Shunping Xiao

General Polarimetric Model-Based Decomposition for Coherency Matrix

Orientation angle compensation was incorporated into model-based decomposition to cure overestimation of the volume scattering contribution for interpretation of polarimetric synthetic aperture radar (PolSAR) data. The compensation is based on rotating the coherency matrix to minimize the cross-polarization term. However, this processing cannot always guarantee that the double- and odd-bounce scattering components will be rotated back to zero orientation angle and left with zero cross-polarization power. As a result, built-up patches with large orientation angles may still suffer from the scattering mechanism ambiguity. In this paper, double- and odd-bounce scattering models were generalized to fit the cross-polarization and off-diagonal terms, by separating their independent orientation angles. A general decomposition framework is proposed that utilizes all elements of a coherency matrix. The residual minimization criterion is used for model inversion. All the model parameters are simultaneously obtained using a nonlinear least squares optimization technique. The manual intervention, branch conditions, and negative power issues are avoided. The performance and advantages of this approach are demonstrated and evaluated with spaceborne L-band ALOS/PALSAR and airborne X-band Pi-SAR PolSAR data sets. Comparison studies are also carried out and demonstrate that further improved decomposition performance is achieved by the proposed method, especially in oriented built-up areas.

Modeling and Interpretation of Scattering Mechanisms in Polarimetric Synthetic Aperture Radar: Advances and perspectives

Recent advances in scattering modeling and model-based decomposition theorem were reviewed. The notable achievements include orientation compensation processing, nonnegative eigenvalue constraint, generalized scattering models, complete information utilization, full-parameter inversion strategy, and the polarimetric-interferometric decomposition scheme. These advances contribute to make scattering models more adaptive, better fit observations and guarantee physically meaningful decomposition solutions. The key features of these advances have been summarized. Performance evaluation and further development perspectives were also discussed. One promising way is to fuse multiple data to better model scattering mechanisms, such as the polarimetric-interferometric modeling attempts. Besides, with the progress in PolSAR sensors, imaging modes (e.g., bistatic, hybrid-polarization and multi-incident-angle modes) and application requirements, the development of specific scattering mechanism interpretation techniques, multiangular decomposition, and compact/hybrid decomposition techniques are also highly preferred.

Estimation of Precession Parameters and Generation of ISAR Images of Ballistic Missile Targets

The micro-motion properties of the rotational symmetry ballistic targets (BTs) are analyzed in the work presented here. A method for the estimation of precession frequency and the precession angle is proposed based on the polarization properties of the rotational symmetry ballistic targets (BTs). Compared with the traditional precession frequency estimation method, the estimated spectra of the harmonic frequencies are considerably smaller. In addition, an inverse synthetic aperture radar (ISAR) imaging technique based upon the micro-motion of BTs is proposed. The theoretical conclusions are confirmed by the application of the experimental data.

Main-Lobe Jamming Suppression Method of using Spatial Polarization Characteristics of Antennas

As interferences are introduced from a main-lobe direction, which results in target signals being masked by interference, traditional adaptive beamforming and eigen-subspace projection methods cannot suppress main-lobe interferences effectively. A novel interference suppression method is proposed that processes the sample data by using the scanning property of a single polarized antenna. The orthogonal polarization decomposition and polarization estimation of the receiving signal based on the spatial polarization characteristics of the antenna are realized so that the interference is diminished. The effect of an elevation measurement error on interference suppression performance is eliminated by design spatial multinotch virtual polarization filtering. Theoretical and simulation results show that it made single polarized radar own a polarization information processing ability that improved radar working performance.

Maximum Likelihood Approach to the Estimation and Discrimination of Exoatmospheric Active Phantom Tracks using Motion Features

An optimal kinematics-based discrimination algorithm is presented for the nearly real-time discrimination of exoatmospheric active phantom (deception) tracks against other physical targets (PTs). The new approach uses a batch-processing maximum likelihood estimator (MLE) to precisely estimate the deception range of decoys from raw radar tracking measurements by using motion features. Hence once these parameters are estimated, they can serve as direct statistics to initiate a discrimination. By augmenting the state vector with deception parameters, explicit expressions of motion models of decoys in the radar centered East-North-Up (ENU) coordinate system (CS) and spherical-CS are derived. Based on these models, the theoretical Cramer-Rao lower bound (CRLB) and the observability of the deception parameters are also analyzed. A Levenberg-Marquardt method is employed to obtain more robust estimate of these parameters, and the estimated parameters combined with the CRLB are used for designing discrimination algorithm. The simulations verify the feasibility of the algorithm. Furthermore, the discrimination performance due to the influence of radar position, data rate, and radar measurement error are also covered. The advantage of the algorithm lies in that it can position the warhead precisely as well as discriminating active decoys simultaneously when compared with the traditional 6-dimensional orbit determination methods.

Bistatic scattering centres of cone-shaped targets and target length estimation

The bistatic scattering centres are commonly modeled as the fixed scattering centres for imaging; however, the location of the bistatic scattering centre changes with the bistatic geometry in some real scenes. This paper focuses on the bistatic scattering centres of cone-shaped targets and considers how to utilize the length of the bistatic high-resolution range profile (HRRP) for target identification. Firstly, the locations of the bistatic scattering centres on the edge of a cone-shaped target are deduced with the method of equivalent currents, which are the intersection points of the edge and the plane constructed by the symmetry axis and the bisector of the bistatic angle. Then, based on the above conclusion, the wideband echo model and bistatic HRRP of a cone-shaped target is deduced. Then, the relation between the length of the bistatic HRRP and target length is deduced, which is useful for target identification. Finally, the bistatic HRRPs of cone-shaped targets are calculated via the Feko software and the calculated results validate the theoretical analysis. This research provides an exact mathematics model for the echo simulation, imaging, feature extraction and identification of cone-shaped targets in the bistatic radar.

Spatial polarization characteristics and scattering matrix measurement of orthogonal polarization binary array radar

Polarimetry is an important trend in the development of modern radar. The technique for measuring polarization scattering property of the target is the key for polarization radar realization, but it faces challenges in engineering. Here, a new theoretical model for target scattering characteristic measurement radar, named orthogonal polarization binary array radar (OPBAR), is proposed. The spatial polarization characteristics of the radar antennas are addressed. A new polarimetric algorithm that needs only one channel is designed. The polarization scattering matrix measurement can be implemented by processing received signal in a short time interval while antenna’s beam mechanically scans the target. Through compactness field microwave dark room experiment, measurments of dynamic broadband polarimetry on OPBAR have been conducted and the validity of research work has been demonstrated. The result is helpful to exploiting the capability of current radar systems and enhancing their information acquiring and processing capacity.

Imaging of Spinning Targets via Narrow-Band T/R-R Bistatic Radars

The 2-D image of a spinning target obtained by monostatic radar is modified by the angle between the spinning axis and the radar line of sight, so it usually cannot describe the real size of the target. The T/R-R bistatic radar is proposed to solve this problem. First, the bistatic geometry and bistatic echo signals of a spinning target are modeled. Then, a novel 2-D imaging algorithm is presented based on the connections between the mono- and bistatic echoes of the same scatterer and the classical Hough transform, allowing both the mono- and bistatic 2-D images of the spinning target to be obtained simultaneously. The theoretical analysis is carried out by the electromagnetic calculation and numerical simulations.

Novel research on main-lobe jamming polarization suppression technology

A novel main-lobe blanketing interference suppression method which named as spatial virtual multiple channel concurrent polarization filter technology is proposed. It processes sample data using the slow varied polarization property of a scanning antenna. The orthogonal polarized signal and polarization states of the receiving signal can be obtained. The optimal polarization is then calculated for use in polarization filtering to achieve the objective of suppressing noise jamming. The effect of elevation measurement error on interference suppression performance is eliminated by concurrent processing. Theoretical and simulation results show that, this technology enabled self-polarization information processing for single polarized radar which improved its working performance.

A rapid solution of a kind of 1D Fredholm oscillatory integral equation

How to solve oscillatory integral equations rapidly and accurately is an issue that attracts special attention in many engineering fields and theoretical studies. In this paper, a rapid solution method is put forward to solve a kind of special oscillatory integral equation whose unknown function is much less oscillatory than the kernel function. In the method, an improved-Levin quadrature method is adopted to solve the oscillatory integrals. On the one hand, the employment of this quadrature method makes the proposed method very accurate; on the other hand, only a small number of small-scaled systems of linear equations are required to be solved, so the computational complexity is also very small. Numerical examples confirm the advantages of the method.