Sonar and radar SAR processing for parking lot detection

In this paper, SAR processing algorithms for automotive applications are presented and illustrated on data from non-trivial test scenes. The chosen application is parking lot detection. Laboratory results obtained with a teaching sonar experiment emphasize the resolution improvement introduced with range-Doppler SAR processing. A similar improvement is then confirmed through full scale measurements performed with an automotive radar prototype operating at 77GHz in very close range conditions, typical of parking lot detection. The collected data allows a performance comparison between different SAR processing algorithms for realistic targets

Target Motion Estimation Techniques in Single-Channel SAR

—Synthetic Aperture Radar (SAR) systems are versatile, high-resolution radar imagers useful for providing detailed intelligence, surveillance, and reconnaissance, especially when atmospheric conditions are non-ideal for optical imagers. However, targets in SAR images are smeared when they are moving. Along-track interferometry is a commonly-used method for extracting the motion parameters of moving targets but requires a dualaperture SAR system, which may be power- size- or cost prohibitive. This paper presents a method of estimating target motion parameters in single-channel SAR data given geometric target motion constraints. This estimation method includes an initial estimate, computation of the SAR ambiguity function, and application of the target motion constraints

Wide-Angle Multistatic Synthetic Aperture Radar: Focused Image Formation and Aliasing Artifact Mitigation

Traditional monostatic Synthetic Aperture Radar (SAR) platforms force the user to choose between two image types: larger, low resolution images or smaller, high resolution images. Switching to a Wide-Angle Multistatic Synthetic Aperture Radar (WAM-SAR) approach allows formation of large high-resolution images. Unfortunately, WAM-SAR suffers from two significant implementation problems. First, wavefront curvature effects, non-linear flight paths, and warped ground planes lead to image defocusing with traditional SAR processing methods. A new 3-D monostatic/bistatic image formation routine solves the defocusing problem, correcting for all relevant wide-angle effects. Inverse SAR (ISAR) imagery from a Radar Cross Section (RCS) chamber validates this approach. The second implementation problem stems from the large Doppler spread in the wide-angle scene, leading to severe aliasing problems. This research effort develops a new anti-aliasing technique using randomized Stepped-Frequency (SF) waveforms to form Doppler filter nulls coinciding with aliasing artifact locations. Both simulation and laboratory results demonstrate effective performance, eliminating more than 99% of the aliased energy

Advanced digital SAR processing study

A highly programmable, land based, real time synthetic aperture radar (SAR) processor requiring a processed pixel rate of 2.75 MHz or more in a four look system was designed. Variations in range and azimuth compression, number of looks, range swath, range migration and SR mode were specified. Alternative range and azimuth processing algorithms were examined in conjunction with projected integrated circuit, digital architecture, and software technologies. The advaced digital SAR processor (ADSP) employs an FFT convolver algorithm for both range and azimuth processing in a parallel architecture configuration. Algorithm performace comparisons, design system design, implementation tradeoffs and the results of a supporting survey of integrated circuit and digital architecture technologies are reported. Cost tradeoffs and projections with alternate implementation plans are presented

Convex Model-Based Synthetic Aperture Radar Processing

The use of radar often conjures up images of small blobs on a screen. But current synthetic aperture radar (SAR) systems are able to generate near-optical quality images with amazing benefits compared to optical sensors. These SAR sensors work in all weather conditions, day or night, and provide many advanced capabilities to detect and identify targets of interest. These amazing abilities have made SAR sensors a work-horse in remote sensing, and military applications. SAR sensors are ranging instruments that operate in a 3D environment, but unfortunately the results and interpretation of SAR images have traditionally been done in 2D. Three-dimensional SAR images could provide improved target detection and identification along with improved scene interpretability. As technology has increased, particularly regarding our ability to solve difficult optimization problems, the 3D SAR reconstruction problem has gathered more interest. This dissertation provides the SAR and mathematical background required to pose a SAR 3D reconstruction problem. The problem is posed in a way that allows prior knowledge about the target of interest to be integrated into the optimization problem when known. The developed model is demonstrated on simulated data initially in order to illustrate critical concepts in the development. Then once comprehension is achieved the processing is applied to actual SAR data. The 3D results are contrasted against the current gold- standard. The results are shown as 3D images demonstrating the improvement regarding scene interpretability that this approach provides

Generalized SAR Processing and Motion Compensation

Application speci c algorithms for processing SAR data have been researched for many years, but a general theory is not well de ned. This paper presents a generalized way to look at SAR processing and uses the principles leared to develop an improved motion compensation method. The non-ideal motion of a SAR platform results in degraded image quality, but for known motion, corrections can be made. Traditional motion compensation requires a computationally costly interpolation step to correct translational motion greater than a single range bin. This paper presents an ef cient new motion compensation algorithm that corrects this range shift without interpolation. The new method is veri ed with simulated SAR data and data collected with the NuSAR

Motion-compensation for complementary-coded medical ultrasonic imaging

Ultrasound is a well-established tool for medical imaging. It is non-invasive and relatively inexpensive, but the severe attenuation caused by propagation through tissue limits its effectiveness for deep imaging. In recent years, the ready availability of fast, inexpensive computer hardware has facilitated the adoption of signal coding and compression techniques to counteract the effects of attenuation. Despite widespread investigation of the topic, published opinions vary as to the relative suitability of discrete-phase-modulated and frequency-modulated (or continuous-phase-modulated) signals for ultrasonic imaging applications. This thesis compares the performance of discrete binary-phase coded pulses to that of frequency-modulated pulses at the higher imaging frequencies at which the effects of attenuation are most severe. The performance of linear and non-linear frequency modulated pulses with optimal side-lobe characteristics is compared to that of complementary binary-phase coded pulses by simulation and experiment. Binary-phase coded pulses are shown to be more robust to the affects of attenuation and non-ideal transducers. The comparatively poor performance of frequency-modulated pulses is explained in terms of the spectral characteristics of the signals and filters required to reduce side-lobes to levels acceptable for imaging purposes. In theory, complementary code sets like bi-phase Golay pairs offer optimum side-lobe performance at the expense of a reduction in frame rate. In practice, misalignment caused by motion in the medium can have a severe impact on imaging performance. A novel motioncompensated imaging algorithm designed to reduce the occurrence of motion artefacts and eliminate the reduction in frame-rate associated with complementary-coding is presented. This is initially applied to conventional sequential-scan B-mode imaging then adapted for use in synthetic aperture B-mode imaging. Simulation results are presented comparing the performance of the motion-compensated sequential-scan and synthetic aperture systems with that of simulated systems using uncoded and frequency-modulated excitation pulses

Frequency-modulated continuous-wave synthetic-aperture radar: improvements in signal processing

With the advance of solid state devices, frequency-modulated continuous-wave (FMCW) designs have recently been used in synthetic-aperture radar (SAR) to decrease cost, size, weight and power consumption, making it deployable on smaller mobile plat-forms, including small (< 25 kg) unmanned aerial vehicle(s) (UAV). To foster its mobile uses, several SAR capabilities were studied: moving target indication (MTI) for increased situational awareness, bistatic operation, e.g. in UAV formation flights, for increased range, and signal processing algorithms for faster real-time performance. Most off-the-shelf SAR systems for small mobile platforms are commercial proprie-tary and/or military (ITAR, International Trades in Arms Regulations) restricted. As such, it necessitated the design and build of a prototype FMCW SAR system at the early stage to serve as a research tool. This enabled unrestricted hardware and software modifica-tions and experimentation. A model to analyze the triangularly modulated (TM) linear frequency modulated (LFM) waveform as one signal was established and used to develop a MTI algorithm which is effective for slow moving targets detection. Experimental field data collected by the prototyped FMCW SAR was then used to validate and demonstrate the effectiveness of the proposed MTI method. A bistatic FMCW SAR model was next introduced: Bistatic configuration is a poten-tial technique to overcome the power leakage problem in monostatic FMCW SAR. By mounting the transmitter and receiver on spatially separate mobile (UAV) platforms in formation deployment, the operation range of a bistatic FMCW SAR can be significantly improved. The proposed approximation algorithm established a signal model for bistatic FMCW SAR by using the Fresnel approximation. This model allows the existing signal processing algorithms to be used in bistatic FMCW SAR image generation without sig-nificant modification simplifying bistatic FMCW SAR signal processing. The proposed range migration algorithm is a versatile and efficient FMCW SAR sig-nal processing algorithm which requires less memory and computational load than the traditional RMA. This imaging algorithm can be employed for real-time image genera-tion by the FMCW SAR system on mobile platforms. Simulation results verified the pro-posed spectral model and experimental data demonstrated the effectiveness of the modi-fied RMA

Interferometric Synthetic Aperture Sonar Signal Processing for Autonomous Underwater Vehicles Operating Shallow Water

The goal of the research was to develop best practices for image signal processing method for InSAS systems for bathymetric height determination. Improvements over existing techniques comes from the fusion of Chirp-Scaling a phase preserving beamforming techniques to form a SAS image, an interferometric Vernier method to unwrap the phase; and confirming the direction of arrival with the MUltiple SIgnal Channel (MUSIC) estimation technique. The fusion of Chirp-Scaling, Vernier, and MUSIC lead to the stability in the bathymetric height measurement, and improvements in resolution. This method is computationally faster, and used less memory then existing techniques