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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Sea ice motions in the Central Arctic pack ice as inferred from AVHRR imagery

Synoptic observations of ice motion in the Arctic Basin are currently limited to those acquired by drifting buoys and, more recently, radar data from ERS-1. Buoys are not uniformly distributed throughout the Arctic, and SAR coverage is currently limited regionally and temporally due to the data volume, swath width, processing requirements, and power needs of the SAR. Additional ice-motion observations that can map ice responses simultaneously over large portions of the Arctic on daily to weekly time intervals are thus needed to augment the SAR and buoys data and to provide an intermediate-scale measure of ice drift suitable for climatological analyses and ice modeling. Principal objectives of this project were to: (1) demonstrate whether sufficient ice features and ice motion existed within the consolidated ice pack to permit motion tracking using AVHRR imagery; (2) determine the limits imposed on AVHRR mapping by cloud cover; and (3) test the applicability of AVHRR-derived motions in studies of ice-atmosphere interactions. Each of these main objectives was addressed. We conclude that AVHRR data, particularly when blended with other available observations, provide a valuable data set for studying sea ice processes. In a follow-on project, we are now extending this work to cover larger areas and to address science questions in more detail.

Emery, William↗
NASA NTRS1996

On Board Processor Development for NASA's Advanced Radar Technology Program

This paper reports a preliminary study result of an on-board spaceborne SAR processor. It consists of a processing requirement analysis, functional specifications on custom hardware, and consideration on implementation approaches. Finally, a minimum version of this on-board processor designed for performance evaluation and for partial demonstration is illustrated.

SAR radar on-board processing spacecraft mapping i↗
NASA NTRS1986

Off-line processing of ERS-1 synthetic aperture radar data with high precision and high throughput

The first European remote sensing satellite ERS-1 will be launched by the European Space Agency (ESA) in 1989. The expected lifetime is two to three years. The spacecraft sensors will primarily support ocean investigations and to a limited extent also land applications. Prime sensor is the Active Microwave Instrumentation (AMI) operating in C-Band either as Synthetic Aperture Radar (SAR) or as Wave-Scatterometer and simultaneously as Wind-Scatterometer. In Europe there will be two distinct types of processing for ERS-1 SAR data, Fast Delivery Processing and Precision Processing. Fast Delivery Proceessing will be carried out at the ground stations and up to three Fast Delivery products per pass will be delivered to end users via satellite within three hours after data acquisition. Precision Processing will be carried out in delayed time and products will not be generated until several days or weeks after data acquisition. However, a wide range of products will be generated by several Processing and Archiving Facilities (PAF) in a joint effort coordinated by ESA. The German Remote Sensing Data Center (Deutsches Fernerkundungsdatenzentrum DFD) will develop and operate one of these facilities. The related activities include the acquisition, processing and evaluation of such data for scientific, public and commercial users. Based on this experience the German Remote Sensing Data Center is presently performing a Phase-B study regarding the development of a SAR processor for ERS-1. The conceptual design of this processing facility is briefly outlined.

Gredel, J.↗
NASA NTRS1984

Real-time synthetic aperture radar processing

Real-time acousto-optic SAR processors are described and experimentally demonstrated. SAR imaging is performed in one of the architectures by applying the signal to an acousto-optic device and correlating it with chirp signals recorded on an optical transparency by time integration on a CCD detector. In a different implementation, the imaging is preformed by interfering the light beams diffracted from two separate acousto-optic devices, one modulated the radar signal and the second by the reference chirp waveform.

Psaltis, D.↗
NASA NTRS1992

Surface processes on Venus

Magellan synthetic aperture radar (SAR) and altimetry data were analyzed to determine the nature and extent of surface modification for venusian plains in the Sedna Planitia, Alpha Regio, and western Ovda Regio areas. Specific cross sections derived from the SAR data were also compared to similar data for dry terrestrial basaltic lava flows (Lunar Crater and Cima volcanic fields) and playas (Lunar and Lavic Lakes) for which microtopographic profiles (i.e., quantitative roughness information) were available.

Arvidson, R. E.↗
NASA NTRS1980

An unusual SAR arc observed during ring current development, 4 August 1972

An unusual SAR arc observed during the growth phase of the ring current is described. Proton precipitation was observed, with electron temperature enhancements throughout the region, and an F-region trough present at the equatorward boundary; a high flux of low energy at the SAR arc location and a 'slot' in the ambient electron density are characteristic of this event. Comparisons are made with S3-A spacecraft observations made in the equatorial region at the same time and with Isis-II observations of a more normal SAR arc; the kinetic Alfven process described by Hasegawa and Mima (1978) appears to account for the acceleration of these low energy electrons, although an auroral-type acceleration process cannot be excluded.

Shepherd, G. G.↗
NASA NTRS1981

A derivation of the statistical characteristics of SAR imagery data

Basic statistical properties of the speckle effect and the associated spatial correlation of SAR image data are discussed. Statistics of SAR sensed measurement and their relationships to the surface mean power reflectivity are derived. The Rayleigh speckle model is reviewed. Applications of the derived statistics to SAR radiometric measures and image processing are considered.

Wu, C.↗
NASA NTRS1980

Analysis of urban area land cover using SEASAT Synthetic Aperture Radar data

Digitally processed SEASAT synthetic aperture raar (SAR) imagery of the Denver, Colorado urban area was examined to explore the potential of SAR data for mapping urban land cover and the compatability of SAR derived land cover classes with the United States Geological Survey classification system. The imagery is examined at three different scales to determine the effect of image enlargement on accuracy and level of detail extractable. At each scale the value of employing a simplistic preprocessing smoothing algorithm to improve image interpretation is addressed. A visual interpretation approach and an automated machine/visual approach are employed to evaluate the feasibility of producing a semiautomated land cover classification from SAR data. Confusion matrices of omission and commission errors are employed to define classification accuracies for each interpretation approach and image scale.

Henderson, F. M.↗
NASA NTRS1985

Contour-Mapping Synthetic-Aperture Radar

Airborne two-antenna synthetic-aperture-radar (SAR) interferometric system provides data processed to yield terrain elevation as well as reflectedintensity information. Relative altitudes of terrain points measured to within error of approximately 25 m.

Goldstein, R. M.↗
NASA NTRS1989

Effects of the ephemeris error on effective pointing for a spaceborne SAR

Both Magellan SAR data acquisition and image processing require the knowledge of both the ephemeris (spacecraft position and velocity) and the radar pointing direction. Error in the knowledge of the radar pointing direction results in a loss of SNR in the image product. An error in the ephemeris data has a similar effect. To facilitate SNR performance analysis, an effective pointing error is defined to characterize the effect of the ephemeris error. A systematic approach to relate the ephemeris error to the effective pointing errors is described. Result of this analysis has led to a formal accuracy requirement levied on the Magellan navigation system.

Jin, Michael Y.↗
NASA NTRS1994

Analysis of coseismic surface displacement gradients using radar interferometry: New insights into the Landers earthquake

The map of the coseismic displacement field generated by interferometric processing of synthetic aperture radar (SAR) images taken before and after the June 28, 1992, Landers earthquake sequence brings new insights into the nature of deformation caused by these earthquakes. We use the interferometric map generated by Massonnet et al. (1993) to analyze the surface displacement field in the vicinity of the fault trace. Complexities in the fringe pattern near the fault reflect short-wavelength variations of the surface rupture and slip distribution, and attest to large displacement gradients. Along two sections of the fault, characteristic fringe patterns can be recognized, contrasting in density and direction with patterns observed away from the rupture. In order to understand the observed fringe patterns, we compute synthetic interferograms in three simple cases: (1) rigid-body rotations about a vertical axis, (2) about a horizontal axis (tilt), and (3) distributed, simple shear. The orientation and spatial separation of interferometric fringes predicted by these models help constrain near-field deformation and rupture parameters. Where the Kickapoo fault connects with the Homestead Valley fault, the interferogram shows a clear pattern of parallel N20 deg W fringes separated by about 160 m. This pattern and vertical offsets measured along the Kickapoo fault suggest that the block between this fault and the Johnson Valley fault may have been tilted, down to the west. A 5-km block lifted by 1 m on one side would be tilted by an angle of 0.01 deg (190 microrad), producing fringes separated by about 160 m, parallel to the tilt axis. Such a tilt, parallel to a N20 deg W direction, would account for the gradual, northward increase of the vertical slip component observed along the Kickapoo fault. This tilt may also explain the 1 m of reverse slip observed along the 'slip gap' section of the Homestead Valley break. Between the southern end of the Johnson Valley fault and the Eureka Peak fault, where no surface rupture has been mapped, the dense pattern of fringes implies distributed shear, probably resulting from fault slip at depth. The density and direction of the fringes in the gap are consistent with a right-lateral slip of 1.2-3.8 m on a blind fault locked above the depth of 1.5-2 km. Such observations of small wavelength features in the SAR interferogram bring new insights into the near-field displacement gradient and thus on response of the uppermost crust to seismic rupture.

Peltzer, Gilles↗
NASA NTRS1995

Optimal Estimation Of Range And Doppler Centroid In ScanSAR

Algorithm processes synthetic-aperture-radar (SAR) returns into optimal estimates of ranges, pointing angles, and Doppler centroids. Derives radar-beam-pointing angles partly from SAR data. Exploits information available in overlapping regions between adjacent image bursts or, equivalently, between adjacent radar beams corresponding to adjacent image bursts. Range or Doppler centroid obtained from estimate of range or Doppler value at which intensity in one image burst equals that in adjacent burst.

Jin, Michael Y.↗
NASA NTRS1993

An Efficient Image Recovery Algorithm for Diffraction Tomography Systems

A diffraction tomography system has potential application in ultrasonic medical imaging area. It is capable of achieving imagery with the ultimate resolution of one quarter the wavelength by collecting ultrasonic backscattering data from a circular array of sensors and reconstructing the object reflectivity using a digital image recovery algorithm performed by a computer. One advantage of such a system is that is allows a relatively lower frequency wave to penetrate more deeply into the object and still achieve imagery with a reasonable resolution. An efficient image recovery algorithm for the diffraction tomography system was originally developed for processing a wide beam spaceborne SAR data...

Jin, Michael Y.↗
NASA NTRS2024

COLUTA: Custom 8-Channel 15-bit 40-MSPS ADC for the ATLAS Liquid Argon Calorimeter Readout

The stringent radiation-tolerance, quantization requirements, and the need for seamless integration of the on-detector readout electronics chain require the design of a full-custom analog-to-digital converter (ADC) for the 182,468 channels in the ATLAS Liquid Argon (LAr) calorimeter at the Large Hadron Collider (LHC) at CERN, as part of the High-Luminosity LHC (HL-LHC) upgrade. Each of the 8 channels in the prototype 65 nm CMOS ADC with 15-bit resolution and >68 dB signal-to-noise-and-distortion ratio (SNDR), or equivalently >11 effective number of bits (ENOB), consists of a Multiplying-DAC (MDAC) and a successive-approximation (SAR) ADC. A digital data processing unit (DDPU) calibrates and serially transmits the quantized data. Initial lab characterization of 18 chips shows a minimum SNDR of 69.5 dB at full-scale at about 5 MHz and a maximum power consumption of 1.17 W; differential non-linearity (DNL) measurements show no missing codes. Additional validation of the ADC is ongoing before approximately 70k chips can be mass-produced for the upgrade.

Rui Xu↗
NASA NTRS1993

Characteristics of arachnoids from Magellan data

Current high resolution Magellan data enables more detailed geological study of arachnoids, first identified by Barsukov et al. as features characterized by a combination of radar-bright, concentric rings and radiating lineations, named 'arachnoids' on the basis of their spider and web-like appearance. Identification of arachnoids in Magellan data has been based on SAR images, in keeping with the original definition. However, there is some overlap by other workers in identification of arachnoids, corona (predominantly bright rings), and novae (predominantly radiating lineations), as all of these features share some common characteristics. Features used in this survey were chosen based on their classification as arachnoids in Head et al.'s catalog and on SAR characteristics matching Barsukov et al.'s original definition. The 259 arachnoids have been currently identified on Venus, all of which were considered in this study. Fifteen arachnoids from different regions, chosen for their 'type' characteristics and lack of deformation by other regional processes, were studied in depth, using SAR and altimetric data to map and profile these arachnoids in an attempt to better determine their geologic and altimetric characteristics and possible formation sequences.

Dawson, C. B.↗
NASA NTRS1996

Air Traffic Complexity Measurement Environment (ACME): Software User's Guide

A user's guide for the Air Traffic Complexity Measurement Environment (ACME) software is presented. The ACME consists of two major components, a complexity analysis tool and user interface. The Complexity Analysis Tool (CAT) analyzes complexity off-line, producing data files which may be examined interactively via the Complexity Data Analysis Tool (CDAT). The Complexity Analysis Tool is composed of three independently executing processes that communicate via PVM (Parallel Virtual Machine) and Unix sockets. The Runtime Data Management and Control process (RUNDMC) extracts flight plan and track information from a SAR input file, and sends the information to GARP (Generate Aircraft Routes Process) and CAT (Complexity Analysis Task). GARP in turn generates aircraft trajectories, which are utilized by CAT to calculate sector complexity. CAT writes flight plan, track and complexity data to an output file, which can be examined interactively. The Complexity Data Analysis Tool (CDAT) provides an interactive graphic environment for examining the complexity data produced by the Complexity Analysis Tool (CAT). CDAT can also play back track data extracted from System Analysis Recording (SAR) tapes. The CDAT user interface consists of a primary window, a controls window, and miscellaneous pop-ups. Aircraft track and position data is displayed in the main viewing area of the primary window. The controls window contains miscellaneous control and display items. Complexity data is displayed in pop-up windows. CDAT plays back sector complexity and aircraft track and position data as a function of time. Controls are provided to start and stop playback, adjust the playback rate, and reposition the display to a specified time.

Source record↗
NASA NTRS1997

Advanced Algorithms and High-Performance Testbed for Large-Scale Site Characterization and Subsurface Target Detecting Using Airborne Ground Penetrating SAR

A team of US Army Corps of Engineers, Omaha District and Engineering and Support Center, Huntsville, let Propulsion Laboratory (JPL), Stanford Research Institute (SRI), and Montgomery Watson is currently in the process of planning and conducting the largest ever survey at the Former Buckley Field (60,000 acres), in Colorado, by using SRI airborne, ground penetrating, Synthetic Aperture Radar (SAR). The purpose of this survey is the detection of surface and subsurface Unexploded Ordnance (UXO) and in a broader sense the site characterization for identification of contaminated as well as clear areas. In preparation for such a large-scale survey, JPL has been developing advanced algorithms and a high-performance restbed for processing of massive amount of expected SAR data from this site. Two key requirements of this project are the accuracy (in terms of UXO detection) and speed of SAR data processing. The first key feature of this testbed is a large degree of automation and a minimum degree of the need for human perception in the processing to achieve an acceptable processing rate of several hundred acres per day. For accurate UXO detection, novel algorithms have been developed and implemented. These algorithms analyze dual polarized (HH and VV) SAR data. They are based on the correlation of HH and VV SAR data and involve a rather large set of parameters for accurate detection of UXO. For each specific site, this set of parameters can be optimized by using ground truth data (i.e., known surface and subsurface UXOs). In this paper, we discuss these algorithms and their successful application for detection of surface and subsurface anti-tank mines by using a data set from Yuma proving Ground, A7, acquired by SRI SAR.

Fijany, Amir↗