Yunkai Deng

Processing the Azimuth-Variant Bistatic SAR Data by Using Monostatic Imaging Algorithms Based on Two-Dimensional Principle of Stationary Phase

This paper presents a new bistatic point target reference spectrum. It is derived by using the 2-D principle of stationary phase which is first applied in the synthetic aperture radar (SAR) community. The spectrum contains two hyperbolic range-azimuth coupling terms and thus is very similar to the monostatic spectrum. It shows the characteristic of the conventional monostatic SAR besides an additional azimuth scaling term. Therefore, it makes the common Doppler-based monostatic processing algorithms readily suitable to handle the Bistatic SAR (BiSAR) data in the moderate-squint azimuth-variant configurations with two moving platforms. Based on the spectrum, two Doppler-based monostatic imaging algorithms [i.e., range-Doppler algorithm (RDA) and chirp-scaling algorithm (CSA)] are readily implemented to deal with the moderate-squint azimuth-variant BiSAR data. Compared to the processing procedure for the monostatic SAR, the RDA and CSA for the BiSAR need only the adjustment of Doppler parameters. Finally, the potential and limitation of the spectrum are analyzed, and the real raw data in the spaceborne/airborne configurations are used to validate the proposed spectrum and processing methods.

A New CFAR Ship Detection Algorithm Based on 2-D Joint Log-Normal Distribution in SAR Images

The characteristic difference between targets and clutter is analyzed. Considering the ship targets gray intensity distribution and its shape difference compared to the clutter, in this letter, a new algorithm is presented based on correlation. The algorithm utilizes the strong gray intensity correlation in the ship target; also, the joint gray intensity distribution using 2-D joint log-normal distribution of a pixel with neighboring pixels in the clutter is modeled, which can be used for correlation-based joint constant false alarm rate detection. Using this algorithm, the false alarms caused by speckle and local background nonhomogeneity can be greatly reduced. The detection performance is much better.

Squint Spotlight SAR Raw Signal Simulation in the Frequency Domain Using Optical Principles

Synthetic aperture radar (SAR) distributed target scene raw signal simulation is an important tool for the study and test of SAR systems and processing algorithms, mission planning, and inversion algorithm design. In this paper, the squint spotlight SAR scene model is evaluated to achieve spotlight SAR raw signals in the 2-D frequency domain and the precision of the model is analyzed. It is known that the range migration phenomenon in the time domain is explained as the coupling between the range and azimuth in the 2-D frequency domain. To realize the coupling relation in the 2-D frequency, interpolation may be needed. However, interpolation is a time-consuming manipulation. For efficiency, some signal processing methods are employed to couple the range and azimuth frequencies. Those tricks are derived from some optical principles, which give us some novel thoughts. Therefore, the efficiency of the simulator is highly improved, which facilitates its application to the verification and test of the real-time processor.

An Efficient Approach With Scaling Factors for TOPS-Mode SAR Data Focusing

The Terrain Observation by Progressive Scans (TOPS) mode is a novel spaceborne imaging mode which can be used to obtain wide-swath coverage and overcome major drawbacks in conventional ScanSAR. An efficient full-aperture imaging approach, which takes advantage of the two-step focusing technique and the azimuth baseband scaling operation, is presented for processing the TOPS-mode synthetic aperture radar (SAR) data. First, the proposed two-step focusing technique for spotlight and sliding spotlight SAR data focusing is adopted to resolve the aliased Doppler spectrum. Afterward, the following extended chirp scaling processing procedure with azimuth scaling factors is used to implement the residual TOPS raw-data focusing. Since the use of subapertures is avoided and only a limited azimuth-data extension is required, this algorithm is highly efficient. Simulation results validate the proposed imaging approach.

MULTI-CHANNEL SPCMB-TOPS SAR FOR HIGH- RESOLUTION WIDE-SWATH IMAGING

To improve the impaired azimuth resolution of the novel Terrain Observation by Progressive Scans (TOPS) mode, a new multi- channel single phase center multiple beam (SPCMB) TOPS mode is proposed in this paper for high-resolution wide-swath (HRWS) imaging. However, the progressive azimuth beam scanning leads to the Doppler spectrum aliasing and both beam center time and Doppler centroid varying with the targets azimuth location. Challenges may arise for processing the SPCMB-TOPS SAR data from these problems. In this paper, an e-cient full aperture imaging approach is proposed to process the raw data. The sketch of the proposed imaging approach is described in detail. Simulation results of point targets validate the proposed imaging approach.

Ground Moving Target Extraction in a Multichannel Wide-Area Surveillance SAR/GMTI System via the Relaxed PCP

This letter presents a novel approach for extracting moving targets in a multichannel wide-area surveillance radar system. In the algorithm, after proper preprocessing and matrix combination, the combined matrix of radar echoes can be regarded as the superposition of three matrices, namely, a low-rank matrix of ground clutter, a sparse matrix of moving targets, and an entry-wise matrix of noise component. Then, the recently proposed relaxed version of principal component pursuit is used to realize ground clutter (low-rank matrix) and moving target (sparse matrix) separation under the influence of entry-wise noise. Both simulation and real data processing results are provided to demonstrate the effectiveness of the proposed method. In addition, the results show the advantage of the proposed method in a nonhomogeneous environment when compared with a reduced-dimension space-time adaptive processing method.

Fast Backprojection Algorithm for Bistatic SAR Imaging

In this letter, a fast backprojection algorithm (FBPA) is proposed for bistatic synthetic aperture radar imaging. For range compression, the signal recorded by the synchronization channel of the receiver on the ground is used as a matched filter to compress the echo signal. This method can reduce the requirements of satellite-orbit measurement and synchronization precision. For azimuth compression, a secondary phase correction is implemented to reduce the effect caused by the approximation involved in the FBPA. The computational complexity of the proposed algorithm is O(N2.5). The proposed algorithm is applied in a graphics processing unit and verified by simulation and real raw data.

Internal Calibration for Stepped-Frequency Chirp SAR Imaging

For synthetic aperture radar imaging, stepped-frequency chirp signals are widely used to obtain high range resolution. One advantage of the approach is the reduction of the instantaneous bandwidth and sampling rate requirements of the radar system. To reconstruct the spectrum of a wideband signal, the amplitude and phase discontinuity between contiguous pulses should be removed. Otherwise, the discontinuity will defocus the range profile and degrade the range resolution. In this letter, a detailed internal calibration technique combined with stepped-frequency mode is proposed to eliminate the discontinuity and thus improve the focusing quality of the final image. The simulation and real raw data experiments are performed to validate the proposed method.

Arc FMCW SAR and Applications in Ground Monitoring

As a novel mode of ground-based synthetic aperture radar (GB-SAR), Arc frequency-modulated continuous wave (FMCW) SAR is rarely discussed in the literature up to now. Compared with the conventional rail GB-SAR system, the synthetic aperture is formed by the rotation of antennas, which can scan a wide azimuth extent. Due to its convenience and potential in SAR applications, the Institute of Electronics, Chinese Academy Sciences, carried out a series of Arc FMCW SAR experiments in March 2013, and a lot of results were obtained. In this paper, we discuss the signal processing of Arc FMCW SAR and its first results in change detection and interferometric SAR. The components of the Arc FMCW SAR system are first described, and then, we focus on its signal processing, where the signal model and its properties are investigated; two focusing algorithms are developed for different purposes. The effectiveness of the algorithms is validated by both simulation and real data experiments. We also exhibit the applications of Arc FMCW SAR in landslide detection and digital-elevation-model extraction for the first time. Results show its huge potential in ground-based applications.

Multichannel InSAR DEM Reconstruction Through Improved Closed-Form Robust Chinese Remainder Theorem

Interferometric synthetic aperture radar (InSAR) multichannel system, which produces more than one interferogram in a multifrequency or multibaseline configuration, allows us to reconstruct highly sloped and discontinuous terrain height profiles. In this letter, a novel method based on a closed-form robust Chinese remainder theorem (CRT) is presented to solve the height reconstruction problem. Proper reference remainder selection and remainder differential process, which do not exist in the traditional CRT, are adopted to improve the robustness of the height reconstruction. We also modify the method by exploiting statistical characteristics of interferometric phase and the combined information of InSAR interferograms. Moreover, a special weighted mean filtering method is adopted to get a better result. Experimental results prove the effectiveness of the method.