Ronald Lipps

Time frequency signatures of micro-Doppler phenomenon for feature extraction

In this paper, we introduce the concept of micro-Doppler phenomenon. Micro-Doppler induced by mechanical vibrating or rotating of structures in a target is potentially useful for detection, classification and recognition of targets. While the Doppler frequency due to target body is constant, the micro-Doppler due to vibration or rotating structures of a target is a function of the dwell time. This time-varying Doppler signature in the time-frequency domain may provide further information for target detection, classification and recognition.

ISAR imaging of small craft with roll, pitch and yaw analysis

In this paper, we analyze the effect of roll, pitch and yaw rotations on inverse synthetic aperture radar (ISAR) imaging of small craft. An ideal ISAR image of a target with regular motion can be derived from the image projection plane and the radar line-of-sight (LOS) unit vector. Roll, pitch and yaw rotations can induce time-varying Doppler shifts that can be analyzed through the rotation matrix and the effective rotation vector. We use a commercial small craft ISAR data accompanied with roll, pitch and yaw data collected by the Trimble Tans Vector system with 4 GPS antennas to study the effect of rotational motion on ISAR imaging. For a target with regular motion, perturbations of roll and pitch motions may make for image blurring if conventional motion compensation is used. In this case, advanced imaging algorithms, such as the polar reformatting algorithm, that compensate the perturbations may improve the image.

Radar imaging of ground moving targets

We analyze the effect of target motion on synthetic aperture radar images and discuss how a multi-aperture radar can detect, focus and relocate moving targets in clutter. AN/APY-6 radar data is used for analyzing the radar imaging of ground moving targets. Some applications of the time-frequency transform to detect and focus moving targets are also discussed.

Advanced SAR GMTI techniques

Synthetic aperture radar (SAR) systems are designed to produce high quality imagery of a stationary target on the ground. These systems are not designed to handle moving targets and perform poorly in the areas of detecting and imaging moving targets. The paper presents advanced techniques developed to handle the detection and refocusing of moving targets for SAR systems.

Advanced synthetic aperture radar imaging and feature analysis

We review and discuss advanced algorithms for synthetic aperture radar image formation, the effect of motion perturbation on radar imaging, synthetic aperture radar imaging of ground moving targets, and micro-Doppler feature analysis.

Polar reformatting for ISAR imaging

Polar reformatting is a technique that has been developed and used extensively in spotlight SAR processing. The prerequisite for using this technique is to know the radars aspect angle, with respect to the target, for each pulse received by this radar. The key to using this technique for ISAR is to know the targets rotational motion which in most cases is unknown. This paper will present a practical motion geometry for the rotational motion of a target, based on a parameterized model. A technique, based on this rotation model, to determine the rotation parameters, using measurements from the radar data itself, will be presented. A practical realization of this technique, using simplifications to the motion model, will be discussed and the effects of this simplification will be described.

FOPEN SAR imaging of ground moving targets using rotational time-frequency-radon transforms

In this paper, we introduce the basic concept of the rotational Fourier transform, the bilinear rotational time-frequency transforms, and the Radon transform. Based on a certain model of radar returns from moving targets, we propose a method using a rotational time-frequency-Radon transform for synthetic aperture radar imaging of moving targets in foliage.

Analysis of radar dismount signatures via non-parametric and parametric methods

We present novel approaches to the analysis of radar dismount signatures that entail the characterization of the time-frequency (TF) structure of the received radar signal associated with the dismount gait by both non-parametric and parametric methods. We first introduce the concept of Gaussian g-Snakes in order to parametrically characterize the TF distribution of radar signals. In particular, we derive simple steepest descent equations that enable the estimation of the (locally) optimal g-Snake parameters for a given TF distribution. Furthermore the g-Snake modeling methodology gives us an objective unsupervised criterion from which to quantify the quality of the motion curve estimates that have been tracked from the TF data. We then formulate the non-parametric motion estimation for TF signals by a coupling of a simple partial tracking methodology in conjunction with boundary condition enforcement with regularity constraints. Finally we propose a coupling of the above non-parametric approach with g-Snake modeling that result in improved overall modeling of the given real and simulated radar TF data.

Velocity-ISAR: On the application of ISAR techniques to multichannel SAR imaging

The U.S. Naval Research Laboratory (NRL) Multichannel Synthetic Aperture Radar (MSAR) consists of multiple receive channels arranged along the flight direction and is unique in its ability to measure and correct for radial motion at each pixel in the scene. A well-known algorithm for performing MSAR imaging, and which have we applied for the first time to data captured by an airborne system, is the Velocity Synthetic Aperture Radar (VSAR) algorithm. VSAR calculates the distribution of Doppler radial velocities associated with each pixel and subsequently compensates for the velocities in order to combat motion blur. However, as we demonstrate in this paper, the VSAR algorithm does not fully exploit the special structure associated with the motion dynamics of rigid bodies (including translational and roll-pitch-yaw motions) in maritime conditions. To this end we propose the use of Inverse Synthetic Aperture Radar (ISAR) based motion compensation techniques-in conjunction with velocity filtering-as a means of accomplishing this objective for MSAR imaging. After describing the rudiments of the NRL MSAR system and the basics of ISAR processing, we subsequently proceed to describe our proposed Velocity-ISAR (VISAR) imaging algorithm. We demonstrate the performance of our VISAR algorithm by imaging boats captured by our airborne NRL MSAR system; and highlight its relative advantages over VSAR in imaging maritime targets.

Sparsity-based image reconstruction techniques for ISAR imaging

We present novel techniques for ISAR imaging via a Sparsity-based image reconstruction methodology. The latter offer a distinct advantage of Fourier based reconstruction techniques by offering the flexibility of using different basis functions to represent the underlying scene structure being imaged. We derive our ISAR algorithm in detail and present experimental results on real ISAR data showing its superiority over traditional Fourier based image reconstruction. We also demonstrate how our formulation of the ISAR imaging problem overcomes some of limitations associated previous approaches to CS (Compressive Sensing) based ISAR imaging in the literature.