Julie Ann Jackson

Canonical Scattering Feature Models for 3D and Bistatic SAR

This paper develops three-dimensional (3D), bistatic parametric models that describe canonical radar scattering responses of several geometric objects. These models find use in inverse scattering-based processing of high-frequency radar returns. Canonical feature models are useful for extracting geometry from synthetic-aperture radar (SAR) scattering measurements and as feature primitives for automatic target recognition (ATR) and scene visualization. Previous work has considered monostatic feature models for two-dimensional (2D) radar processing; we extend this work to consider bistatic and 3D radar apertures. In the work presented here, we generalize geometric theory of diffraction (GTD) solutions for several scattering mechanisms in a plane. Products of these planar mechanisms in azimuth and elevation are used to produce 3D bistatic scattering models for six canonical shapes: a rectangular plate, dihedral, trihedral, cylinder, top-hat, and sphere. The derived models are characterized by a small number of parameters, and are shown to agree with results obtained from high-frequency, asymptotic scattering simulations.

Synthetic Aperture Radar 3D Feature Extraction for Arbitrary Flight Paths

We propose an algorithm for extracting multiple geometric scattering features from synthetic aperture radar (SAR) phase history collected over arbitrary, 3D monostatic or bistatic apertures. The algorithm input is complex-valued phase history; the output is a list of features and corresponding parameter estimates. We fit to the data parametric models for six canonical features. The feature extraction problem includes model order selection, shape classification, and parameter estimation. Examples include densely-sampled and sparse apertures for monostatic and bistatic scenarios.

Rethinking vehicle classification with wide-angle polarimetric SAR

Wide-angle SAR presents an opportunity to explore new methods for CV classification. Polarization features are of particular interest and various examples of wide-aperture images using flight-collected and simulated data are shown to emphasize how odd and even reflectors are revealed in the imagery. Using the well-known frequency parameter from high-frequency scattering models and the Krogager polarization decomposition, wide-angle polarimetric SAR imagery is attributed with a basis of ASC primitive targets. We observe trends when extracting ASCs from 2D images and study the behavior for 10 civilian vehicles using the AFRL Civilian Vehicle Data Dome. Passenger cars categorized as the sedan class tended to exhibit scattering by cylinders, horizontal edges, and horizontal dihedrals at low elevation angle (30°) but primarily showed horizontal cylinders and horizontal dihedrals for the case of high elevation angle (60°). Likewise, the dominant scatterers for the SUV class were horizontal cylinders and horizontal edges for 30° elevation and primarily horizontal cylinders and dihedrals for 60° elevation. These results suggest that there are noticeable differences between the classes when viewed as primitives in the joint frequency/polarization/wide-angle SAR feature space. Thus, rethinking vehicle classification to include efficient primitive type extraction during image formation may lead to new, near real-time vehicle classification algorithms.

WiMAX OFDM for Passive SAR Ground Imaging

Modern communication systems provide myriad opportunities for passive radar applications. Research is introduced here on the passive use of worldwide inoperability for microwave access (WiMAX) orthogonal frequency division multiplexing (OFDM) waveforms for synthetic aperture radar (SAR) ground imaging. The anatomy of the waveform is presented followed by a brief bistatic ambiguity function analysis. The monostatic and bistatic models for OFDM range compression are derived and validated with experimental data. We conclude with SAR imaging results and a discussion on future research.

Enhancement of multi-pass 3D circular SAR images using sparse reconstruction techniques

This paper demonstrates image enhancement for wide-angle, multi-pass three-dimensional SAR applications. Without sufficient regularization, three-dimensional sparse-aperture imaging from realistic data-collection scenarios results in poor quality, low-resolution images. Sparsity-based image enhancement techniques may be used to resolve high-amplitude features in limited aspects of multi-pass imagery. Fusion of the enhanced images across multiple aspects in an approximate GLRT scheme results in a more informative view of the target. In this paper, we apply two sparse reconstruction techniques to measured data of a calibration top-hat and of a civilian vehicle observed in the AFRL publicly-released 2006 Circular SAR data set. First, we employ prominent-point autofocus in order to compensate for unknown platform motion and phase errors across multiple radar passes. Each sub-aperture of the autofocused phase history is digitally-spotlighted (spatially low-pass filtered) to eliminate contributions to the data due to features outside the region of interest, and then imaged with l1-regularized least squares and CoSaMP. The resulting sparse sub-aperture images are non-coherently combined to obtain a wide-angle, enhanced view of the target.

Authorized and Rogue Device Discrimination Using Dimensionally Reduced RF-DNA Fingerprints

Unauthorized network access and spoofing attacks at wireless access points (WAPs) have been traditionally addressed using bit-centric security measures and remain a major information technology security concern. This has been recently addressed using RF fingerprinting methods within the physical layer to augment WAP security. This paper extends the RF fingerprinting knowledge base by: 1) identifying and removing less-relevant features through dimensional reduction analysis (DRA) and 2) providing a first look assessment of device identification (ID) verification that enables the detection of rogue devices attempting to gain network access by presenting false bit-level credentials of authorized devices. DRA benefits and rogue device rejection performance are demonstrated using discrete Gabor transform features extracted from experimentally collected orthogonal frequency division multiplexing-based wireless fidelity (WiFi) and worldwide interoperability for microwave access (WiMAX) signals. Relative to empirically selected full-dimensional feature sets, performance using DRA-reduced feature sets containing only 10% of the highest ranked features (90% reduction), includes: 1) maintaining desired device classification accuracy and 2) improving authorized device ID verification for both WiFi and WiMAX signals. Reliable burst-by-burst rogue device rejection of better than 93% is achieved for 72 unique spoofing attacks and improvement to 100% is demonstrated when an accurate sample of the overall device population is employed. DRA-reduced feature set efficiency is reflected in DRA models requiring only one-tenth the number of features and processing time.

Feature extraction algorithm for 3D scene modeling and visualization using monostatic SAR

We present a feature extraction algorithm to detect scattering centers in three dimensions using monostatic synthetic aperture radar imagery. We develop attributed scattering center models that describe the radar response of canonical shapes. We employ these models to characterize a complex target geometry as a superposition of simpler, low-dimensional structures. Such a characterization provides a means for target visualization. Fitting an attributed scattering model to sensed radar data is comprised of two problems: detection and estimation. The detection problem is to find canonical targets in clutter. The estimation problem then fits the detected canonical shape model with parameters, such as size and orientation, that correspond to the measured target response. We present an algorithm to detect canonical scattering structures amidst clutter and to estimate the corresponding model parameters. We employ full-polarimetric imagery to accurately classify canonical shapes. Interformetric processing allows us to estimate scattering center locations in three-dimensions. We apply the algorithm to scattering prediction data of a simple scene comprised of canonical scatterers and to scattering predictions of a backhoe.

Parametric scattering models for bistatic synthetic aperture radar

Parametric scattering center models match to radar scene attributes, aiding in automatic target recognition (ATR) and scene visualization. In this paper, we develop parametric models of canonical shapes for bistatic synthetic aperture radar (SAR).We generalize geometric theory of diffraction solutions for scattering mechanisms in a plane to develop three-dimensional models for six canonical shapes: a rectangular plate, dihedral, trihedral, cylinder, top-hat, and sphere. The proposed models provide physically relevant yet compact scattering solutions that are easily implemented for radar signal processing and ATR applications. The derived models are shown to agree with results obtained from high-frequency, asymptotic scattering simulations.

Analysis of an LTE waveform for radar applications

Previous research has shown communication waveforms have potential for passive and active radar applications. The potential of a signal is typically characterized using the ambiguity function. This paper seeks to summarize the frequency division duplex (FDD) long term evolution (LTE) downlink (DL) signal structure and illustrate its effect on the signals self and cross ambiguity functions. In addition, performance limitations resulting from the FDD LTE DL signal structure are predicted. The variability of system performance limitations is considered for variable FDD LTE DL signal parameters. Lastly, simulated range profiles are produced using a simulated FDD LTE DL signal illustrating the derived results.

Analytic Physical Optics Solution for Bistatic, 3D Scattering From a Dihedral Corner Reflector

We derive an analytic scattering model for 3D bistatic scattering from a dihedral using geometrical optics (GO) and physical optics (PO). We use GO to trace ray reflections, and we evaluate the PO integral(s) for the field scattered by each plate of the dihedral. Multiple cases of reflection geometry are considered to account for effects of the dihedral plate size and antenna aspect angles. The complex-valued (amplitude and phase) scattering response is derived. The resulting parametric scattering model is presented in terms of the vertical and horizontal co-polarization and cross-polarization responses that correspond to the outputs of industry-standard numerical prediction codes. Comparing the derived model to available codes for method of moments (MoM), shooting and bouncing rays (SBR), and parametric models (PM), we demonstrate that the derived solution achieves the same accuracy as SBR, approximates MoM, is more accurate than PM, and does so in fast computation time comparable to a PM.