Bistatic Inverse Synthetic Aperture Radar Research Articles

Bistatic ISAR distortion and defocusing analysis

Bistatic inverse synthetic aperture radar (ISAR) is an efficient geometric configuration of ISAR to image targets traveling along radar transmitter's line of sight, but it has the problem of defocusing and distortion because of the time-varying bistatic angle. In this paper, we derive the defocusing term and the distortion term by expanding the bistatic angle using first-order Taylor expansion. In addition, necessary constraints to neglect the defocusing term are provided via point spread function analysis, and a novel method to eliminate distortion based on linked scatterers is proposed. Simulation results validate our theoretical analysis and show the effectiveness of our method.

Defocusing and distortion elimination for shipborne bistatic ISAR

ABSTRACTShipborne bistatic inverse synthetic aperture radar (ISAR), with a stationary and visible transmitter on land and a mobile and stealthy receiver on a ship with complex 3-D rotations is a strategic asset which can provide complementary information to monostatic ISAR. However, it must first overcome the serious problems of defocusing and distortion due to the time-varying bistatic angle. In this letter, an improved cubic chirplet decomposition method is proposed to solve the defocusing problem. By decomposing the ISAR echo into cubic chirplet atoms and estimating the parameters for each term, higher-order defocusing terms can be eliminated. Moreover, a novel method based on linked scatterers is put forward to solve the distortion problem. The method utilizes ‘linked scatterers’ from monostatic ISAR image to calculate and compensate the distortion angle. The effectiveness of the proposed methods is verified by the simulation results.

Analysis of synchronization errors for InISAR on separated platforms

Bistatic inverse synthetic aperture radar (BiISAR) imaging and interferometric inverse synthetic aperture radar (InISAR) imaging can provide complementary information to monostatic inverse synthetic aperture radar (MoISAR) imaging. Time synchronization is a requirement for both systems. This paper focuses on the problem of the time synchronization in the BiISAR and InISAR imaging with a polynomial time synchronization error model (PTSEM) in theory. The effects of the time synchronization errors to the range and azimuth compression with the synchronization errors are analyzed in detail. A phase error model transferred from the synchronization errors to the interferometric error is established. A simulation displays the results of the analysis.

시간-주파수 변환에 요동보상을 적용한 UWB 레이다 바이스테틱 ISAR 이미징

본 논문에서는 시간-주파수 변환에 요동보상을 적용한 UWB 레이다 Bistatic ISAR (Bistatic Inverse Synthetic Aperture Radar: B-ISAR) 이미징에 적용하여 레이다 이미징의 선명도와 품질을 개선하였다. UWB 레이다를 사용하여 제안하는 시간-주파수 알고리즘을 검증하였으며, 이를 위하여 B-ISAR 알고리즘 절차, 시간-주파수 변환과 요동보상 개선 등 필요한 이론적 근거를 제시하였다. B-ISAR 이미징 알고리즘으로 이미지를 생성하였으며, UWB 바이스테틱 ISAR 이미징 생성시 요동보상을 적용한 시간-주파수 변환 기법인 STFT(Short-Time Fourier Transform), GWT(Gabor Wavelet Transform), WVD(Wigner-Ville distribution) 방식을 차례대로 구현하였다. 그리고 STFT, GWT와 WVD 알고리즘을 이용하여 B-ISAR 이미징 알고리즘의 성능을 비교하였으며, 그 결과 WVD가 다른 방식들에 비하여 영상이 선명하고, 퍼짐 현상이 줄어듦을 알 수 있었다. In this paper, we improved the clarity and quality of the radar imaging by applying motion compensation for time-frequency transform in B-ISAR imaging. The proposed motion compensation algorithm using UWB radar is verified. B-ISAR algorithm procedure and time-frequency transform for improved motion compensation are provided for theoretical ground. The image was created by a UWB Radar B-ISAR imaging algorithm method. Also, creating a B-ISAR imaging algorithm for motion compensation of time-frequency transformation method was used. The B-ISAR Imaging algorithm is implemented using STFT(Short-Time Fourier Transform), GWT(Gabor Wavelet Transform), and WVD(Wigner-Ville Distribution) approaches. The performance of STFT is compared with the GWT and WVD algorithms. It is found that the WVD image shows more clarity and decreased spread phenomenon than other methods.

High-Resolution Bistatic ISAR Image Formation for High-Speed and Complex-Motion Targets

The existing bistatic inverse synthetic aperture radar (Bi-ISAR) imaging methods usually uses a “stop-and-go” assumption where the target can be considered not in motion (stop condition) during the fast-time and in motion (go condition) during the slow time. However, for the high-speed target, this assumption is violated; furthermore, the conventional compression via Fourier transform is also invalid due to the quadratic phase term induced by the high-speed motion. In this case, a range compression method using the fractional Fourier transform (FrFT) based on minimum entropy criterion is presented to obtain high-resolution one-dimensional (1-D) range profile. Moreover, to achieve azimuth focusing for the complex-motion target, a new method of imaging time selection based on frequency smooth degree (FSD) is proposed. Simulated and real data are provided to verify the effectiveness of the proposed method.

Compressive sensing–based algorithm for passive bistatic ISAR with DVB-T signals

Inverse synthetic aperture radar (ISAR) images can be obtained using digital video broadcasting–terrestrial (DVB-T)–based passive radars. However, television broadcast–transmitted signals offer poor range resolution for imaging purposes, because they have a narrower bandwidth with respect to those transmitted by a dedicated ISAR system. To reach finer range resolutions, signals composed of multiple DVB-T channels are required. Problems arise, however, because DVB-T channels are typically widely separated in the frequency domain. The gaps between channels produce high grating lobes in the image domain when Fourier-based algorithms are used to form the ISAR image. In this paper, compressive sensing theory is investigated to address this problem because of its ability to reconstruct sparse signals by using incomplete measures. By solving an optimization problem under the constraint of signal sparsity, passive ISAR images can be obtained with strongly reduced grating lobes. Both simulation and experimental results are shown to demonstrate the validity of the proposed approach.

High-Resolution Bistatic ISAR Imaging Based on Two-Dimensional Compressed Sensing

The theory of compressed sensing (CS) states that an unknown sparse signal can be accurately recovered from a limited number of measurements by solving a sparsity-constrained optimization problem. In this paper, we present a new framework of high-resolution bistatic inverse synthetic aperture radar (Bi-ISAR) imaging based on CS. A phase-preserved CS approach for high-range resolution imaging is proposed. The phase of a Bi-ISAR signal can be extracted by constructing a phase-preserved Fourier basis, which is crucial to azimuth processing of Bi-ISAR imaging. After performing CS reconstruction in range, we present an improved version of CS-based cross-range imaging by combining modified Fourier basis and weighting with CS optimization. Simulated data are used to test the robustness of the Bi-ISAR imaging framework with two-dimensional (2-D) CS method. The results show that the framework is capable of accurate reconstruction of Bi-ISAR image in both range and cross-range.

Bistatic three-dimensional interferometric ISAR image reconstruction

A three-dimensional (3D) bistatic inverse synthetic aperture radar (ISAR) imaging method is proposed in this paper. The proposed method makes use of interferometry and technically speaking, produces a 3D target reconstruction by estimating a scattering center position in 3D Cartesian space. The proposed method makes use of a combined ISAR/interferometry technique that also allows the ISAR image plane to orientation to be estimated. Cross- or L-shaped antenna configurations are discussed, and the effects of the baseline length along the horizontal and vertical direction on the scatterer’s position estimation are analyzed in detail. Finally, numerical simulations are used to evaluate the proposed method’s performance.

Research on spatial-variant property of bistatic ISAR imaging plane of space target**Project supported by the National Natural Science Foundation of China (Grant No. 61401024), the Shanghai Aerospace Science and Technology Innovation Foundation, China (Grant No. SAST201240), and the Basic Research Foundation of Beijing Institute of Technology (Grant No. 20140542001).

The imaging plane of inverse synthetic aperture radar (ISAR) is the projection plane of the target. When taking an image using the range-Doppler theory, the imaging plane may have a spatial-variant property, which causes the change of scatter’s projection position and results in migration through resolution cells. In this study, we focus on the spatial-variant property of the imaging plane of a three-axis-stabilized space target. The innovative contributions are as follows. 1) The target motion model in orbit is provided based on a two-body model. 2) The instantaneous imaging plane is determined by the method of vector analysis. 3) Three Euler angles are introduced to describe the spatial-variant property of the imaging plane, and the image quality is analyzed. The simulation results confirm the analysis of the spatial-variant property. The research in this study is significant for the selection of the imaging segment, and provides the evidence for the following data processing and compensation algorithm.

Three-dimensional bistatic interferometric ISAR imaging

An approach based on interferometry technique is proposed for three-dimensional( 3D) bistatic inverse synthetic aperture radar( ISAR) imaging. It is converted to a monostatic problem by using the theory that a bistatic radar equals a monostatic radar located on the bisector of bistatic angle. Then,interferometric phases extracted from a pair of cross shaped antennas are used to estimate the height and associated rotational velocity.Finally,numerical simulations are provided to evaluate this method.

Two-Dimensional Imaging Algorithm Based on Linear Prognosis for Space Target in Bistatic ISAR System

In bistatic inverse synthetic aperture radar (Bi-ISAR) system, its image resolution is lower than monostatic ISAR system. In order to solve this problem, the linear prognosis algorithm is adopted in the imaging process and the imaging algorithm based on linear prognosis is proposed. Space target Bi-ISAR imaging is taken as example in the research. The one-dimensional range profile is created through pulse compression method. Before the azimuth compression, burg entropy maximum algorithm in Levions recursive method is used to estimate the prognosis coefficients and the azimuth echo data. Then Fourier transformation is used to compress the azimuth data in order to get the high resolution azimuth image. This imaging method can obtain the two-dimensional image with the resolution equal to the monostatic ISAR or even higher than it. Simulation experiments have verified the effectiveness and availability of the algorithm.

Theoretical foundation of passive bistatic ISAR imaging

Passive bistatic inverse synthetic aperture radar (PB-ISAR) has been recently introduced to add an important capability to passive coherent location (PCL) systems. Although evidence of such capability has been provided, a theoretical background that supports such findings is needed to fully comprehend PB-ISAR imaging. This paper provides a full theoretical basis for PB-ISAR including a performance analysis in terms of spatial resolution. Examples with real data are also provided as case studies.

A Novel Model for Three-Dimensional Imaging Using Interferometric ISAR in Any Curved Target Flight Path

Using a second receiver antenna close to the main transceiver antenna of inverse synthetic aperture radar (ISAR), it is possible to find 3-D positions of target scattering points. Such system is called bistatic, monopulse, or interferometric ISAR (InISAR). In the conventional model of ISAR, the unknown flying object should have a linear trajectory, and only small deviations from this trajectory can be compensated. Target motions which are highly nonlinear or curvy cannot be used in the conventional model. In this paper, we propose a new model for InISAR to process all collected data from the target, regardless of the form of the flight path. More accuracy is achieved for 3-D positioning of the target scattering points by this model because all parts of the flight path contribute in it. We will show the effectiveness of the proposed model in a nonlinear flight path by simulation.

바이스태틱 ISAR 영상 생성 시뮬레이션

Abstract This paper introduces a bistatic ISAR imaging technique. In bistatic geometry, the transmitter and receiver are placed in different locations. The monostatic ISAR is inadequate not only for obtaining images on targets approaching along the radar’s line of sight, but also for stealth targets. In this paper, geometry, signal modeling as well as bistatic Doppler for bistatic ISAR are introduced to address these problems. Simulations results show bistatic ISAR images as well as monostatic ISAR images against target’s moving scenarios, and analyze their differences for each scenario.Key words: Bistatic ISAR Image, Bistatic Radar, Bistatic Doppler `%)*abcLd*Le%N=f) /IR /0ghij%kablm, .nopq.r stuL#e^vwueL(Department of Electrical Engineering, Pohang University of Science and Technology) *d*Le%N(Agency for Defense Development)Manuscript received October 7, 2013 ; Revised February 5, 2014 ; Accepted February 10, 2014. (ID No. 20131007-089)Corresponding Author: Kyung-Tae Kim (e-mail: kkt@postech.ac.kr)

On deception jamming for countering bistatic ISAR based on sub‐Nyquist sampling

Bistatic inverse synthetic aperture radar (ISAR) operates with spatially separated transmitting and receiving antennas. This study presents a method capable of generating deceptive images from a series of intercepted bistatic ISAR chirp pulses. It is demonstrated that deceptive false-target images will be induced by the under-sampled pulses which are retransmitted to a moving target and scattered by it under the principles of bistatic ISAR configuration. Additionally, the jamming idea is proved to be applicable based on the characteristics of the false-target images and the requirement of jamming power. A scattering model of Yak-42 plane with 330 point scatterers is adopted to verify the effectiveness of the jamming idea.

Correction of migration through resolution cell in bistatic inverse synthetic aperture radar in the presence of time-varying bistatic angle

When the size of target or the rotation angle is big, migration through resolution cell may occur in the bistatic inverse synthetic aperture radar (ISAR), which will affect the imaging quality. Aiming at the problem of migration through resolution cell of bistatic ISAR in the presence of time-varying bistatic angle, a correction algorithm is proposed in this paper. Firstly, the echo model of bistatic ISAR is built, and the mechanism of migration through resolution cell is analyzed. Migration through range cell may be corrected through the generalized Keystone transformation, and the effect of non-uniform rotation is eliminated at the same time. Then the rotating center is estimated according to the maximum criterion of image contrast, and the range bin is scaled absolutely. A phase compensation term is constructed and the correction of migration through Doppler cell is finished. Finally, the simulations are carried out and the results show that the method proposed in this paper can solve the problem of migration through resolution cell and improve the image quality.

A New Methodology for Measuring the Bistatic Ground Scattering Coefficient. Comparisons With the AIEM at Large Bistatic Angles

In this letter, we present a new methodology for measuring the bistatic ground scattering coefficient σ0 at large bistatic angles and in the near field of a rough surface. To filter out unwanted radar returns, out-gating from bistatic inverse synthetic aperture radar (ISAR) imaging is performed for the area of interest. Comparisons are made with a near-field compensated advanced integral equation method model.

3D Imaging of Bistatic Inverse Synthetic Aperture Radar Based on the Factorization Method

Based on the geometrical projection of 3D scattering centers on the line of radar sight, a new method of bistatic inverse synthetic aperture radar 3D Imaging is proposed. In the method, Range-Doppler algorithm gives a sequence of 2D images of target during its motion, and 3D reconstruction of target geometry is completed by the factorization method. We analyzed the theory of Bi-ISAR 3D imaging, deduced the process of the factorization method, and introduced the hierarchical reconstruction model. The simulation verified the validity of the paper.

Developments in target micro-Doppler signatures analysis: radar imaging, ultrasound and through-the-wall radar

Target motions, other than the main bulk translation of the target, induce Doppler modulations around the main Doppler shift that form what is commonly called a target micro-Doppler signature. Radar micro-Doppler signatures are generally both target and action specific and hence can be used to classify and recognise targets as well as to identify possible threats. In recent years, research into the use of micro-Doppler signatures for target classification to address many defence and security challenges has been of increasing interest. In this article, we present a review of the work published in the last 10 years on emerging applications of radar target analysis using micro-Doppler signatures. Specifically we review micro-Doppler target signatures in bistatic SAR and ISAR, through-the-wall radar and ultrasound radar. This article has been compiled to provide radar practitioners with a unique reference source covering the latest developments in micro-Doppler analysis, extraction and mitigation techniques. The article shows that this research area is highly active and fast moving and demonstrates that micro-Doppler techniques can provide important solutions to many radar target classification challenges.

Bistatic ISAR Imaging Incorporating Interferometric 3-D Imaging Technique

Bistatic inverse synthetic aperture radar (BiISAR) imaging provides complementary information to monostatic ISAR imaging. A suggestion that the conventional bistatic ISAR can be replaced by an equivalent monostatic radar is shown to be inadequate in this paper. We prove that the BiISAR image is a sheared version of the projection of the target on the range-Doppler plane. A bistatic interferometric radar configuration is proposed to correct this distortion and to form 3-D image. Simulation results have validated our analysis and shown the viability of the proposed 3-D imaging algorithm.