Showing papers by "Mengdao Xing published in 2009"

Motion Compensation for UAV SAR Based on Raw Radar Data

Abstract: Unmanned aerial vehicle (UAV) synthetic aperture radar (SAR) is very important for battlefield awareness. For SAR systems mounted on a UAV, the motion errors can be considerably high due to atmospheric turbulence and aircraft properties, such as its small size, which makes motion compensation (MOCO) in UAV SAR more urgent than other SAR systems. In this paper, based on 3-D motion error analysis, a novel 3-D MOCO method is proposed. The main idea is to extract necessary motion parameters, i.e., forward velocity and displacement in line-of-sight direction, from radar raw data, based on an instantaneous Doppler rate estimate. Experimental results show that the proposed method is suitable for low- or medium-altitude UAV SAR systems equipped with a low-accuracy inertial navigation system.

Achieving Higher Resolution ISAR Imaging With Limited Pulses via Compressed Sampling

Abstract: Recent theory of compressed sampling (CS) suggests that exact recovery of an unknown sparse signal with overwhelming probability can be achieved from very limited number of samples. In this letter, we adapt this idea and present a framework of high-resolution inverse synthetic aperture radar imaging with limited measured data. During the framework, we mathematically convert the imaging into a problem of signal reconstruction with orthogonal basis; hence, a conceptive upper bound of the cross-range resolution is presented based on the CS theory. Real data results show that the CS imaging approach outperforms the conventional range-Doppler one in resolution.

New ISAR imaging algorithm based on modified Wigner–Ville distribution

Abstract: Inverse synthetic aperture radar (ISAR) imaging of air, space or ship targets with complex motion has attracted the attention of many researchers in the past decade. Complex motion of targets induce cross-range scatterer-variant quadratic phase terms, which will degrade the cross-range resolution and affect focusing quality. A new algorithm is proposed for the ISAR imaging of complex moving targets. First, conventional range alignment, phase compensation and range compression are performed over the raw phase history data such that each range bin can be modelled as the sum of several linear frequency modulation or chirp signals. Secondly, a modified-Wigner-Ville distribution (referred to as M-WVD) approach is proposed, which is based on a scale transform in the time-frequency distribution plane and can effectively suppress the troublesome cross-term interference associated with WVD via coherent integration. Finally, the azimuth ISAR image can be obtained via a simple maximisation projection from the two-dimensional accumulated plot to the azimuth dimension. Compared with existing WVD-based ISAR imaging algorithms, the proposed method has the following features: better cross-term interference reduction achieved at no resolution loss, computationally more efficient with no expensive two-dimensional parameter search, and higher signal processing gain because of coherent integration during the whole imaging time. Both numerical and experimental results are provided to demonstrate the performance of the proposed method.

Narrow-Band Interference Suppression for SAR Based on Complex Empirical Mode Decomposition

Abstract: Narrow-band interference (NBI) is a common interference source in synthetic aperture radar (SAR) imaging. Its existence will degrade the imaging quality greatly. Based on detailed analysis on the characteristics of NBI, this letter proposes a new NBI suppression algorithm using the complex empirical mode decomposition (CEMD) method. In this algorithm, echoes that include NBI are recognized in the time domain first. Then, these echoes are decomposed into a number of intrinsic mode functions (IMFs) via the CEMD. After that, IMFs that correspond to NBI are subtracted from the echoes by thresholding. Finally, well-focused SAR imagery can be obtained from the separated target echoes using traditional SAR imaging algorithms. The effective data loss in this algorithm is smaller than other NBI suppression approaches. In addition, this algorithm is robust to time-varying NBI. Imaging results of measured data have proved the validity of this algorithm.

High-Resolution Three-Dimensional Imaging of Spinning Space Debris

Abstract: Since space debris could post a significant threat to orbiting objects around the Earth, their reorganization, measurement, and catalogue are of great importance. This paper establishes a 3-D inverse synthetic aperture radar (ISAR) imaging geometry and signal model for space debris. Then, a 3-D imaging algorithm is proposed to realize coherent imaging in the range-slow-time domain. This algorithm is based on the complex-valued back-projection transform according to the spinning nature of space debris. The simulation results for both point scattering and continuous targets have proved the validity of the proposed algorithm.

Unambiguous Reconstruction and High-Resolution Imaging for Multiple-Channel SAR and Airborne Experiment Results

Abstract: Azimuth ambiguity occurs in synthetic aperture radar (SAR) systems due to the well-known constraint of minimum antenna area, particularly at high resolutions and wide swaths. A space time domain method can be utilized to remove this ambiguity if the multiple-channel data are available. In this letter, a modified approach is presented to determine the filter weight vectors. This approach was successfully applied to the real data, which were collected by an experimental airborne multiple-channel SAR system. The channel imbalance and the error in antenna phase center position are analyzed in detail.

A Matched-Filter-Bank-Based 3-D Imaging Algorithm for Rapidly Spinning Targets

Abstract: For rapidly spinning targets, such as the rotating ground radar antenna, helicopter blades, spinning space debris, etc., the scatterers on the target may rotate for several periods in the observation time. Since the range and Doppler information of these scatterers are no longer constant, the conventional range-Doppler-based imaging algorithms are invalid. Meanwhile, 3-D imaging is necessary to obtain additional information for the spinning target. However, the available interferometric inverse synthetic radar (ISAR) and snapshot 3-D imaging algorithms do not work well since they require low target spinning speed. In this paper, a matched-filter-bank-based 3-D imaging algorithm for rapidly spinning targets is proposed, based on target motion features. This algorithm utilizes the rapidly rotating turntable model of the ISAR target instead of the slow rotating one. First, 2-D image slices of the target are obtained from the output of the matched filter bank by changing matching parameters. Then, a series of 2-D image slices are combined to form the 3-D target image. Since this algorithm applies to the monostatic radar system, it is easy to implement in practical applications. Both the theoretical derivation and the simulation results have proved the validity of the proposed algorithm.

Two-dimensional pulse-to-pulse canceller of ground clutter in airborne radar

Abstract: It is well known that in the airborne radar, the location of the ground clutter spectrum in the angle-Doppler space is dependent mainly on the platform velocity and radar parameters. The authors propose a two-dimensional pulse-to-pulse canceller (TDPC) that can make full use of such prior information. The more detailed formulations of the ground clutter model and the signal model are given in a matrix-vector form. The least-squares-typical cost function associated with the filter coefficient matrix of the TDPC is established on the basis of the ground clutter model and the signal model. Like the classical displaced phase centre antenna (DPCA) processing, the proposed TDPC is also a spatial-temporal suppressor of ground clutter and can decrease the ground clutter signals, even though the DPCA condition is not satisfied. The proposed TDPC can also be used as an efficient pre-filtering tool before the conventional moving target indication (MTI) processing and the classical adaptive processing. Moreover, if only the TDPC plus the conventional MTI is used, it takes less computational time than the adaptive canceller. Experimental results show that the proposed TDPC has the satisfactory ground clutter suppression capability by using both simulated data and measured data.

Azimuth-invariant bistatic multichannel synthetic aperture radar for moving target detection and location

Abstract: Ground moving target indication (GMTI) is one of the most important applications of the bistatic synthetic aperture radar (SAR) system as well as the monostatic system. An algorithm for moving target detection and location is presented with an azimuth-invariant bistatic multichannel SAR, which consists of one transmitter (channel) and multireceivers (multichannel). The algorithm is based on the discussion of the particularities of the bistatic SAR configuration including coherence improvement and clutter characteristics. Then, the corresponding compensating methods including two-dimensional range-azimuth prefiltering and bistatic differential range correction are proposed to solve these particularities. It is shown that using the compensating methods, the stationary clutter can be suppressed and the moving parameters of ground targets can be estimated accurately. Finally, simulation results demonstrate the effectiveness of the proposed algorithm.

Two-Dimensional Spectrum Matched Filter Banks for High-Speed Spinning-Target Three-Dimensional ISAR Imaging

Abstract: In this letter, a 3-D inversed synthetic aperture radar imaging algorithm for targets in high-speed spinning is proposed based on 2-D spectrum matched filter (MF) banks. Each spectrum MF bank yields a focused slice for its corresponding scatterers. By extracting the spatial parameters from all slices, the 3-D image of the target can be constructed. Numeric simulation confirms the validity of the algorithm.

SAR imaging of multiple ships based on compressed sensing

Abstract: Recent theory of Compressed Sensing (CS) gives us a novel version that an unknown sparse signal can be exact recovery with overwhelming probability beyond Nyquist sampling constraints. In this paper, we adapt this idea and present a framework of high-resolution synthetic aperture radar (SAR) imaging with multiple ships. Under the framework, we convert the multiple ships imaging into a problem of sparse signal reconstruction with certain orthogonal basis, hence the sparse reconstruction of CS can be fulfilled and a theoretical upper bound of the cross-range resolution is presented. Real data results verify the effectiveness of the CS imaging framework.

Research on indoor experimentation of range SAL imaging system

Abstract: By means of advantages of both SAR and lidar, the combination of the techniques of (inverse) synthetic aperture and lidar makes it possible to obtain high resolution 2-D image. In this paper, an indoor experimental system of inverse synthetic aperture lidar imaging is given and a processing approach is presented. The given system is in the mode of lidar system with separated receiver and transmitter, which can effectively eliminate the jamming from the lens or/and the intersection between two optic fibers. Based on the reference channel techniques, a method for the compensation of nonlinear frequency in the time domain is presented, which can solve the problem of nonlinear frequency efficiently. Then, with the mature inverse synthetic aperture algorithm, an image of inverse synthetic aperture lidar can be obtained, which is the first attempt in China. Finally, experimental results confirm the validity of the presented method and the feasibility of the experimental system.

Experimental results on ISAR imaging with stepped-frequency waveforms

Abstract: A simple and successful processing for the bandwidth synthetic of stepped-frequency waveforms (SFWs) is presented. The high range resolution is obtained by combining the sub-pulses of SFWs in the frequency domain. The overlapping bandwidth of the two adjacent sub-pulses is used to estimate phase errors. Also the usual motion compensation approach is avoided if the band coherent processing is used. Experimental results of the ship target are shown.

High-speed ground moving target detection research using triangular modulation FMCW

Abstract: The frequency modulated continuous wave (FMCW) radar has the characteristics of low probability of interception, good hidden property and the ability to counter anti-radiation missiles. This paper proposes a new method for high-speed ground moving target detection (GMTD) using triangular modulation FMCW. According to the characteristic of the opposite range shift induced by the upslope and downslope modulation FMCW, the upslope and downslope are imaged, respectively. After compensation of continuous motion of the platform and time difference between upslope and downslope signals for imaging, the moving target can be detected through displaced phase center antenna (DPCA) technology. When the moving target is detected, the moving target image is extracted, and correlation processing is used to obtain the range shift, which can be used to estimate the target radial velocity, and further to find the real position of the target. The effectiveness of this method is verified by the result of computer simulation.

Micro-Doppler analysis and imaging of air-planes with rotating parts

Abstract: In ISAR imaging of air-planes with rotating parts, the micro-Doppler phenomenon induced by the rotors will generate side-bands about the rigid body image This paper derives the imaging model and analyzes the micro-Doppler of rotors Then, a method for micro-Doppler separation based on low chirp rate matching is proposed Meanwhile, an algorithm for scaling the 2D imaging of rigid body is presented, based on the complex-valued back-projection algorithm Similarly, ISAR imaging of the rotating rotors can be obtained through the same algorithm Finally, images from the rigid body and the rotating rotors are merged together to obtain a full image of the air-plane The validity of the proposed algorithms has been proved by simulations

Wide swath, high range resolution imaging with MIMO-SAR

Abstract: The paper describes a novel approach combining space filtering with bandwidth synthesis to achieve wide swath and high range resolution, Firstly, Low PRF is adopted to achieve unambiguous wide swath; then space filters is used to remove azimuth ambiguity; finally sub-band signals are combined into a wider band signal to achieve high range resolution. Simulation results are provided to show the validity of the proposed method. (6 pages)

Unparallel trajectory bistatic spotlight SAR imaging

Abstract: A new approach for unparallel trajectory bistatic spotlight SAR imaging is proposed. The approach utilizes the concept of instantaneous Doppler wavenumber and introduces two variants, the sum-range and subtraction-range, to develop the 2D frequency analytical formula. Based on the assumption of plane wavefront, the transmitting and receiving Doppler are separated and formulated via series reversion. And frequency scaling is applied to focus image. The algorithm is with high computational efficiency, and provides well focus for limited scene imaging. Simulation result confirms the validity of the approach.

Coherence-Improving Algorithm for Image Pairs of Bistatic SARs With Nonparallel Trajectories

Abstract: Ground moving target indication (GMTI) is one of the most important applications in a general bistatic synthetic aperture radar (SAR) system, where the transmitter and receiver move along nonparallel trajectories with different velocities. In order to improve the capability of clutter cancellation in bistatic SAR/GMTI processing, the coherence between two echoes collected by two receivers is investigated, and the full-coherence conditions are derived. A new coherence-improving algorithm for general bistatic SAR complex image pairs is proposed, which can be realized in the following steps: 2-D range azimuth prefiltering processing, relative geometric deformation correction, and image registration. An approximate implementation of 2-D prefiltering and the corresponding prefilter parameter analysis are also given. Last, two numerical experiment results are given to demonstrate the effectiveness of the proposed algorithm.

Detection, parameter estimation and imaging of maneuvering target in wide-band signal

Abstract: The signal-to-noise ratio may be increased by the cross-range coherence integration so as to detect the moving target in low signal-to-noise ratio (SNR) condition But, the radial velocity, acceleration and the change of acceleration due to the maneuvering motion of target may induce serious range migration and cross-range high-order phase terms leading to the unfocused cross-range image, the reduction of signal-noise ratio and the invalidation of target detection Therefore, in order to solve these problems, this paper proposes a new method based on the adjacent correlation and scale transform methods for detection, parameters estimation and imaging of maneuvering targets in wide-band signal This method can align the range and remove the cross-range high-order phase terms induced by the radial motion of target, enabling us to detect the target and estimate its moving parameters better Finally, the simulated target is used to confirm that the method proposed by this paper can perfectly detect the maneuvering target in low signal-to-noise ratio condition, estimate its motion parameters and obtain an ISAR image of target

Study on synthetic aperture imaging lidar based on a laboratory-scale sliding guide system

Abstract: Synthetic Aperture Imaging Lidar (SAIL) is an extension of conventional microwave Synthetic Aperture Radar (SAR) to much shorter wavelengths (by a factor of about 100,000) This kind of active imaging radar can offer finer resolution and better image feature which is closer to optical image In this paper, we introduce our laboratory-scale SAIL system in detail, elaborate difficulties that we have solved and will solve, and report our infrared optical synthetic aperture image of a fixed, diffusely scattering target with an aperture moving along with a sliding guide

Approach for airborne radar ISAR imaging of ship target

Abstract: Ship target ISAR imaging has significant meaning in maritime surveillance and traffic management in vast sea areas. This paper propose a novel approach for long observation time of ship target from airborne radar. First, a second-order generalised keystone formatting method is used to compensate for the range curvature induced by long integration time. Secondly, estimate the target motion parameter by virtue of time frequency techinque(WVD) and reomve the quadratic term of slow time, then use the second- order keystone formatting again to eliminate the residual range walk. So the coupling of the range and azimuth term are completely removed. At last, the clear ISAR image can be obtained. Both numerical and experimental results are provided to demonstrate the performance of the proposed method. (4 pages)

Chirp scaling algorithm for parallel bistatic SAR data processing

Abstract: This paper discusses parallel bistatic synthetic aperture radar (SAR) processing using chirp scaling algorithm. The key step is to use an analytical form of the signal spectrum derived by the geometry-based bistatic formula (GBF) method. With the above formula, a chirp scaling (CS) algorithm is proposed for azimuth-shift-invariant bistatic SAR processing. The presented algorithm can well resolve the range variation of motion through range cell(MTRC) for bistatic SAR, and requires no interpolate; it requires only FFTs and complex multiplies, these attributes lead to efficient implementations of FFT-based signal processors and high speed parallel processors; it can be used for high resolution image formation.

A novel method for ISAR imaging of ship target

Abstract: High resolution ISAR (inverse synthetic aperture radar) imaging and recognition of ship target is very important for many applications. Although the principle of ISAR imaging of ship target on the sea is the same as that of flying target in the sky, the former usually has more complex motion (fluctuation with the oceanic waves) than the latter, which makes the motion compensation very difficult. However, the change of phase chirp rate caused by the complex motion of ships will deteriorate the azimuth focusing quality. In this paper, we first model the complex motion of ship target with cubic phase terms (parameterized on chirp rate and its change rate), then a new ISAR imaging method, referred to as TC- DechirpClean, is proposed, which estimates the chirp rate and the change rate of chirp rate of all scatters in the time-chirp distribution plane. Both numerical and experimental results are provided to demonstrate the performance of the proposed method.

Range-time backprojection for 3D shape estimation of small space debris

Abstract: A coherent backprojection based approach is presented for 3D shape estimation of small debris in space. The approach utilizes the fact that space debris is in high-speed spinning motion. Making use of the modulated range envelope and Doppler spreading, a backprojection maps the data into a three-dimensional parameter domain, and the spatial coordinates of scatterers can be extracted to reconstruct 3D shape. In most of recent papers on the imaging of space debris or rotating targets, the rotation from the translational motion is assumed to be neglectable, while in our approach the backprojection is combined with a Fourier transform to deal with the rotation of translational motion and full coherent accumulation can be achieved. The approach is robust in the occurrence of serious profile overlapping and strong noise. Simulations confirm its validity and good performance.

High azimuth resolution wide swath imaging based on the intrapulse spotlight SAR

Abstract: With respect to the contradiction between high azimuth resolution and wide swath, the intrapulse spotlight synthetic aperture radar (SAR) mode is presented to achieve high azimuth resolution wide swath imaging Firstly, the model of intrapulse spotlight SAR is established, and then the characteristic of echoes in this mode is analyzed in detail A conclusion that the intrapulse scanning can make point targets in the different azimuth subswaths ambiguous is given The degrees of freedom along the pitching direction are used to remove the range ambiguities In the intrapulse spotlight SAR mode, the long synthetic aperture acquired by intrapulse scanning technique is used to realize high azimuth resolution Meanwhile a low pulse repetition frequency (PRF) is adopted to achieve wide swath Results of simulation show the effectiveness of this method

Comparison of several methods for high speed detection target with narrow bandwidth

Abstract: A new method dealing with high speed target (HST) detection in pulse-Doppler (PD) radar is proposed By utilizing Keystone Transform (KT) and linear range walk rectification, the range walk can be removed completely The method is also compared with the Hough Transform (HT) and Complex Radon Transform (CRT) The simulated data validates the method and the analysis

Experimenttation system of synthetic aperture imaging lidar

Abstract: Synthetic aperture imaging lidar is an active new imaging system, which can offer a finer azimuth resolution than the SAR system. An indoor system of synthetic aperture imaging lidar is given, which is a demonstration about synthetic aperture to image rotating objects. Firstly, the basic principle is introduced. Then, the basic method and key techniques are analyzed. After that an improved system is given with the transmitting and the receiving lens apart from each other which can eliminate the interference efficiently. Finally, the block diagram and the result of imaging system are given, which prove the validity of the system and the feasibility of the synthetic aperture techniques in optical domain.

Azimuth preprocessing for monostatic and bistatic spotlight synthetic aperture radar maging based on spectral analysis convolution

Abstract: Dechirping is a technique widely used to reduce sampling rate. It is well suited for the illumination of small scenes. In this paper, we extend this idea to mono/bistatic spotlight synthetic aperture radar (SAR) imaging. An azimuth preprocessor based on the spectral analysis (SPECAN) convolution is presented. The convolution overcomes the Doppler aliasing of echoed signals, while the wavenumber analytic formula keeps unchanged. Since the spatial characteristic of the signal is preserved, the preprocessing is well compatible with conventional focusing approaches, such as chirp scaling algorithm and frequency scaling algorithm The proposed method is validated by simulations in both monostatic and bistatic cases.