconstructions over 360° azimuth angle variation. In real-world scenarios, full 3D reconstructions of arbitrary targets need multi-pass data, which makes the processing complex, money-consuming, and time expending. In this paper, we propose a processing strategy for the 3D reconstruction of vehicle, which can avoid using multi-pass data by introducing a priori information of vehicle’s shape. Besides, the proposed strategy just needs the single-pass single-polarization CSAR data to perform vehicle’s 3D reconstruction, which makes the processing much more economic and efficient. First, an analysis of the distribution of attributed scattering centers from vehicle facet model is presented. And the analysis results show that a smooth and continuous basic outline of vehicle could be extracted from the peak curve of a noncoherent processing image. Second, the 3D location of vehicle roofline is inferred from layover with empirical insets of the basic outline. At last, the basic line and roofline of the vehicle are used to estimate the vehicle’s 3D information and constitute the vehicle’s 3D outline. The simulated and measured data processing results prove the correctness and effectiveness of our proposed strategy.In the last few years, interest in circular synthetic aperture radar (CSAR) acquisitions has arisen as a consequence of the potential achievement of 3D reconstructions over 360° azimuth angle variation. In real-world scenarios, full 3D reconstructions of arbitrary targets need multi-pass data, which makes the processing complex, money-consuming, and time expending. In this paper, we propose a processing strategy for the 3D reconstruction of vehicle, which can avoid using multi-pass data by introducing a priori information of vehicles shape. Besides, the proposed strategy just needs the single-pass single-polarization CSAR data to perform vehicles 3D reconstruction, which makes the processing much more economic and efficient. First, an analysis of the distribution of attributed scattering centers from vehicle facet model is presented. And the analysis results show that a smooth and continuous basic outline of vehicle could be extracted from the peak curve of a noncoherent processing image. Second, the 3D location of vehicle roofline is inferred from layover with empirical insets of the basic outline. At last, the basic line and roofline of the vehicle are used to estimate the vehicles 3D information and constitute the vehicles 3D outline. The simulated and measured data processing results prove the correctness and effectiveness of our proposed strategy.

Extended factorized geometrical autofocus for circular synthetic aperture radar processing

This paper introduces an extended factorized geometrical autofocus (FGA) algorithm for circular synthetic aperture radar (CSAR) which is based on the FGA in stripmap synthetic aperture radar (SAR). The strategy is that integrate the FGA with a fast factorized back-projection (FFBP) processing chain and relies on varying track parameters step by step to obtain the sharp image. The focused quality of the obtained image is evaluated by computing an object function (intensity correlation). The algorithm has been tried out on a wavelength-resolution CSAR data set with erroneous track parameters. To set up constrained problems, only one track parameter is corrupted. The FGA imaging results are compared with the reference imaging results, demonstrating its excellent capacity of compensating platform trajectory movement deviation.

P band UWB CSAR vehicle experiment and raw data processing

In circular synthetic aperture radar (CSAR), targets are usually scanned over the complete azimuthal aperture of 360°. Thus CSAR can provide a higher image resolution, increased object information and 3-D imaging in comparison to the linear SAR system. This paper presents a low frequency ultra-wideband CSAR experiment and results. The CSAR system, operating in the P band, is based on a P band UWB SAR system integrated onboard a vehicle (IVECO). For the measurement campaign is a near field imaging, the transmitter and the receiver is bistatic, which are set on the top of the IVECO separately. A measurement campaign was conducted to investigate the performance of the low frequency UWB CSAR imaging and scattering characteristics of complex vehicle target. A CSAR imaging method, which is based on fast factorized back projection (FFBP), is proposed to focusing near field data, and the reconstructed images are cleaned out from clutter to more easily visualize the layover artifacts.

Three dimensional electromagnetic model guided scattering center extraction

Scattering center extraction from Synthetic Aperture Radar (SAR) data is a critical step in model-based SAR automatic target recognition (ATR). Three dimensional electromagnetic model (3D em-model) provides a concise and physically relevant description of targets electromagnetic scattering behavior by a set of representative scattering centers. In this paper, 3D em-model is used to guide scattering center extraction in SAR data. Firstly, 3D em-model is projected to the 2D measurement plane to predict the scattering region and the attributed parameters of each scattering center. Then, scattering center is extracted in the corresponding region predicted by 3D em-model with the model predicted parameters as an initial guess. Finally, a search strategy is adopted to optimize the scattering region and find the optimal parameters. Experiments using data simulated by a high-frequency electromagnetic code verify the validity of this method.

Research on resolution of bistatic forward-looking SAR based on spatial wavenumber of the point target

In this paper, a novel method of spatial resolution analysis for low frequency (LF) ultra-wideband (UWB) bistatic forward-looking SAR (BFSAR) is presented, which is based on the wavenumber domain spectrum support of point target. First, the imaging geometry and signal model of the LF UWB BFSAR are established, and the wavenumber domain spectrum support of the point target is analyzed. Then, the analytical expression of the spatial resolution of LF UWB BFSAR is derived. Finally, the simulation experiment is carried out, and the results prove the correctness and validity of the proposed method of spatial resolution analysis.