Rajan Bhalla

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.

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.

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.

Image domain ray tube integration formula for the shooting and bouncing ray technique

A simple image domain ray tube integration formula is presented to efficiently compute the inverse synthetic aperture radar (ISAR) image of a complex target by the shooting and bouncing ray (SBR) technique. Contrary to the conventional approach where the ISAR image is obtained by inverse Fourier transforming the computed scattered field data over frequency and aspect, this image domain formula gives the contribution of each ray to the overall ISAR image directly. Under the small angle approximation and utilizing the bistatic-monostatic equivalence, the image domain ray tube integration formula is determined in closed form. Simulation results using the SBR-based code “Xpatch” show that the direct image domain method results in good image quality and superior time performance when compared to the conventional frequency aspect approach.

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.

ASAR-antenna synthetic aperture radar imaging

The antenna synthetic aperture radar (ASAR) imaging concept is introduced. We present the ASAR imaging algorithm to pinpoint the locations of secondary scattering off a platform from antenna radiation data. It is shown that a three-dimensional (3-D) ASAR image of the platform can be formed by inverse Fourier transforming the multifrequency, multiaspect far-field radiation data from an antenna mounted on the platform. This concept is demonstrated using the computed radiation data from the code Apatch, which employs the shooting and bouncing ray (SBR) technique. Furthermore, we develop a fast ASAR algorithm specially tailored for the SBR approach. By taking advantage of the ray tracing information within the SBR engine, we demonstrate that the fast approach can result in the same quality of image as the frequency-aspect algorithm at only a fraction of the computation time.

ISAR Image Formation Using Bistatic Data Computed from the Shooting and Bouncing Ray Technique

The feasibility of utilizing bistatic scattered field data to obtain the microwave ISAR image of a target is investigated. The principle and results of the bistatic imaging algorithm are presented. It is shown that the ISAR image can be reconstructed by Fourier inversion of the bistatic scattered field data under the physical optics approximation. Bistatic scattered field data is faster to simulate using the shooting and bouncing ray technique than monostatic scattered field data hence the bistatic scheme results in time savings. Monostatic and bistatic ISAR images are presented for different targets. The tradeoff between time savings and image fidelity for the two schemes is discussed.

A radiation center representation of antenna radiation patterns on a complex platform

A sparse model of the antenna radiation pattern on a complex platform is presented. This representation is based on a point radiator model that describes the radiation pattern by a collection of radiation centers on the platform. The methodology for obtaining the radiation center model is presented. It entails first generating the three-dimensional (3-D) antenna synthetic aperture radar (ASAR) imagery of the platform and then parameterizing the resulting image by a collection of point radiators via the CLEAN algorithm. It is shown that once such a representation is obtained, we can reconstruct and extrapolate antenna radiation patterns over frequencies and aspects with good fidelity, thus achieving high data compression ratio. Furthermore, it is shown that the resulting radiation center information can be used to pinpoint cause-and-effect in platform scattering and provide important guidelines for reducing platform effects.

Fast ASAR image formation using the shooting and bouncing ray technique

We have recently devised a diagnostic algorithm for imaging antenna-platform interactions from antenna radiation data. The algorithm, termed ASAR (antenna synthetic aperture radar) imaging, utilizes multi-frequency, multi-aspect radiation data and Fourier processing to create a 3D map of the platform showing the locations of dominant secondary radiation on the platform. Such an algorithm can be used to process either measurement data or computed data from electromagnetic solvers. In this paper, we consider the case when the SBR (shooting and bouncing ray) approach is used to simulate the antenna radiation data. It is shown that a fast ASAR imaging algorithm especially tailored for the SBR approach can be derived. By taking advantage of the ray tracing information within the SBR engine, we will show that the ASAR image can be generated directly in the image domain without resorting to any multiple frequency-aspect calculations. Such an idea is similar to the image-domain ISAR formation process we have reported previously (1995). Furthermore, we can apply an FFT-based algorithm to speed up the ASAR image formation time. Using such a fast approach, it is possible to obtain the same quality of ASAR image as frequency-aspect approach at only a fraction of the computation time (minutes versus hours).

Near-field signature prediction using far-field scattering centers extracted from the shooting and bouncing ray technique

We present a technique to predict the near-field radar cross section (RCS) of a target using the far-field scattering centers extracted from the shooting and bouncing ray (SBR) technique. The results generated using this methodology are verified against the brute-force SBR calculations for near-field scenarios. It is demonstrated that this technique is a fairly accurate and very efficient way to generate near-field RCS data provided that the transceiver is not very close to the target.