David A. Garren

Theory of Two-Dimensional Signature Morphology for Arbitrarily Moving Surface Targets in Squinted Spotlight Synthetic Aperture Radar

This paper develops analytic equations for predicting the smear signature morphology due to surface targets having arbitrary motion within squinted spotlight synthetic aperture radar (SAR) imagery. A power-series expansion of the subaperture phase history data is applied to compute a generic expression for the down-range and cross-range components of the predicted central 2-D contour of mover signatures, including the cross-range offset. In addition, the current analysis generates an analytic approximation for the 2-D impulse response (IPR) of surface moving target signatures within subaperture images. This investigation reveals that the summation of a large number of nonoverlapping IPRs yields an excellent reproduction of the target signature, including smear width and self-interference effects, as compared with standard image formation using simulated radar data. Thus, the analytics derived herein can provide an effective methodology for understanding the shape, extent, location, width, and interference effects of smears due to arbitrarily moving surface targets for squinted spotlight SAR.

Signature Morphology Effects of Squint Angle for Arbitrarily Moving Surface Targets in Spotlight Synthetic Aperture Radar

This investigation examines the phenomenology effects of the squint angle on the morphology of moving target smears in spotlight synthetic aperture radar (SAR). This analysis includes both the smears resulting from standard image formation applied to simulated radar measurements as well as the theoretical predictions for the central contours of the signatures. In particular, this paper generates the down-range and cross-range components of the predicted central 2-D contours of mover signatures, including the locations of the cross-range offsets. The analytics for squinted geometry include additional contributions in the signature contour equations that do not arise for the case of broadside imaging. These terms can affect the overall contour morphology, particularly in terms of shape and extent. Numerous examples are presented to demonstrate that the signature prediction equations yield excellent agreement with standard image formation with simulated radar data. Therefore, this analysis can provide an effective tool in predicting the shape, extent, and location of smears due to arbitrarily moving surface targets for squinted spotlight SAR.

Signatures of braking surface targets in spotlight synthetic aperture radar

This paper examines the signature characteristics in spotlight synthetic aperture radar (SAR) image data for surface targets that are executing braking maneuvers during the SAR collection. This analysis considers the special case in which the radar sensor is assumed to move with constant speed and heading on a level flight path with broadside imaging geometry. The analysis concentrates on the target migration effects in which the moving target smear exhibits some defocus in the range direction, although much smaller in magnitude than the smearing in the radar crossrange direction. This paper focuses on the case of a target that executes a rapid speed transition by decreasing its speed within the synthetic aperture. The SAR simulations are shown to give signatures that are in agreement with the predicted shapes.

Signature predictions of surface targets undergoing turning maneuvers in spotlight synthetic aperture radar imagery

This paper investigates methodologies for predicting the smear signatures in broadside spotlight synthetic aperture radar imagery collections due to surface targets that are undergoing turning maneuvers. This analysis examines the case of broadside geometry wherein the radar moves with constant speed and heading on a level flight path. This investigation concentrates moving target smear issues that yield some defocus in the range direction, although much smaller in magnitude than the motion induced smearing in the radar cross-range direction. This paper focuses on the case of a target that executes a turning maneuver during the SAR collection interval. The SAR simulations are shown to give excellent agreement between the moving target signatures and the predicted shapes of the central contours.

Target migration path morphology of moving targets in spotlight SAR

This paper examines the signature characteristics of moving targets in spotlight synthetic aperture radar (SAR) image data. This analysis considers the special case in which the radar sensor is assumed to move with constant speed and heading on a level flight path with broadside imaging geometry. It is shown that the resulting defocused smear signature in the spotlight SAR image exhibits range migration effects, as has been shown previously for strip map SAR analysis. In particular, cases of uniform target motion exhibit simply curved range migration paths, whereas non-uniform target motion can cause complicated smear shapes.

Use of P3-coded transmission waveforms to generate synthetic aperture radar images

This paper develops methods for using low probability of intercept (LPI) transmission waveforms in order to generate synthetic aperture radar (SAR) imagery. This analysis considers a specific transmission waveform based upon P3 codes in order to give phase shift keying (PSK) modulation. A matched correlation receiver is used to form SAR imagery corresponding to the transmitted P3-modulated waveforms. This analysis demonstrates the ability to generate SAR images based upon simulated radar measurements collected by a notional radar platform that can transmit and receive P3 waveforms. This work analyzes the resulting spotlight-mode SAR images that are generated using the P3 transmission waveforms.

Phenomenology of low probability of intercept synthetic aperture radar via Frank codes

This paper investigates techniques for using low probability of intercept (LPI) modulation techniques for forming synthetic aperture radar (SAR) imagery. This analysis considers a specific waveform type based upon Frank codes in providing for the LPI capability via phase shift keying (PSK) modulation. A correlation receiver that is matched to the transmitted waveform is utilized to generate a set of SAR data. This analysis demonstrates the ability to form SAR images based upon simulated radar measurements collected by a notional radar sensor that has ability to transmit and receive Frank-coded waveforms and to form SAR images based upon the results of a correlation receiver. Spotlight-mode SAR images are generated using the Frank-coded waveforms and their properties are analyzed and discussed.

A spatiotemporal clustering approach to maritime domain awareness

Spatiotemporal clustering is the process of grouping objects based on both their spatial and temporal similarity. This approach is useful when considering the distance between objects and how that distance changes through time. Spatiotemporal clustering analysis is applied to the maritime domain in this paper, specifically to a defined area of water, during a period of time, in order to gain behavioral knowledge of vessel interactions and provide the opportunity to screen such interactions for further investigation. The proposed spatiotemporal clustering algorithm spatially clusters vessels in the water space using k-means clustering analysis, kinematically refines the clusters based on the similarity of vessel headings, speeds and the distance between them, and temporally analyzes the continuity of membership of the kinematic clusters through time to determine which clusters are moving. The algorithm is implemented in the MATLAB programming environment, verified with a synthetic data scenario, and validated with two real-world datasets.

SAR Ground Plane Mover Signatures for Nonzero Radar Ascent

Recent spotlight synthetic aperture radar analyses predict the two-dimensional range migration signature smears induced by targets with arbitrary motion in the ground plane. These investigations were limited to a constant-velocity radar motion with level flight path. The current correspondence removes this constraint by including the radar trajectory ascent angle.

Signature predictions of surface targets undergoing braking maneuvers in squinted spotlight synthetic aperture radar imagery

This paper investigates methodologies for predicting the smear signatures in squinted spotlight synthetic aperture radar (SAR) imagery collections due to surface targets that are undergoing braking maneuvers. Previous analysis considered the case of broadside collection geometries. Analytic computation of a power series expansion is used to compute a generic expression for the down-range and cross-range components of the predicted mover signature. In addition, recent analysis presents capabilities for predicting the full signature shape, including the smear width and interference effects. The current investigations focuses on the effects of squinted collection geometries upon braking targets signatures.