The Fundamentals of Radar with Applications to Autonomous Vehicles

Radar systems can be extremely useful for applications in autonomous vehicles. This paper seeks to show how radar systems function and how they can apply to improve autonomous vehicles. First, the basics of radar systems are presented to introduce the basic terminology involved with radar. Then, the topic of phased arrays is presented because of their application to autonomous vehicles. The topic of digital signal processing is also discussed because of its importance for all modern radar systems. Finally, examples of radar systems based on the presented knowledge are discussed to illustrate the effectiveness of radar systems in autonomous vehicles

Application of Polarimetric GPR to detection of subsurface objects

Tohoku University佐藤源之課

Shape models and physical properties of asteroids

Despite the large amount of high quality data generated in recent space encounters with asteroids, the majority of our knowledge about these objects comes from ground based observations. Asteroids travelling in orbits that are potentially hazardous for the Earth form an especially interesting group to be studied. In order to predict their orbital evolution, it is necessary to investigate their physical properties. This paper briefly describes the data requirements and different techniques used to solve the lightcurve inversion problem. Although photometry is the most abundant type of observational data, models of asteroids can be obtained using various data types and techniques. We describe the potential of radar imaging and stellar occultation timings to be combined with disk-integrated photometry in order to reveal information about physical properties of asteroids.Comment: From Assessment and Mitigation of Asteroid Impact Hazards boo

Reduction of Vibration-Induced Artifacts in Synthetic Aperture Radar Imagery

Target vibrations introduce nonstationary phase modulation, which is termed the micro-Doppler effect, into returned synthetic aperture radar (SAR) signals. This causes artifacts, or ghost targets, which appear near vibrating targets in reconstructed SAR images. Recently, a vibration estimation method based on the discrete fractional Fourier transform (DFrFT) has been developed. This method is capable of estimating the instantaneous vibration accelerations and vibration frequencies. In this paper, a deghosting method for vibrating targets in SAR images is proposed. For single-component vibrations, this method first exploits the estimation results provided by the DFrFT-based vibration estimation method to reconstruct the instantaneous vibration displacements. A reference signal, whose phase is modulated by the estimated vibration displacements, is then synthesized to compensate for the vibration-induced phase modulation in returned SAR signals before forming the SAR image. The performance of the proposed method with respect to the signal-to-noise and signalto-clutter ratios is analyzed using simulations. Experimental results using the Lynx SAR system show a substantial reduction in ghosting caused by a 1.5-cm 0.8-Hz target vibration in a true SAR image

Three dimensional scattering center imaging techniques

Two methods to image scattering centers in 3-D are presented. The first method uses 2-D images generated from Inverse Synthetic Aperture Radar (ISAR) measurements taken by two vertically offset antennas. This technique is shown to provide accurate 3-D imaging capability which can be added to an existing ISAR measurement system, requiring only the addition of a second antenna. The second technique uses target impulse responses generated from wideband radar measurements from three slightly different offset antennas. This technique is shown to identify the dominant scattering centers on a target in nearly real time. The number of measurements required to image a target using this technique is very small relative to traditional imaging techniques

Ground-based ISAR imaging of cooperative and non-cooperative sea vessels with 3-D rotational motion

Includes bibliographical references (leaves 175-188).Inverse Synthetic Aperture Radar (ISAR) images of sea vessels are a rich source of information for radar cross section (RCS) measurement and ship classification. However, ISAR imaging of sea vessels is a challenging task because the 3-D rotational motion of such vessels often gives rise to blurring. Blurry ISAR images are not desirable because they lead to inaccurate parameter estimation, which reduces the probability of correct classification. The objective of this thesis is to explain how 3-D rotational motion causes blurring in ISAR imagery and to develop effective techniques for imaging cooperative and non-cooperative sea vessels for RCS measurement and ship-classification purposes respectively. Much research has been done to investigate the effect of 3-D rotational motion on an ISAR image under the assumption that an object's axis of rotation is constant over the coherent processing interval (CPI). In this thesis, a new quaternion-based system model is proposed to characterise the amount of blurring in an ISAR image when a sea vessel possesses 3-D rotational motion over a CPI. Simulations were done to characterise the migration of a scatterer through Doppler cells due to the time-varying nature of the Doppler generating axis of rotation. Simulation results with realistic 3-D rotational motion show substantial blurring in the cross-range dimension of the resulting ISAR image, and this blurring is attributed to the time-varying nature of the angle of the Doppler generating axis of rotation and the object's rotation rate over the CPI

Mitigation of Wide Angle Signal Interference in Terahertz Imaging Systems

abstract: The objective of this work is to design a low-profile compact Terahertz (THz) imaging system that can be installed in portable devices, unmanned aerial vehicles (UAVs), or CubeSats. Taking advantage of the rotational motion of these platforms, one can use linear antennas, such as leaky-wave antennas or linear phased arrays, to achieve fast image acquisition using simple RF front-end topologies. The proposed system relies on a novel image reconstructing technique that uses the principles of computerized tomography (Fourier-slice theorem). It can be implemented using a rotating antenna that produces a highly astigmatic fan-beam. In this work, the imaging system is composed of a linear phased antenna array with a highly directive beam pattern in the E-plane allowing for high spatial resolution imaging. However, the pattern is almost omnidirectional in the H-plane and extends beyond the required field-of-view (FOV). This is a major drawback as the scattered signals from any interferer outside the FOV will still be received by the imaging aperture and cause distortion in the reconstructed image. Also, fan beams exhibit significant distortion (curvature) when tilted at large angles, thus introducing errors in the final image due to its failure to achieve the assumed reconstructing algorithm. Therefore, a new design is proposed to alleviate these disadvantages. A 14×64 elements non-uniform array with an optimal flat-top pattern is designed with an iterative process using linear perturbation of a close starting pattern until the desired pattern is acquired. The principal advantage of this design is that it restricts the radiated/received power into the required FOV. As a result, a significant enhancement in the quality of images is achieved especially in the mitigation of the effect of any interferer outside the FOV. In this report, these two designs are presented and compared in terms of their imaging efficiency along with a series of numerical results verifying the proof of concept.Dissertation/ThesisMasters Thesis Electrical Engineering 201