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SAR ambiguous range suppression.

Description: Pulsed Radar systems suffer range ambiguities, that is, echoes from pulses transmitted at different times arrive at the receiver simultaneously. Conventional mitigation techniques are not always adequate. However, pulse modulation schemes exist that allow separation of ambiguous ranges in Doppler space, allowing easy filtering of problematic ambiguous ranges.
Date: September 1, 2006
Creator: Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department

Ship dynamics for maritime ISAR imaging.

Description: Demand is increasing for imaging ships at sea. Conventional SAR fails because the ships are usually in motion, both with a forward velocity, and other linear and angular motions that accompany sea travel. Because the target itself is moving, this becomes an Inverse- SAR, or ISAR problem. Developing useful ISAR techniques and algorithms is considerably aided by first understanding the nature and characteristics of ship motion. Consequently, a brief study of some principles of naval architecture sheds useful light on this problem. We attempt to do so here. Ship motions are analyzed for their impact on range-Doppler imaging using Inverse Synthetic Aperture Radar (ISAR). A framework for analysis is developed, and limitations of simple ISAR systems are discussed.
Date: February 1, 2008
Creator: Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department

SAR impulse response with residual chirps.

Description: A Linear Frequency-Modulated (LFM) chirp is a function with unit amplitude and quadratic phase characteristic. In a focused Synthetic Aperture Radar (SAR) image, a residual chirp is undesired for targets of interest, as it coarsens the manifested resolution. However, for undesired spurious signals, a residual chirp is often advantageous because it spreads the energy and thereby diminishes its peak value. In either case, a good understanding of the effects of a residual LFM chirp on a SAR Impulse Response (IPR) is required to facilitate system analysis and design. This report presents an analysis of the effects of a residual chirp on the IPR. As reference, there is a rich body of publications on various aspects of LFM chirps. A quick search reveals a plethora of articles, going back to the early 1950s. We mention here purely as trivia one of the earlier analysis papers on this waveform by Klauder, et al.
Date: June 1, 2009
Creator: Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department

Performance limits for Synthetic Aperture Radar.

Description: The performance of a Synthetic Aperture Radar (SAR) system depends on a variety of factors, many which are interdependent in some manner. It is often difficult to ''get your arms around'' the problem of ascertaining achievable performance limits, and yet those limits exist and are dictated by physics, no matter how bright the engineer tasked to generate a system design. This report identifies and explores those limits, and how they depend on hardware system parameters and environmental conditions. Ultimately, this leads to a characterization of parameters that offer optimum performance for the overall SAR system. For example, there are definite optimum frequency bands that depend on weather conditions and range, and minimum radar PRF for a fixed real antenna aperture dimension is independent of frequency. While the information herein is not new to the literature, its collection into a single report hopes to offer some value in reducing the ''seek time''.
Date: February 1, 2006
Creator: Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department

Radar cross section of triangular trihedral reflector with extended bottom plate.

Description: Trihedral corner reflectors are the preferred canonical target for SAR performance evaluation for many radar development programs. The conventional trihedrals have problems with substantially reduced Radar Cross Section (RCS) at low grazing angles, unless they are tilted forward, but in which case other problems arise. Consequently there is a need for better low grazing angle performance for trihedrals. This is facilitated by extending the bottom plate. A relevant analysis of RCS for an infinite ground plate is presented. Practical aspects are also discussed.
Date: May 1, 2009
Creator: Brock, Billy C. & Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department

IFP V4.0:a polar-reformatting image formation processor for synthetic aperture radar.

Description: IFP V4.0 is the fourth generation of an extraordinarily powerful and flexible image formation processor for spotlight mode synthetic aperture radar. It has been successfully utilized in processing phase histories from numerous radars and has been instrumental in the development of many new capabilities for spotlight mode SAR. This document provides a brief history of the development of IFP, a full exposition of the signal processing steps involved, and a short user's manual for the software implementing this latest iteration.
Date: September 1, 2005
Creator: Eichel, Paul H.
Partner: UNT Libraries Government Documents Department

SAR processing with non-linear FM chirp waveforms.

Description: Nonlinear FM (NLFM) waveforms offer a radar matched filter output with inherently low range sidelobes. This yields a 1-2 dB advantage in Signal-to-Noise Ratio over the output of a Linear FM (LFM) waveform with equivalent sidelobe filtering. This report presents details of processing NLFM waveforms in both range and Doppler dimensions, with special emphasis on compensating intra-pulse Doppler, often cited as a weakness of NLFM waveforms.
Date: December 1, 2006
Creator: Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department

Folded Compact Range Development and Coherent Change Detection Measurement Project

Description: A novel, folded compact range configuration has been developed at the Sandia National Laboratories compact range antenna and radar cross section measurement facility, operated by the Radar/Antenna Department 2343, as a means of performing indoor, environmentally-controlled, far-field simulations of synthetic aperture radar (SAR) coherent change detection (CCD) measurements. This report describes the development of the folded compact range configuration, as well as the initial set of coherent change detection measurements made with the system. These measurements have been highly successful, and have demonstrated the viability of the folded compact range concept in simulating SAR CCD measurements. It is felt that follow-on measurements have the potential of contributing significantly to the body of knowledge available to the scientific community involved in CCD image generation and processing, and that this tool will be a significant aid in the research and development of change detection methodologies.
Date: March 1, 1995
Creator: Sorensen, K.W.
Partner: UNT Libraries Government Documents Department

Imaging radar for bridge deck inspection

Description: Lawrence Livermore National Laboratory (LLNL)l is developing a prototype imaging radar for inspecting steel reinforced concrete bridge decks. The system is designed to acquire Synthetic Aperture Radar (SAR) data and provide high-resolution images of internal structure, flaws, and defects enabling bridge inspectors to nondestructively evaluate and characterize bridge deck condition. Concrete delamination resulting from corrosion of steel reinforcing bars (rebars) is an important structural defect that the system is designed to detect. The prototype system uses arrays of compact, low-cost Micropower Impulse Radar (MIR) modules, supported by appropriate data acquisition and storage subsystems, to generate and collect the radar data, and unique imaging codes to reconstruct images of bridge deck internals. In this paper, we provide an overview of the prototype system concept, discuss its expected performance, and present recent experimental results showing the capability of this approach to detect thin delamination simulations embedded in concrete.
Date: April 13, 1995
Creator: Warhus, J.; Mast, J. & Nelson, S.
Partner: UNT Libraries Government Documents Department

A cost-effective adverse-weather precision guidance system

Description: This SAND report documents the results of an LDRD project undertaken to study the accuracy of terrain-aided navigation coupled with highly accurate topographic maps. A revolutionary new mapping technology, interferometric synthetic aperture radar (IFSAR), has the ability to make terrain maps of extremely high accuracy and spatial resolution, more than an order of magnitude better than currently available DMA map products. Using a laser altimeter and the Sandia Labs Twin Otter Radar Testbed, fix accuracies of less than 3 meters CEP were obtained over urban and natural terrain regions.
Date: August 1, 1995
Creator: Fellerhoff, R. & Burgett, S.
Partner: UNT Libraries Government Documents Department

Wavefront curvature limitations and compensation to polar format processing for synthetic aperture radar images.

Description: Limitations on focused scene size for the Polar Format Algorithm (PFA) for Synthetic Aperture Radar (SAR) image formation are derived. A post processing filtering technique for compensating the spatially variant blurring in the image is examined. Modifications to this technique to enhance its robustness are proposed.
Date: January 1, 2006
Creator: Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department

Estimating IMU heading error from SAR images.

Description: Angular orientation errors of the real antenna for Synthetic Aperture Radar (SAR) will manifest as undesired illumination gradients in SAR images. These gradients can be measured, and the pointing error can be calculated. This can be done for single images, but done more robustly using multi-image methods. Several methods are provided in this report. The pointing error can then be fed back to the navigation Kalman filter to correct for problematic heading (yaw) error drift. This can mitigate the need for uncomfortable and undesired IMU alignment maneuvers such as S-turns.
Date: March 1, 2009
Creator: Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department

New formulation for interferometric synthetic aperture radar for terrain mapping

Description: The subject of interferometric synthetic aperture radar (IFSAR) for high-accuracy terrain elevation mapping continues to gain importance in the arena of radar signal processing. Applications to problems in precision terrain-aided guidance and automatic target recognition, as well as a variety of civil applications, are being studied by a number of researchers. Not unlike many other areas of SAR processing, the subject of IFSAR can at first glance appear to be somewhat mysterious. In this paper we show how the mathematics of IFSAR for terrain elevation mapping using a pair of spotlight mode SAR collections can be derived in a very straightforward manner. Here, we employ an approach that relies entirely on three-dimensional Fourier transforms, and utilizes no reference to range equations or Doppler concepts. The result is a simplified explanation of the fundamentals of interferometry, including an easily-seen link between image domain phase difference and terrain elevation height. The derivation builds upon previous work by the authors in which a framework for spotlight mode SAR image formation based on an analogy to three-dimensional computerized axial tomography (CAT) was developed. After outlining the major steps in the mathematics, we show how a computer simulator which utilizes three-dimensional Fourier transforms can be constructed that demonstrates all of the major aspects of IFSAR from spotlight mode collections.
Date: April 1, 1994
Creator: Jakowatz, C. V. Jr.; Wahl, D. E.; Eichel, P. H. & Thompson, P. A.
Partner: UNT Libraries Government Documents Department

New approach to strip-map SAR autofocus

Description: Means for removing phase errors induced in spotlight mode synthetic aperture radar (SAR) imagery are now well-established. The Phase Gradient Autofocus (PGA) algorithm has been shown to be robust over a wide range of spotlight mode imagery and phase error functions. These phase errors could have their origin either in uncompensated platform motion or random propagation delays incurred, for example, from tropospheric turbulence. The PGA technique, however, cannot be directly applied to imagery formed in the conventional strip-mapping mode. In this paper we show that if the fundamental ideas of PGA are modified in an appropriate way, the phase errors in strip-map imagery can be effectively estimated and compensated.
Date: May 1, 1994
Creator: Wahl, D.; Jakowatz, C.; Thompson, P. & Ghiglia, D.
Partner: UNT Libraries Government Documents Department

ASAP progress and expenditure report for the month of December 1--31, 1995. Joint UK/US radar program

Description: The RAR/SAR is a high-priority radar system for the joint US/UK Program. Based on previous experiment results and coordination with the UK, specifications needed for future radar experiments were identified as follows: dual polarimetric (HH and VV) with medium to high resolution in SAR mode. Secondary airborne installation requirements included; high power (circa 10kw) and SLIER capability to emulate Tupelev-134 type system; initially x-band but easily extendible to other frequencies. In FY96 we intended to enhance the radar system`s capabilities by providing a second polarization (VV), spotlight imaging mode, extended frequency of operation to include S- band, increase power, and interface to an existing infrared sensor. Short term objectives are: continue to evaluate and characterize the radar system; upgrade navigation and real-time processing capability to refine motion compensation; upgrade to dual polarimetry (add VV); and develop a ``spotlight`` mode capability. Accomplishments this reporting period: design specifications for the SAR system polarimetric upgrade are complete. The upgrade is ready to begin the procurement cycle when funds become available. System characterization is one of the highest priority tasks for the SAR. Although the radar is dedicated for our use, Hughes is waiting for contract funding before allowing us access to the hardware
Date: January 19, 1996
Creator: Twogood, R.E.; Brase, J.M.; Chambers, D.H.; Mantrom, D.D.; Miller, M.G.; Newman, M.J. et al.
Partner: UNT Libraries Government Documents Department

Determination of absolute interferometric phase using the beam-amplitude ratio technique

Description: Determination of the absolute phase difference (i.e., not modulo 2{pi}) is a key problem in interferometric synthetic aperture radar (IFSAR) for topographic mapping. One way of solving this problem requires use of a technique different from the basic interferometry to resolve a `coarse` angle measurement that lies within the IFSAR ambiguity angle. The method investigated in this paper involves taking advantage of the difference in the amplitude ratio versus elevation angle that occurs when the elevation beams of the two IFSAR antennas are pointed in slightly different directions. The performance of the technique is a function of the angular separation of the two beams, the elevation beamwidth, and the symmetry of the two beam-amplitude patterns. The performance required of the technique is set by the ambiguity angle of the interferometer. This paper presents an analysis of the beam-amplitude ratio technique and shows experimental results.
Date: March 1, 1996
Creator: Bickel, D.L. & Hensley, W.H.
Partner: UNT Libraries Government Documents Department

Lossless compression of synthetic aperture radar images

Description: Synthetic Aperture Radar (SAR) has been proven an effective sensor in a wide variety of applications. Many of these uses require transmission and/or processing of the image data in a lossless manner. With the current state of SAR technology, the amount of data contained in a single image may be massive, whether the application requires the entire complex image or magnitude data only. In either case, some type of compression may be required to losslessly transmit this data in a given bandwidth or store it in a reasonable volume. This paper provides the results of applying several lossless compression schemes to SAR imagery.
Date: February 1, 1996
Creator: Ives, R.W.; Magotra, N. & Mandyam, G.D.
Partner: UNT Libraries Government Documents Department

COPE Coastal ocean probe experiment Northern Oregon Coast 14-16 September 1995: Test Operations Report summary of Lawrence Livermore National Laboratory activities

Description: Operations involving Lawrence Livermore National Laboratory (LLNL) assets associated with a field experiment named COPE (Coastal Ocean Probe Experiment) are described. The lead organization responsible for the planning and conduct of COPE is NOAA/ETL headquartered in Boulder, Colorado. This experiment was conducted off the coast of Northern Oregon during September-October 1995. The primary measurements involve radars and other imaging microwave sensors imaging surface effects associated with natural internal waves which are abundant off the Oregon coast in the late summer and early fall. In-water, surface, and above- water environmental sensors were fielded by ETL and their contractors on the FLIP platform moored 13 miles offshore and elsewhere to characterize the environmental conditions and help interpret various features in the imagery. LLNL`s Imaging and Detection Program has taken advantage of this unique site and suite of ground-truth measurements to collect radar image data over a three-day period (14-16 September 1995) with our Airborne Experimental Test Bed (AETB) and its X-band, HH-polarization synthetic aperture radar (SAR) as a piggyback to the primary COPE data collection. This report documents test operations during this three-day data collection involving the AETB/SAR from a LLNL perspective. A total of 42 SAR images were collected at grazing angles of 8{degrees}, 20{degrees}, and 45{degrees}. From all indications during data collection, data quality appears good for about 75 percent of the passes. Strong internal waves were observed each day in calm to light wind conditions. ETL`s hillside dual-polarization X-band and Ka-band real aperture radars recorded data simultaneous with the AETB SAR. The presence of other airborne platforms and low cloud cover limited the AETB aircraft`s ability to operate at low altitude. Limited sea-truth data was collected onboard FLIP.
Date: October 1, 1995
Creator: Mantrom, D.D. & Miller, M.G.
Partner: UNT Libraries Government Documents Department

MiniSAR composite gimbal arm development.

Description: An exploratory effort in the application of carbon epoxy composite structural materials to a multi-axis gimbal arm design is described. An existing design in aluminum was used as a baseline for a functionally equivalent redesigned outer gimbal arm using a carbon epoxy composite material. The existing arm was analyzed using finite element techniques to characterize performance in terms of strength, stiffness, and weight. A new design was virtually prototyped. using the same tools to produce a design with similar stiffness and strength, but reduced overall weight, than the original arm. The new design was prototyped using Rapid Prototyping technology, which was subsequently used to produce molds for fabricating the carbon epoxy composite parts. The design tools, process, and results are discussed.
Date: January 1, 2005
Creator: Klarer, Paul Richard & Winscott, Mark (Orion International, Albuquerque, NM)
Partner: UNT Libraries Government Documents Department

Anatomy of a SAR impulse response.

Description: A principal measure of Synthetic Aperture Radar (SAR) image quality is the manifestation in the SAR image of a spatial impulse, that is, the SAR's Impulse Response (IPR). IPR requirements direct certain design decisions in a SAR. Anomalies in the IPR can point to specific anomalous behavior in the radar's hardware and/or software.
Date: August 1, 2007
Creator: Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department

Reflectors for SAR performance testing.

Description: Synthetic Aperture Radar (SAR) performance testing and estimation is facilitated by observing the system response to known target scene elements. Trihedral corner reflectors and other canonical targets play an important role because their Radar Cross Section (RCS) can be calculated analytically. However, reflector orientation and the proximity of the ground and mounting structures can significantly impact the accuracy and precision with which measurements can be made. These issues are examined in this report.
Date: January 1, 2008
Creator: Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department

SAR polar format implementation with MATLAB.

Description: Traditional polar format image formation for Synthetic Aperture Radar (SAR) requires a large amount of processing power and memory in order to accomplish in real-time. These requirements can thus eliminate the possible usage of interpreted language environments such as MATLAB. However, with trapezoidal aperture phase history collection and changes to the traditional polar format algorithm, certain optimizations make MATLAB a possible tool for image formation. Thus, this document's purpose is two-fold. The first outlines a change to the existing Polar Format MATLAB implementation utilizing the Chirp Z-Transform that improves performance and memory usage achieving near realtime results for smaller apertures. The second is the addition of two new possible image formation options that perform a more traditional interpolation style image formation. These options allow the continued exploration of possible interpolation methods for image formation and some preliminary results comparing image quality are given.
Date: November 1, 2005
Creator: Martin, Grant D. & Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department