Michael A. Saville

Exploiting frequency diverse array processing to improve SAR image resolution

Cross-range resolution in spotlight synthetic aperture radar (SAR) is primarily a function of the angular extent (Deltathetas) over which data is collected. In [1], the authors proposed a method for improving cross-range resolution for a given Deltathetas by use of frequency diverse array (FDA) techniques. The goal was to exploit an apparent increase in Deltathetas to improve cross-range resolution while retaining benefits of shorter synthetic apertures and integration times using a linear FDA. This paper extends those efforts and introduces the application of FDA techniques to improve range resolution.

Direct Cartesian detection, localization, and de-ghosting for passive multistatic radar

Conventional passive multistatic radar systems, which are comprised of multiple transmitters and receivers, detect and localize targets in a two-stage process. First, detections are performed independently for each bistatic transmit-receive pair. A multilateration process then uses the resulting bistatic range estimates to localize the targets in Cartesian space. Multilateration results in additional false “ghost” targets, which must be removed by a subsequent process. This paper presents a single-stage approach that performs detection, localization, and deghosting directly in Cartesian space. This approach is the generalized likelihood ratio test (GLRT) for scintillating targets, which provides improved probability of detection compared to the conventional approach by making use of available diversity gain. Furthermore, as target localization and deghosting are performed implicitly, separate localization and deghosting processes are not required. Detection performance equations are provided, as are numerical examples illustrating the inherent localization and deghosting nature of the proposed architecture.

Analysis of SAR Moving Grid Processing for Focusing and Detection of Ground Moving Targets

This paper investigates the performance of single-channel SAR-GMTI systems in the focusing and detection of translating ground targets moving in the presence of a clutter background. Specifically, focusing and detection performance is investigated by applying the Moving Grid Processing (MGP) focusing technique to a scene containing an accelerating target moving in the presence of both uniform and correlated K-distributed clutter backgrounds. The increase in detection sensitivity resulting from the focusing operation is found to result from two separable effects, target focusing and clutter defocusing. While the detection sensitivity gain due to target focusing is common for both clutter types, the gain due to clutter defocusing is found to be significantly greater for textured clutter than for uniform clutter, by approximately 5 to 6 dB in the simulated scenario under consideration. This paper concludes with a discussion of the phenomenological causes for this difference and implications of this finding for single channel SAR-GMTI systems operating in heterogeneous clutter environments.

Investigation on Genetic Algorithm for Countermeasure Technique Generator

Development of successful electronic countermeasure (ECM) techniques against target track radars is a time-consuming and expensive process. Recently, Nunez et al. reported a genetic algorithm (GA) optimization method for ECM techniques generation; this paper outlines the current effort to implement the approach with an operational radar system and to establish a methodology for arbitrary ECM signal generation in a closed-loop system. While this effort employs GA, the method applies equally to other optimization techniques. After defining the GA fitness function for a generic range gate pull off (RGPO) technique, the ECM signal is implemented with a very fast digital arbitrary waveform generator. The RGPO signal is injected into the radar environment, and the tracking radar response is measured and scored for optimization. The method is suitable for more sophisticated ECM signals and will be studied in future work.

Characterizing geolocation ambiguity responses in synthetic aperture radar: ground moving target indication

Single-channel synthetic aperture radar (SAR) can provide high quality, focused images of moving targets by utilizing advanced SAR-GMTI techniques that focus all constant velocity targets into a three-dimensional space indexed by range, cross-range and cross-range velocity. However, an inherent geolocation ambiguity exists in that multiple, distinct moving targets may posses identical range versus time responses relative to a constant velocity collection platform. Although these targets are uniquely located within a four-dimensional space (x-position, y-position, x-velocity, and y-velocity), their responses are focused and mapped to the same three-dimensional position in the SAR-GMTI image cube. Previous research has shown that circular SAR (CSAR) collection geometry is one way to break this ambiguity and creates a four-dimensional detection space. This research determines the target resolution available in the detection space as a function of different collection parameters. A metric is introduced to relate the resolvability of multiple target responses for various parametric combinations, i.e., changes in key collection parameters such as integration time, slant range, look angle, and carrier frequency.

Simulator for Velocity Gate Pull-Off electronic countermeasure techniques

This paper explores the use of implementing deception waveforms in the space-time adaptive processing (STAP) model for efficient waveform optimization in hardware-in-the-loop simulation. By understanding range gate pull-off (RGPO) techniques developed in a generic form, velocity gate pull-off (VGPO) technique models can be explored in a similar manner. The VGPO mathematical models are developed using a STAP framework to simplify the optimization cost function. The STAP model, implemented in MATLAB, is solely used to represent a series of electronic countermeasure signals. Using the proposed implementation, the ECM waveform can be injected in the HILS architecture via simulation or hardware. Initial results reveal that the pulse-indexed STAP representation is M times better than a time-indexed signal representation while naturally including coordinated RGPO/VGPO.

Establishing Cyberspace Sovereignty

International norms governing appropriate conduct in cyberspace are immature, leaving politicians, diplomats, and military authorities to grapple with the challenges of defending against and executing hostilities in cyberspace. Cyberspace is unlike the traditional physical domains where actions occur at specific geographic places and times. Rules governing conduct in the traditional domains emerged over centuries and share a common understanding of sovereignty that helps establish and justify the use of force. In cyberspace, sovereignty is a more abstract notion because the geographic boundaries are often difficult to define as data and applications increasingly reside in a virtual, global “cloud.” This paper proposes a construct for establishing sovereignty in cyberspace by studying similarities between space and cyberspace. The characteristics of the space domain challenged traditional notions of sovereignty based on geography. As nations deployed space-based capabilities, the concept of sovereignty needed to mature to deal with the physical realities of space. Sovereignty is defined, and general requirements for claiming sovereignty are presented. The evolution of sovereignty in space is then discussed, followed by a construct for how sovereignty could be defined in cyberspace. The paper also reviews U.S. civil policy and military doctrine and discusses how these documents offer insights into the U.S. approach to asserting its claims within these domains. It concludes by examining an emerging trend where nations not only seek to establish sovereign claims over the architectural aspects of cyberspace, but also the information that flows over it. Establishing Cyberspace Sovereignty

Classification of canonical scattering through sub-band analysis

The spectrum parted linked image test (SPLIT) algorithm was experimentally shown to estimate frequency-dependency of dominant scattering centers through sub-band analysis. Based on its demonstrated potential for classifying canonical scatterers, a theoretical model of the SPLIT algorithm is presented in this paper. Terms are defined, procedures are detailed, and a metric for total least squares model fitting is developed. In addition, the paper addresses multiple observations, measures of confidence, sidelobe interference and sensitivity to bandwidth and noise. Finally, it is described how the one-dimensional (1D) SPLIT algorithm can be extended for use with 2D and 3D imaging.

Waveform optimization for electronic countermeasure technique generation

Recent work on electronic countermeasure (ECM) technique generation employed genetic algorithm optimization methods to define simple range-gate pull-off waveforms against a generic range-tracking radar simulation. This automated approach has potential to greatly reduce technique development time which is traditionally prolonged by manual experimentation. However, it also inspires a more generalized approach to optimization with hardware-in-the-loop configurations. This work investigates and develops the underlying mathematical and empirical framework for using optimization algorithms for hardware-in-the-loop simulation and testing. Unlike other reported radar/ECM optimization simulations, this approach uses a cost function library and scoring definition to separate simulation from the optimization algorithm, and is easily adapted to hardware-in-the-loop testing. In addition, effects from electromagnetic scattering and radar receiver processing may be measured, removing the need for completely defined objective functions. Finally, this approach nicely generalizes to multiple simultaneous cost function optimization. The method is demonstrated using the wellknown range-gate pull-off technique, but is adaptable to other ECM techniques. Future efforts will investigate specific optimization algorithms for the multi-objective problem.

Multistatic measurements in a controlled laboratory environment

In recent years, a novel mathematical framework for analyzing and designing multistatic radar systems has been proposed. It was argued through numerous simulation examples that multistatic radar system performances can be significantly improved by shaping the multistatic ambiguity function. Based on this framework, rules for waveform selection, sensor positioning and adequate weighting of different receivers have been developed. In this work, we present multistatic measurements obtained in a controlled laboratory environment to support some of these recent findings and conclusions. The experimental setup consists of a Lab-Volt™ radar system operating at X-band, Tektronix arbitrary waveform generator and Tektronix digital oscilloscope. Multistatic point target radar measurements for different system configurations are analyzed.