Brian D. Rigling

Polar format algorithm for bistatic SAR

Matched filtering (MF) of phase history data is a mathematically ideal but computationally expensive approach to bistatic synthetic aperture radar (SAR) image formation. Fast backprojection algorithms (BPAs) for image formation have recently been shown to give improved O(N/sup 2/ log/sub 2/N) performance. An O(N/sup 2/ log/sub 2/N) bistatic polar format algorithm (PFA) based on a bistatic far-field assumption is derived. This algorithm is a generalization of the popular PFA for monostatic SAR image formation and is highly amenable to implementation with existing monostatic image formation processors. Limits on the size of an imaged scene, analogous to those in monostatic systems, are derived for the bistatic PFA.

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.

Modulus constraints in adaptive radar waveform design

Within the taxonomy of adaptive waveform generation methodologies is the family of arbitrary waveform design algorithms, which are capable of designing both the modulus and phase of a complex-valued waveform in response to changes in the operational environment of the sensor. Algorithms of this kind have been the subject of renewed research interest as a consequence of the relatively recent advances in linear RF power amplifiers, arbitrary waveform generators, and computational capability. In this paper, we use hardware considerations to argue that constraints on the maximum waveform modulus will generally supersede the total energy constraint commonly found in the literature. In order to illustrate the deleterious effects on system performance that can arise when these modulus constraints are not accounted for, we subjected recently published waveform design algorithms to maximum modulus limitations in simulation, and we present the results here. We also propose a novel arbitrary waveform design algorithm that accounts for both maximum modulus constraints and constraints on the waveformpsilas autocorrelation function. Simulation results that demonstrate the efficacy of this algorithm are presented.

Cramér-Rao Bounds for UMTS-Based Passive Multistatic Radar

Owing to the favorable ambiguity function properties and the increased deployment, mobile communications systems are useful for passive bistatic radar applications. Further, simultaneously using multiple illuminators in a multistatic configuration will improve the radar performance, providing spatial diversity and increased resolution. We compute modified Cramér-Rao lower bounds (MCRLB) for the target parameter (delay, Doppler) estimation error using universal mobile telecommunications system (UMTS) signals as illuminators of opportunity for passive multistatic radar systems. We consider both coherent and non-coherent processing modes. These expressions for MCRLB are an important performance metric in that they enable the selection of the optimal illuminators for estimation.

Taylor expansion of the differential range for monostatic SAR

The polar format algorithm (PFA) for spotlight synthetic aperture radar (SAR) is based on a linear approximation for the differential range to a scatterer. We derive a second-order Taylor series approximation of the differential range. We provide a simple and concise derivation of both the far-field linear approximation of the differential range, which forms the basis of the PFA, and the corresponding approximation limits based on the second-order terms of the approximation.

Phase Retrieval for Radar Waveform Optimization

An important problem in radar waveform optimization is the synthesis of discrete time constant modulus signals from Fourier magnitude data. Iterative algorithms for solving this problem have been proposed in the literature, but the algorithms are only applicable in limited cases, and the convergent behavior of these algorithms has not been established. We connect waveform design to the well-studied problem of phase retrieval. This is useful for explaining the success of the proposed iterative methods. We generalize and extend the existing algorithms to handle the case in which the dimensions of the time domain waveform and the frequency domain data are unequal, and we provide a convergence analysis. We also relate the phase retrieval problem to the problem of synthesizing discrete time constant modulus signals from power spectral density (PSD) data, which is different and more appropriate for the waveform design problem. We compare the iterative methods to direct search gradient methods for both problems, and establish that the proposed algorithms can provide comparable performance with reduced computational complexity.

Motion measurement errors and autofocus in bistatic SAR

This paper discusses the effect of motion measurement errors (MMEs) on measured bistatic synthetic aperture radar (SAR) phase history data that has been motion compensated to the scene origin. We characterize the effect of low-frequency MMEs on bistatic SAR images, and, based on this characterization, we derive limits on the allowable MMEs to be used as system specifications. Finally, we demonstrate that proper orientation of a bistatic SAR image during the image formation process allows application of monostatic SAR autofocus algorithms in postprocessing to mitigate image defocus.

Effect of height to width ratio on K and CMOD solutions for a single edge cracked geometry with clamped ends

Abstract Series expressions for the stress intensity factor ( K ) and crack mouth opening displacement (CMOD) were developed for a single edge cracked geometry with clamped ends using finite element analysis. The solutions are valid for crack length to width ratio ( a / W ) in the range 0⩽ a / W ⩽0.9 and height to width ratio ( H / W ) in the range 2⩽ H / W ⩽10. Experiments conducted using MSE(T) specimens with H / W =3, 6 and 9 and compact tension specimens verified the applicability of the proposed solutions.

Micro-Range/Micro-Doppler Decomposition of Human Radar Signatures

Recently, the use of micro-Doppler radar signatures for target classification has become an area of focus, in particular for the case of dynamic targets where many components are interacting over time. To fully exploit the signature information, individual scattering centers may be automatically extracted and associated over the full target observation. The availability of ultrafine radar range resolution, or micro-range resolution, aids this process immensely. This paper proposes one such algorithm. The proposed method uses the well-known nonlinear least squares (NLS) and expectation-maximization (EM) algorithms. As shown, leveraging fine range and Doppler resolution allows human signatures to be decomposed into the responses of constituent body parts. The algorithm is experimentally validated against a number of measured human-radar data sets.

Ambiguity Function Analysis for UMTS-Based Passive Multistatic Radar

There has been a growing interest in passive radar systems in the research community over the last decade because of the several merits they offer, including ease of deployment, low cost, and non-detectability of the receivers. During the same period, the idea of distributed MIMO radar and its advantages under the coherent and non-coherent operating scenarios has been extensively studied. Keeping these benefits it mind, in this paper, we consider a UMTS-based passive multistatic radar with distributed antennas. We compute the ambiguity profiles of this radar system under both the coherent and non-coherent modes. The non-coherent processing mode improves the target detection performance by obtaining spatially diverse looks of the target. On the other hand, coherent processing enhances the resolution of target localization. We use numerical examples to demonstrate our analytical results.