The polar format algorithm (PFA) is a frequency-domain algorithm with high computational efficiency especially for the high resolution imaging applications in wide-angle staring synthetic aperture radar (WAS-SAR). Because of the image distortion and defocus caused by plane wave assumption, the effective imaging scene is limited to a small region which is defined as the defocus-negligible region. In this article, a novel sub-block imaging algorithm which first applied to WAS-SAR is proposed. This method combines sub-block imaging and spatially variant post-filtering (SVPF) which can not only effectively extend the depth of focus of PFA but also greatly reduces the computational burden. What's more, the method of mosaic image is proposed in this article which can eliminate discontinuity between adjacent sub-blocks. First, the large scene is segmented into multiple regions along range direction and the size of each region is still larger than that of the defocus-negligible region. Second, refocusing is implemented by a phase compensation of the already de-chirped signal with the center of sub-blocks, respectively, and each sub-block image is formed by PFA. Third, the region in each sub-block that exceeds the defocus-negligible region is corrected by SVPF and the image distortion can be corrected by 2-D interpolation. Finally, the mosaic image method is applied to get the large-scene image with high quality. The algorithm proposed in this article is efficient and solves the problems in the process of SAR image mosaic such as dislocation and grayscale differences. The simulated and experimental data results demonstrate the effectiveness and practicability of the proposed algorithm.

As a new observation mode, wide-angle staring synthetic aperture radar ground moving target indication (WasSAR-GMTI) which can observe the fixed area for a long time and achieve moving target tracking has attracted a lot of interest. However, with increasingly complex flight trajectories and application scenarios, the performance of traditional method tends to degrade. In this paper, a novel approach based on post-Doppler space-time adaptive processing (PD-STAP) and imaging method is proposed. Firstly, selecting and extending training data from repeat-pass data can obtain accuracy estimated clutter covariance matrix (CCM). Moreover, the relationship between extended quantity of training data and clutter suppression performance is further analyzed in this paper. And then, the joint-pixel PD-STAP (JP PD-STAP) which utilizing auxiliary units under test cell along range direction is performed to overcome the effect of residual range curvature after keystone transform (KT). Finally, after clutter suppression, the parameters and imaging method based on WasSAR system is proposed. The multidimensional parameter is simplified as 1-D line search problem which has high efficiency. Considering the curvilinear trajectory, the Back-Projection (BP) is adopted to processed. Inserting parameters into BP can be seen as coarse motion compensation (MOCO), the further spectrum compression (SC) method and phase gradient autofocus (PGA) is performed to obtain refocus and relocate imaging of moving target. The real-measured WasSAR data processing results demonstrated the effectiveness and practicability of the proposed algorithm.

Multi-channel wide-angle staring synthetic aperture radar ground moving target indication (WasSAR-GMTI) has attracted a lot of interest for its ability of moving target detection and trajectory reconstruction. However, the parameter estimation of moving target is easily affected by clutter and noise which deteriorate the performance of the following geo-location. In this paper, a novel approach for trajectory reconstruction of moving target based on road line is proposed. Firstly, after performing multi-channel calibration, a novel Doppler centroid estimation and correction method is proposed. This method is not depended on attitude information of platform, nor does it require scene uniformity as a prior condition, which has high robustness in complex environment. And then, the weighted adaptive matched filtering (WAMF) and modified Gaussian mixture probability hypothesis density (GMPHD) is performed for velocity estimation and tracking. Last, the error items affecting geo-location accuracy were analyzed in detail. And a novel two-step geo-location method based on road line is proposed to correct geo-location error which can be applied in complex road network. The proposed method only needs one-dimensional parameter searching which has high efficiency. The real-measured WasSAR data processing results demonstrated the effectiveness and practicability of the proposed algorithm.

With the continuous development of synthetic-aperture-radar (SAR) technology, SAR-image data are becoming increasingly abundant. For the same scene, dual-frequency (high-frequency and low-frequency) SAR images can present different details and feature information. Image fusion of the two frequencies can combine the advantages of both, thus describing targets more comprehensively. Image registration is the key step of image fusion and determines the quality of fusion. Due to the complex geometric distortion and gray variance between dual-frequency SAR images with high resolution, it is difficult to realize accurate registration between the two. In order to solve this problem, this paper proposes a method to achieve accurate registration by combining edge features and gray information. Firstly, this paper applies the edge features of images and a registration algorithm based on fast Fourier transform (FFT) to realize rapid coarse registration. Then, combining a registration algorithm based on the enhanced correlation coefficient (ECC) with the concept of segmentation, the coarse-registration result is registered to achieve accurate registration. Finally, by processing the airborne L-band and Ku-band SAR data, the correctness, effectiveness, and practicability of the proposed method are verified, with a root mean square error (RMSE) of less than 2.

Video synthetic aperture radar (ViSAR) can provide long-time surveillance of a region of interest (ROI), which is one of the hotspot directions in the SAR field. In order to better display ViSAR, a high resolution and high frame rate are needed. Azimuth integration angle and sub-aperture overlapping ratio, which determine the image resolution and frame rate, respectively, are analyzed in depth in this paper. For SAR imaging algorithm, polar format algorithm (PFA) is applied, which not only has high efficiency but is also easier to integrate with autofocus algorithms. Due to sensitivity to motion error, it is very difficult to obtain satisfactory focus quality, especially for SAR systems with a high carrier frequency. The three-step motion compensation (MOCO) proposed in this paper, which combines GPS-based MOCO, map-drift (MD) and phase gradient autofocus (PGA), can effectively compensate for motion error, especially for short wavelengths. In ViSAR, problems such as jitter, non-uniform grey scale and low image signal noise ratio (SNR) between different aspects images also need to be considered, so a ViSAR generation method is proposed to solve the above problems. Finally, the results of ViSAR in THz and Ku band demonstrate the effectiveness and practicability of the proposed method.

Wide-angle staring synthetic aperture radar ground moving target indication (WasSAR-GMTI) has been widely recognized for its long-term observation capabilities of fixed areas and its achievement in moving target tracking. Recently, the research on moving target trajectory reconstruction has also raised interest. However, the neglect of height-dimensional information makes it difficult to apply in the scene with terrain undulation. In this paper, a three-dimensions (3-D) trajectory reconstruction method with L-antenna which combines interferometry SAR (InSAR) and GMTI technique is proposed. Meanwhile, it’s the first time that L-antenna is applied in 3-D geo-location of moving target. Firstly, the echo is segmented into several sub-apertures and the lever arm compensation and back projection (BP) imaging are required to register the multi-channel images. Secondly, the along-track multi-channel is processed which contains clutter rejection and radial velocity estimation. Thirdly, the cross-track interferometric phase extraction is proposed and 3-D geo-location of moving target is estimated. Apart from extracting height-dimensional information from interferometric phase directly, a method based on digital elevation model (DEM) is also proposed. And the comparison of the two methods is given in this paper. The processing results of real data have confirmed the efficacy and practicality of the proposed algorithm.