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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

Generalized energy-aperture product limit for multi-beam and spotlight SARs

Description: The SAR energy-aperture product limit is extended to multi-beam SARS, Spotlight and moving spotlight SARS. This fundamental limit bounds the tradeoff between energy and antenna size. The kinematic relations between design variables such as platform speed, pulse repetition frequency, beam width and area rate are analyzed in a unified framework applicable to a wide variety of SARs including strip maps, spotlights, vermer arrays and multi-beam SARS, both scanning and swept-beam. Then the energy-aperture product limit is derived from the signal-to noise requirement and the kinematic constraints. The derivation clarifies impact of multiple beams and spotlighting on SAR performance.
Date: December 21, 1995
Creator: Karr, T.J.
Partner: UNT Libraries Government Documents Department

A comparison of spotlight synthetic aperture radar image formation techniques

Description: Spotlight synthetic aperture radar images can be formed from the complex phase history data using two main techniques: (1) polar-to-cartesian interpolation followed by two-dimensional inverse Fourier transform (2DFFT), and (2) convolution backprojection (CBP). CBP has been widely used to reconstruct medical images in computer aided tomography, and only recently has been applied to form synthetic aperture radar imagery. It is alleged that CBP yields higher quality images because (1) all the Fourier data are used and (2) the polar formatted data is used directly to form a 2D Cartesian image and therefore 2D interpolation is not required. This report compares the quality of images formed by CBP and several modified versions of the 2DFFT method. We show from an image quality point of view that CBP is equivalent to first windowing the phase history data and then interpolating to an exscribed rectangle. From a mathematical perspective, we should expect this conclusion since the same Fourier data are used to form the SAR image. We next address the issue of parallel implementation of each algorithm. We dispute previous claims that CBP is more readily parallelizable than the 2DFFT method. Our conclusions are supported by comparing execution times between massively parallel implementations of both algorithms, showing that both experience similar decreases in computation time, but that CBP takes significantly longer to form an image.
Date: October 1, 1996
Creator: Knittle, C.D.; Doren, N.E. & Jakowatz, C.V.
Partner: UNT Libraries Government Documents Department

Coherent change detection and interferometric ISAR measurements in the folded compact range

Description: A folded compact range configuration has been developed ant the Sandia National Laboratories` compact range antenna and radar-cross- section measurement facility as a means of performing indoor, environmentally-controlled, far-field simulations of synthetic aperture radar (SAR) measurements of distributed target samples (i.e. gravel, sand, etc.). The folded compact range configuration has previously been used to perform coherent-change-detection (CCD) measurements, which allow disturbances to distributed targets on the order of fractions of a wavelength to be detected. This report describes follow-on CCD measurements of other distributed target samples, and also investigates the sensitivity of the CCD measurement process to changes in the relative spatial location of the SAR sensor between observations of the target. Additionally, this report describes the theoretical and practical aspects of performing interferometric inverse-synthetic-aperture-radar (IFISAR) measurements in the folded compact range environment. IFISAR measurements provide resolution of the relative heights of targets with accuracies on the order of a wavelength. Several examples are given of digital height maps that have been generated from measurements performed at the folded compact range facility.
Date: August 1, 1996
Creator: Sorensen, K.W.
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

LLNL electro-optical mine detection program

Description: Under funding from the Advanced Research Projects Agency (ARPA) and the US Marine Corps (USMC), Lawrence Livermore National Laboratory (LLNL) has directed a program aimed at improving detection capabilities against buried mines and munitions. The program has provided a national test facility for buried mines in arid environments, compiled and distributed an extensive data base of infrared (IR), ground penetrating radar (GPR), and other measurements made at that site, served as a host for other organizations wishing to make measurements, made considerable progress in the use of ground penetrating radar for mine detection, and worked on the difficult problem of sensor fusion as applied to buried mine detection. While the majority of our effort has been concentrated on the buried mine problem, LLNL has worked with the U.S.M.C. on surface mine problems as well, providing data and analysis to support the COBRA (Coastal Battlefield Reconnaissance and Analysis) program. The original aim of the experimental aspect of the program was the utilization of multiband infrared approaches for the detection of buried mines. Later the work was extended to a multisensor investigation, including sensors other than infrared imagers. After an early series of measurements, it was determined that further progress would require a larger test facility in a natural environment, so the Buried Object Test Facility (BOTF) was constructed at the Nevada Test Site. After extensive testing, with sensors spanning the electromagnetic spectrum from the near ultraviolet to radio frequencies, possible paths for improvement were: improved spatial resolution providing better ground texture discrimination; analysis which involves more complicated spatial queueing and filtering; additional IR bands using imaging spectroscopy; the use of additional sensors other than IR and the use of data fusion techniques with multi-sensor data; and utilizing time dependent observables like temperature.
Date: September 30, 1994
Creator: Anderson, C.; Aimonetti, W.; Barth, M.; Buhl, M.; Bull, N.; Carter, M. et al.
Partner: UNT Libraries Government Documents Department

Inverse-synthetic-aperture imaging of trees over a ground plane

Description: Recent data collections with the Sandia VHF-UHF synthetic-aperture radar have yielded surprising results; trees appear brighter in the images than expected! In an effort to understand this phenomenon, various small trees have been measured on the Sandia folded compact range with the inverse-synthetic-aperture imaging system. A compilation of these measurements is contained in this report.
Date: November 1, 1995
Creator: Zittel, D.H.; Brock, B.C.; Littlejohn, J.H. & Patitz, W.E.
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

Joint UK/US Radar Program progress reports for period January 1--31, 1995

Description: Our current objectives are to modify the Hughes x-band radar for airborne implementation, to upgrade it to polarimetry, high-power, and add SLAR mode, and then to deploy in UK/US field experiments as needed. We are on schedule and within budget on bringing the airborne (Hughes A-3) system for future SAR and eventually, SLAR imaging at low grazing angles. Hughes and LLNL continued work on system integration, radar hardware, and associated control hardware and software. The belly radome design modification previously completed is now being procured. The overall radar and testbed remains on schedule for engineering checkout in April 1995, pending the arrival of FY95 funds as expected.
Date: February 15, 1995
Creator: Twogood, R.E.; Brase, J.M.; Robey, H.F.; Mantrom, D.D.; Rino, C.; Chambers, D.H. et al.
Partner: UNT Libraries Government Documents Department

Joint UK/US Radar Program progress reports for period December 1--31, 1994

Description: Topics discussed in this report are current accomplishments in many functions to include: airborne RAR/SAR, radar data processor, ground based SAR signal processing workstation, static airborne radar, multi-aperture space-time array radar, radar field experiments, data analysis and detection theory, management, radar data analysis, modeling and analysis, current meter array, UCSB wave tank, stratified flow facility, Russian Institute of Applied Physics, and budget status.
Date: January 23, 1995
Creator: Twogood, R.E.; Brase, J.M.; Mantrom, D.D.; Rino, C.; Chambers, D.H.; Robey, H.F. et al.
Partner: UNT Libraries Government Documents Department

FESDIF -- Finite Element Scalar Diffraction theory code

Description: This document describes the theory and use of a powerful scalar diffraction theory based computer code for calculation of intensity fields due to diffraction of optical waves by two-dimensional planar apertures and lenses. This code is called FESDIF (Finite Element Scalar Diffraction). It is based upon both Fraunhofer and Kirchhoff scalar diffraction theories. Simplified routines for circular apertures are included. However, the real power of the code comes from its basis in finite element methods. These methods allow the diffracting aperture to be virtually any geometric shape, including the various secondary aperture obstructions present in telescope systems. Aperture functions, with virtually any phase and amplitude variations, are allowed in the aperture openings. Step change aperture functions are accommodated. The incident waves are considered to be monochromatic. Plane waves, spherical waves, or Gaussian laser beams may be incident upon the apertures. Both area and line integral transformations were developed for the finite element based diffraction transformations. There is some loss of aperture function generality in the line integral transformations which are typically many times more computationally efficient than the area integral transformations when applicable to a particular problem.
Date: September 1, 1992
Creator: Kraus, H.G.
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

Processing of polarametric SAR images. Final report

Description: The objective of this work was to develop a systematic method of combining multifrequency polarized SAR images. It is shown that the traditional methods of correlation, hard targets, and template matching fail to produce acceptable results. Hence, a new algorithm was developed and tested. The new approach combines the three traditional methods and an interpolation method. An example is shown that demonstrates the new algorithms performance. The results are summarized suggestions for future research are presented.
Date: September 1, 1995
Creator: Warrick, A.L. & Delaney, P.A.
Partner: UNT Libraries Government Documents Department

On the detection of crevasses in glacial ice with synthetic-aperture radar.

Description: The intent of this study is to provide an analysis of the scattering from a crevasse in Antarctic ice, utilizing a physics-based model for the scattering process. Of primary interest is a crevasse covered with a snow bridge, which makes the crevasse undetectable in visible-light images. It is demonstrated that a crevasse covered with a snow bridge can be visible in synthetic-aperture-radar (SAR) images. The model of the crevasse and snow bridge incorporates a complex dielectric permittivity model for dry snow and ice that takes into account the density profile of the glacier. The surface structure is based on a fractal model that can produce sastrugi-like features found on the surface of Antarctic glaciers. Simulated phase histories, computed with the Shooting and Bouncing Ray (SBR) method, are processed into SAR images. The viability of the SBR method for predicting scattering from a crevasse covered with a snow bridge is demonstrated. Some suggestions for improving the model are given.
Date: February 1, 2010
Creator: Brock, Billy C.
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

A novel polar format algorithm for SAR images utilizing post azimuth transform interpolation.

Description: SAR phase history data represents a polar array in the Fourier space of a scene being imaged. Polar Format processing is about reformatting the collected SAR data to a Cartesian data location array for efficient processing and image formation. In a real-time system, this reformatting or ''re-gridding'' operation is the most processing intensive, consuming the majority of the processing time; it also is a source of error in the final image. Therefore, any effort to reduce processing time while not degrading image quality is valued. What is proposed in this document is a new way of implementing real-time polar-format processing through a variation on the traditional interpolation/2-D Fast Fourier Transform (FFT) algorithm. The proposed change is based upon the frequency scaling property of the Fourier Transform, which allows a post azimuth FFT interpolation. A post azimuth processing interpolation provides overall benefits to image quality and potentially more efficient implementation of the polar format image formation process.
Date: September 1, 2005
Creator: Holzrichter, Michael Warren; Martin, Grant D. & Doerry, Armin Walter
Partner: UNT Libraries Government Documents Department

Autofocus correction of excessive migration in synthetic aperture radar images.

Description: When residual range migration due to either real or apparent motion errors exceeds the range resolution, conventional autofocus algorithms fail. A new migration-correction autofocus algorithm has been developed that estimates the migration and applies phase and frequency corrections to properly focus the image.
Date: September 1, 2004
Creator: Doerry, Armin Walter
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

Antarctica X-band MiniSAR crevasse detection radar : final report.

Description: This document is the final report for the Antarctica Synthetic Aperture Radar (SAR) Project. The project involved the modification of a Sandia National Laboratories MiniSAR system to operate at X-band in order to assess the feasibility of an airborne radar to detect crevasses in Antarctica. This radar successfully detected known crevasses at various geometries. The best results were obtained for synthetic aperture radar resolutions of at most one foot and finer. In addition to the main goal of detecting crevasses, the radar was used to assess conops for a future operational radar. The radar scanned large areas to identify potential safe landing zones. In addition, the radar was used to investigate looking at objects on the surface and below the surface of the ice. This document includes discussion of the hardware development, system capabilities, and results from data collections in Antarctica.
Date: September 1, 2007
Creator: Sander, Grant J. & Bickel, Douglas Lloyd
Partner: UNT Libraries Government Documents Department

Automatic compensation of antenna beam roll-off in SAR images.

Description: The effects of a non-uniform antenna beam are sometimes visible in Synthetic Aperture Radar (SAR) images. This might be due to near-range operation, wide scenes, or inadequate antenna pointing accuracy. The effects can be mitigated in the SAR image by fitting very a simple model to the illumination profile and compensating the pixel brightness accordingly, in an automated fashion. This is accomplished without a detailed antenna pattern calibration, and allows for drift in the antenna beam alignments.
Date: April 1, 2006
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