Scattering Center Model Research Articles

A novel scheme for global scattering center modeling of radar targets

A novel scheme for extracting the global scattering center model of radar targets is proposed in this paper. The 2D/3D scattering center models can be reconstructed based on the wideband measurements at different viewing angles. The sphere spreading of the 1D scattering center projections is exploited. The 1D-2D/3D scatterer map (OTSM) is designed to manifest the high dimensional scattering characteristic of radar targets. The Hough transform and the least squares method are used to extract the stable scattering centers and their scattering coefficients. This modeling method does not need a high density of the spatial grid, which greatly cuts down the necessary original data. The model built in this way describes the stable point scattering mechanisms in a large spatial extent and can be extrapolated to other frequencies in the optical region. Examples verify the validity of both the model and the method.

Improvement of the scattering center extraction by using the modified approximate prolate series interpolants

AbstractThe three‐dimensional (3D) scattering center model of a complex target can be obtained from the 3D inverse synthetic aperture (ISAR) image by using the CLEAN algorithm. To form the ISAR image from the results of a shooting‐and‐bouncing‐ray (SBR) analysis, the image is updated on a ray‐by‐ray basis using a ray‐spread function, which turns out to be a “sinc” function. The “sinc” function does not decay rapidly, yielding a harsh trade‐off: in case the full “sinc” function is used, the algorithm becomes computationally intense. On the other hand, if it is truncated, convergence problems arise. To solve this trade‐off problem, the use of a band‐limited interpolant function, namely, modified approximate prolate series (MAPS) is proposed instead of the “sinc” function. The suggested MAPS can be shown to have better truncation error bounds than other ray spread functions. By using the suggested MAPS functions, the sidelobe artifacts are minimized and the computational complexity is decreased while extracting the scattering centers with correct positions, amplitudes, and better resolution. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1623–1628, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22509

Analytic performance bounds on estimates of scattering center parameters

Cramer-Rao bounds (CRBs) on the estimates of the main scattering center parameters, i.e., the position, intensity and geometry type, are presented in analytic forms. The resolution limit for wideband radar and the SNR threshold for the correct identification of the geometry type parameter of scattering centers are further deduced. Though the results are obtained from the CRB matrix for damped exponentials (DE) after many approximations and simplifications, their validity and adaptability for geometric theory of diffraction (GTD) based scattering center model have been verified both numerically and experimentally.

A two-distribution compounded statistical model for Radar HRRP target recognition

In the statistical target recognition based on radar high-resolution range profile (HRRP), two challenging tasks are how to deal with the target-aspect, time-shift, and amplitude-scale sensitivity of HRRP and how to accurately describe HRRPs statistical characteristics. In this paper, based on the scattering center model, range cells are classified, in accordance with the number of predominant scatterers in each cell, into three statistical types. After resolving the three sensitivity problems, this paper develops a statistical model comprising two distribution forms, i.e., Gamma distribution and Gaussian mixture distribution, to model echoes of different types of range cells as the corresponding distribution forms. Determination of the type of a range cell is achieved by using the rival penalized competitive learning (RPCL) algorithm, while estimation for the parameters of Gamma distribution and Gaussian mixture distribution by the maximum likelihood (ML) method and the expectation-maximization (EM) algorithm, respectively. Experimental results for measured data show that the proposed statistical model not only has better recognition performance but also is more robust to noises than the two existing statistical models, i.e., Gaussian model and Gamma model.

A new feature extraction method using the amplitude fluctuation property of target HRRP for radar automatic target recognition

Due to the aspect sensitivity of high-resolution range profile (HRRP), traditional radar HRRP target recognition methods usually use average profile within some target-aspect region as the target-aspect template. Actually, the amplitude fluctuation property of target HRRP also represents some feature information of the target. Based on the scattering center model, a new feature extraction method using the amplitude fluctuation property of target HRRP is proposed in this paper. The weighted HRRP feature extracted by the new method can represent the scatterer distribution in every range cell, thereby it can describe the scattering property of the target better. The experimental results based on measured data show that the new feature extraction method can greatly improve recognition performances.

BROADBAND SCATTERING DATA INTERPOLATION BASED ON A RELAXED ADAPTIVE FEATURE EXTRACTION ALGORIGHM

A method using a relaxed adaptive feature extraction algorithm is investigated to interpolate broadband, high-frequency scattering from sparse, undersampled data. First, the adaptive feature extraction is extended to include a frequency-dependent scattering center model in order to better-describe broadband scattering physics from a complex target per the geometrical theory of diffraction. Second, the parameterization of the model is relaxed for more accurate extractions and a sparser model representation using fewer samples. Comparative results are presented for the relaxed versus the non-relaxed adaptive feature extraction algorithm for hypothetical examples and a numerically-solved ogive body of revolution. The relaxed algorithm is more computationally expensive, but results in significantly improved performance. The technique enhances adaptive feature extraction performance for broadband interpolation. 100 Raynal, Moore, and Ling

Radar HRRP target recognition based on higher order spectra

Radar high-resolution range profile (HRRP) is very sensitive to time-shift and target-aspect variation; therefore, HRRP-based radar automatic target recognition (RATR) requires efficient time-shift invariant features and robust feature templates. Although higher order spectra are a set of well-known time-shift invariant features, direct use of them (except for power spectrum) is impractical due to their complexity. A method for calculating the Euclidean distance in higher order spectra feature space is proposed in this paper, which avoids calculating the higher order spectra, effectively reducing the computation complexity and storage requirement. Moreover, according to the widely used scattering center model, theoretical analysis and experimental results in this paper show that the feature vector extracted from the average profile in a small target-aspect sector has better generalization performance than the average feature vector in the same sector when both of them are used as feature templates in HRRP-based RATR. The proposed Euclidean distance calculation method and average profile-based template database are applied to two classification algorithms [the template matching method (TMM) and the radial basis function network (RBFN)] to evaluate the recognition performances of higher order spectra features. Experimental results for measured data show that the power spectrum has the best recognition performance among higher order spectra.

Recognising aircraft without radar databases

To identify enemy aircraft effectively, radar systems depend on a database of known targets. This article outlines a system which can be used if radar signatures are not available. It considers classification of aircraft using data derived from non-radar sources. The key approach adopted here is the use of a scattering-centre model from which prominent scattering features on each candidate aircraft are derived. These features are then compared with features derived from measured profiles in order to classify the radar target. The results given here support the notion of a model consisting of a small number of scattering centres, but indicate that the variation of backscatter with aspect angle from these scattering centres may be quite complicated.

Scattering of sonic booms by anisotropic turbulence in the atmosphere

An earlier paper [J. Acoust. Soc. Am. 98, 3412-3417 (1995)] reported on the comparison of rise times and overpressures of sonic booms calculated with a scattering center model of turbulence to measurements of sonic boom propagation through a well-characterized turbulent layer under moderately turbulent conditions. This detailed simulation used spherically symmetric scatterers to calculate the percentage of occurrence histograms of received overpressures and rise times. In this paper the calculation is extended to include distorted ellipsoidal turbules as scatterers and more accurately incorporates the meteorological data into a determination of the number of scatterers per unit volume. The scattering center calculation overpredicts the shifts in rise times for weak turbulence, and still underpredicts the shift under more turbulent conditions. This indicates that a single-scatter center-based model cannot completely describe sonic boom propagation through atmospheric turbulence.

3D scattering center representation of complex targets using the shooting and bouncing ray technique: a review

We present an automated technique to extract the three-dimensional scattering-center model of a target from its geometrical CAD model. The technique is based on the shooting and bouncing ray (SBR) method. In this article, we first review the basic concepts behind the three-dimensional scattering-center-extraction algorithm. Next, we present application examples of signature-data compression and radar-feature extraction, based on the scattering centers extracted from complex targets using such a methodology. We conclude by identifying some future areas of research.

A deterministic method for generating a scattering-center model to reconstruct the RCS pattern of complex radar targets

This paper presents a deterministic method to establish the scattering-center model for complex radar targets. By this method, high frequency techniques including physical optics, physical theory and diffraction and shooting and bouncing rays are used to establish scattering centers. Numerical results show that, by using this method with only single-frequency scattering centers at large aspect increments, the RCS pattern at finer aspect increments is well reconstructed; besides, it can be extended to predict the RCS pattern at any frequency of interest in a required narrow bandwidth. Good agreement between direct RCS calculation, scattering-center model and measured results is obtained.

A global scattering center representation of complex targets using the shooting and bouncing ray technique

We present a methodology to extract a global scattering center model a complex target. Using the shooting and bouncing ray technique, we first extract the three-dimensional (3-D) scattering center representations of the target at various aspect angles. Next the correspondence between scattering centers across angles are established by utilizing 3-D location information. The data are grouped based on 3-D scattering center locations and are organized in the form of angular visibility maps. Such data organization gives good insights into target physics and feature stability. Furthermore, we define a stability measure to quantitatively rank order the scattering centers based on their angular stability. Finally, we demonstrate the usefulness of such stable features by carrying out a five-target template-based matching experiment to estimate the angular pose of an unknown target.

Scattering center parameterization of wide-angle backscattered data using adaptive Gaussian representation

We present a scattering center extraction algorithm to parameterize the backscattered data from complex targets collected over large angular apertures. This parameterization is based on a scattering center model of the target, but includes an aspect-dependent amplitude function for each scattering center. A two-dimensional (2-D) adaptive Gaussian representation (AGR) algorithm is used to extract the position and the amplitude function associated with each scattering center. The algorithm is tested with data generated by the Xpatch radar simulation code as well as chamber measurement data. The results show that a very good compression ratio can be achieved, resulting in a compact scattering center model of the target. Once such model is available, we can easily reconstruct range profiles and ISAR images at any aspect on the same plane with good accuracy.

Three-dimensional scattering center extraction using the shooting and bouncing ray technique

We present a technique to extract the three-dimensional (3-D) scattering center model of a complex target. Using the shooting and bouncing ray technique, we first generate the 3-D inverse synthetic aperture radar (ISAR) image of the target based on a one-look ISAR algorithm. In step two, we use the image processing algorithm CLEAN to extract the 3-D position and strength of the scattering centers from the 3-D ISAR image. Various implementation issues related to computation time and memory are addressed and an efficient scheme is presented to accomplish the 3-D scattering center extraction. Several examples ranging from simple canonical structures to complex targets are presented to demonstrate the validity of the extraction scheme and the usefulness of the resulting 3-D scattering center model.

Radar target identification

The authors discuss the aspects of the radar target/identification problem which have made progress slow and difficult. They summarize their research program and discuss the mathematical foundations for solving the problem. To simplify the discussion, only aircraft-type targets are considered, and clutter is ignored. Target-library problems, are examined in some detail, including the proposed use of scattering-center models to mitigate problems and related electromagnetic-modeling considerations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A polarimetric model for the recovery of the high-frequency scattering centers from bistatic-monostatic scattering matrix data

The objective of this investigation is to develop multistatic electromagnetic identification/discrimination algorithms using the complete polarimetric scattering data. At high frequencies the electromagnetic scattering from a complex object is modeled by certain scattering centers. The high-frequency (physical optics) bistatic and monostatic scattering matrix properties of a flat plate model of such a scattering center are developed in detail. For the complex target representations, the single scattering center results can be extended to two and three scattering center models. It is suggested that the knowledge of the locations and the local geometries of these scattering centers can be useful in developing identification and pattern recognition algorithms.

Low-energy solar protons and alphas as probes of the interplanetary medium: The May 28, 1967, solar event

The low-energy solar protons and alpha particles detected during the May 28 (day 148), 1967, solar flare are used as ‘probes’ to investigate the properties of the interplanetary medium during the course of the event. The lower energy fluxes exhibit characteristics of particle storage either at the sun or in interplanetary space. The higher energy particle fluxes exhibit ‘classical’ west limb flare profiles and are fit both to a simple isotropic diffusion-with-boundary model and to a radial dependent scattering center model. The diffusion coefficient model of Jokipii is used with the results of a fit to the exponential decay of the event to predict an ƒ−3 dependence of the power spectral density of the interplanetary magnetic field fluctuations (assuming a boundary location independent of rigidity). The ratio of particle fluxes before and after a sudden, discontinuous flux decrease (attributed to a sector boundary) is found to be ∼R³ for protons and ∼R6 for alphas for particles with rigidities ≲ 200 Mv. Significant velocity dispersions are discovered in three of the flux modulations during the onset stage of the event. The velocity dispersions in one of these modulations could be interpreted as due to a modulating region located ∼0.03 AU from the earth. It is speculated that this region was responsible for an sc at the earth some two hours later.