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At least 991 records · Page 55

Machine vision and the OMV

The orbital Maneuvering Vehicle (OMV) is intended to close with orbiting targets for relocation or servicing. It will be controlled via video signals and thruster activation based upon Earth or space station directives. A human operator is squarely in the middle of the control loop for close work. Without directly addressing future, more autonomous versions of a remote servicer, several techniques that will doubtless be important in a future increase of autonomy also have some direct application to the current situation, particularly in the area of image enhancement and predictive analysis. Several techniques are presentet, and some few have been implemented, which support a machine vision capability proposed to be adequate for detection, recognition, and tracking. Once feasibly implemented, they must then be further modified to operate together in real time. This may be achieved by two courses, the use of an array processor and some initial steps toward data reduction. The methodology or adapting to a vector architecture is discussed in preliminary form, and a highly tentative rationale for data reduction at the front end is also discussed. As a by-product, a working implementation of the most advanced graphic display technique, ray-casting, is described.

Mcanulty, M. A.↗

The Imaging Spectrometric Observatory

Design and performance features of the Imaging Spectrometric Observatory (ISO) first flown on Spacelab 1 for atmospheric, earth surface and stellar monitoring are outlined. The ISO has five grating spectrometers fitted with CCD arrays for simultaneously gathering spectral and spatial data. The instrument covered the 300-12,700 A range on the Spacelab 1 flight, when it was mounted on a pallet and used for atmospheric scans at high solar zenith angles. A future mission is planned which will include limb-viewing of OH, NO, ClO and NO2 radicals in the middle atmosphere to complement the data collected in the Upper Atmosphere Research Satellite program. Technical details are presented of the instrument components and ground- and balloon-borne test results.

Torr, D. G.↗

8.3 and 12.4 micron imaging of the Galactic Center source complex with the Goddard infrared array camera

A 30 x 30 arcsec field at the Galactic Center (1.5 x 1.5 parsec) was mapped at 8.3 microns and 12.41 microns with high spatial resolution and accurate relative astrometry, using the 16 x 16 Si:Bi accumulation mode charge injection device Goddard infrared array camera. The design and performance of the array camera detector electronics system and image data processing techniques are discussed. Color temperature and dust opacity distributions derived from the spatially accurate images indicate that the compact infrared sources and the large scale ridge structure are bounded by warmer, more diffuse material. None of the objects appear to be heated appreciably by internal luminosity sources. These results are consistent with the model proposing that the complex is heated externally by a strong luminosity source at the Galactic Center, which dominates the energetics of the inner few parsecs of the galaxy.

Gezari, D. Y.↗

Recent progress in the Urbana MST radar

The Urbana radar, which operates at 40.92 MHz with a peak power of about 1.2 MW into a 100 x 120 m phased array antenna was improved. An accelerated data-acquisition system, a beam-steering system, and a transmit/receive switch were installed. With these changes, the radar is in regular operations for two hours every day around local noon gathering stratospheric and mesospheric data. Special campaigns are mounted in addition under severe weather conditions.

Bowhill, S. A.↗

Dust environment of Comet Halley

Advances in the understanding of comet Halley's dust environment are highlighted. Spacecraft results on the dust composition, the detection of subfemtogram grains, and the particle-mass distribution; jets and the dust-emission pattern; the existence of discrete sources on the nucleus surface and the determination of their locations from day-to-day motions of coma features; CN jets; large-scale phenomena, including an antitail, streamers, and a sunward spike; infrared observations, such as the 3.4 microns emission feature, applications of array detectors, and rare far-infrared data; the chemical modification of low-temperature ices by UV and cosmic-ray irradiation processes, their laboratory simulations, and applications to the evolution of comets; the interstellar-connection models of comet origin; and the formation of a mantle made of refractory organic material on the nucleus surface.

Sekanina, Z.↗

Low frequency VLBI

There are many important astrophysical questions which could be answered with observations at frequencies of a few MHz and angular resolution of an arcmin or better. For example, strong interstellar and interplanetary scattering of EM radiation could be studied along many lines of sight, and the sizes and shapes of scattering disks could be directly measured as a function of time and frequency. Such data can be obtained with an interferometer array composed of several small satellites in earth orbit. The individual satellites for an LF array could be very small and inexpensive.

Jones, Dayton L.↗

Evaluation of the airborne visible-infrared imaging spectrometer for mapping subtle lithological variation

The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), flown aboard the NASA ER-2 aircraft in 1987 and 1989, used four linear arrays and four individual spectrometers to collect data simultaneously from the 224 bands in a scanned 614 pixel-wide swath perpendicular to the aircraft direction. The research had two goals. One was to evaluate the AVIRIS data. The other was to look at the subtle lithological variation at the two test sites to develop a better understanding of the regional geology and surficial processes. The geometric characteristics of the data, adequacy of the spatial resolution, and adequacy of the spectral sampling interval are evaluated. Geologic differences at the test sites were mapped. They included lithological variation caused by primary sedimentary layering, facies variation, and weathering; and subtle mineralogical differences caused by hydrothermal alterations of igneous and sedimentary rocks. The investigation used laboratory, field, and aircraft spectral measurements; known properties of geological materials; digital image processing and spectrum processing techniques; and field geologic data to evaluate the selected characteristics of the AVIRIS data.

Kruse, Fred A.↗

Real time thermal imaging for analysis and control of crystal growth by the Czochralski technique

A real time thermal imaging system with temperature resolution better than +/- 0.5 C and spatial resolution of better than 0.5 mm has been developed. It has been applied to the analysis of melt surface thermal field distributions in both Czochralski and liquid encapsulated Czochralski growth configurations. The sensor can provide single/multiple point thermal information; a multi-pixel averaging algorithm has been developed which permits localized, low noise sensing and display of optical intensity variations at any location in the hot zone as a function of time. Temperature distributions are measured by extraction of data along a user selectable linear pixel array and are simultaneously displayed, as a graphic overlay, on the thermal image.

Wargo, M. J.↗

The Effects of Vortex Ingestion on the Flow in a Diffusing S-duct

An experimental study of the effects of an ingested vortex on the flowfield of a diffusing S-duct is reported. The vortex is generated through the use of a stationary pinwheel device mounted upstream of the diffusing S-duct. Three test conditions vary the location of the vortex in the duct inlet crossplane. For each condition of ingested vortex, a baseline S-duct and an S-duct with an array of vortex generators is examined. The data taken consist of duct inlet and exit crossplane surveys of velocity and total pressure. Duct surface flow visualization and static pressure are also recorded. The data acquired in these tests are compared to identical S-duct data taken in the absence of the ingested vortex. The ingested vortex is observed to have a strong influence on the flowfield inside (and exiting) the S-duct, but only when the vortex impinges at the inlet crossplane location coincident with the crossplane location of downstream flow separation within the duct. When the ingested vortex impinges at this location it reduces the extent of flowfield separation inside the baseline duct and promotes stronger crossflow in the exit plane of both the baseline duct and the duct with installed vortex generators. This enhanced crossflow also strengthens the vortices shed from the vortex generators. The other impingement locations of the ingested vortex are found to produce little effect on the flowfield of the duct with or without vortex generators.

Wendt, B. J.↗

Radio properties of narrow-lined Seyfert 1 galaxies

We have observed seven narrow-linedd Seyfert 1 (NLS1) galaxies and one high-ionization Seyfert 2 galaxy with the Very Large Array (VLA). Combining these observations with published data, we summarize the radio properties of the NLS1 galaxies for which spectropolarimetry was reported by Goodrich. Fifteen of these 17 objects now have published radio observations of high sensitivity, and only nine of those have been detected. For a Hubble parameter of 75 km/s/Mpc, the 6 cm radio powers range from 10(exp 20) to 10(exp 23) W/Hz, within the range previously found for other types of Seyfert galaxy. The median radio size of the nine VLA-detected galaxies is no larger than 300 pc, similar to the median size found by Ulvestad & Wilson for a distance-limited sample of Seyfert galaxies. Of the six NLS1 galaxies known to have significant intrinsic optical polarization, three have measurable radio axes. Two of those three galaxies have radio major axes close to 90 deg from their polarization position angles, while the third has an inner radio axis that may be nearly parallel to the polarization position angle. The former relationship is expected for a Seyfert 1 in a unified model of Seyfert galaxies, assuming no intrinsic continuum polarization.

Ulvestad, James S.↗

The chemical and radiative effects of the Mount Pinatubo eruption

To clarify the mechanisms leading to effects on stratospheric ozone, time-dependent stratospheric aerosol and gas experiment II (SAGE II) and cryogenic limb array elaton spectrometer (CLAES) aerosol optical extinction data and SAGE II surface area density are used as parameters in a two-dimensional (2-D) zonally averaged chemical radiative transport model. The model was integrated with time from before the eruption through December 1993. The modeled impact on global ozone results from increased rates of heterogeneous reactions on sulfate aerosols and from the increased radiative heating and scattering caused by these aerosols. When the aerosol heating is allowed to modify the temperature distribution, the maximum change calculated in equatorial column ozone is -1.6%. The calculated equatorial temperature change and peak local ozone change in October 1991 are +6K and -4%, respectively. When aerosol heating perturbs the circulation in the model, the maximum change in equatorial column ozone is -6%. Increased heterogeneous processing on sulfate aerosols is calculated to have changed equatorial column ozone in late 1991 by -1.5%. Global column ozone in the model in 1992 and 1993 changed by -2.8% and -2.4%, respectively. The relationship of ozone-controlling processes in the lower stratosphere is altered as well; HO(x) becomes the most important catalytic cycle, followed by ClO(x) and NO(x). This is driven by significant changes in trace gas concentrations. In October 1991, lower stratospheric, equatorial NO(x) decreased by 40%, ClO(x) increased by 60%, and HO(x) increased by 25%. When the effect of heterogeneous chemical processing on sulfate aerosols is combined with aerosol heating, modifying either circulation or temperature, dramatically different ozone fingerprints with time and latitude are predicted. Model-derived changes in the equatorial region in column ozone best represented the observed data when perturbed circulation was combined with heterogeneous chemical effects. However, at high latitudes, the increased ozone production from the strengthening of the mean circulation tends to cancel the heterogeneous reduction of ozone. This is not in good agreement with observed data, especially in 1992 and 1993. When the circulation is held fixed and the temperature allowed to change, and heterogeneous chemical effects are included, the equatorial ozone decrease predicted was too small for 1991. However, the mid- to high-latitude decrease in 1992 and 1993 is in better agreement with observed data.

Kinneson, Douglas E.↗

Optimum combining of residual carrier array signals in correlated noises

An array feed combining system for the recovery of signal-to-noise ratio (SNR) loss due to antenna reflector deformation has been implemented and is currently being evaluated on the Jet Propulsion Laboratory 34-m DSS-13 antenna. The current signal-combining system operates under the assumption that the white Gaussian noise processes in the received signals from different array elements are mutually uncorrelated. However, experimental data at DSS 13 indicate that these noise processes are indeed mutually correlated. The objective of this work is to develop a signal-combining system optimized to account for the mutual correlations between these noise processes. The set of optimum combining weight coefficients that maximizes the combined signal SNR in the correlated noises environment is determined. These optimum weights depend on unknown signal and noise covariance parameters. A maximum-likelihood approach is developed to estimate these unknown parameters to obtain estimates of the optimum weight coefficients based on residual carrier signal samples. The actual combined signal SNR using the estimated weight coefficients is derived and shown to converge to the maximum achievable SNR as the number of signal samples increases. These results are also verified by simulation. A numerical example shows a significant improvement in SNR performance can be obtained, especially when the amount of correlation increases.

Liang, R.↗

Estimation of Forest Canopy Leaf Area Index Using Directional ASAS Measurements

Coniferous forest canopy reflectance was derived from radiance data collected the Advanced Solid-State Array Spectroradiometer (ASAS). Red and Near-InfraRed (NIR) responses were examined as a function of view zenith angle (theta(sub v)), solar zenith angle (theta(sub s)), and site characteristics. Relationships were formulated between the Normalized Difference Vegetation Index (NDVI) and canopy Leaf Area Index (LAI). It is suggested that the offnadir NDVI is a more stable estimator of LAI than is the nadir-view NDVI.

Johnson, Lee F.↗

Optimum Combining of Residual Carrier Array Signals in Correlated Noises

An array feed combining system for the recovery of signal-to-noise ratio (SNR) loss due to antenna reflector deformation has been implemented and is currently being evaluated on the Jet Propulsion Laboratory 34-m DSS-13 antenna. The current signal-combining system operates under the assumption that the white Gaussian noise processes in the received signals from different array elements are mutually uncorrelated. However, experimental data at DSS 13 indicate that these noise processes are indeed mutually correlated. The objective of this work is to develop a signal-combining system optimized to account for the mutual correlations between these noise processes. The set of optimum combining weight coefficients that maximizes the combined signal SNR in the correlated noises environment is determined. These optimum weights depend on unknown signal and noise covariance parameters. A maximum-likelihood approach is developed to estimate these unknown parameters to obtain estimates of the optimum weight coefficients based on residual carrier signal samples. The actual combined signal SNR using the estimated weight coefficients is derived and shown to converge to the maximum achievable SNR as the number of signal samples increases. These results are also verified by simulation. A numerical example shows a significant improvement in SNR performance can be obtained, especially when the amount of correlation increases.

Tan, H. H.↗

Database Reorganization in Parallel Disk Arrays with I/O Service Stealing

We present a model for data reorganization in parallel disk systems that is geared towards load balancing in an environment with periodic access patterns. Data reorganization is performed by disk cooling, i.e. migrating files or extents from the hottest disks to the coldest ones. We develop an approximate queueing model for determining the effective arrival rates of cooling requests and discuss its use in assessing the costs versus benefits of cooling.

Zabback, Peter↗

A Coordinated RXTE/ASCA Study of Absorption Dips in Circinus X-1 at Phase Zero

This proposal was for an Rossi X Ray Timing Explorer (RXTE) study of Circinus X-1 with the ASCA satellite for the purpose of studying the iron emission feature during intensity dips. These dips had been discovered previously with ASCA and they appeared to vary in equivalent width and in the energy of the iron K edge. Proper analyses requires good continuum measurements which Rossi X Ray Timing Explorer/Proportional Counter Array (RXTE/PCA) could provide. Also, the PCA data would show any temporal evolution correlated with spectral evolution. RXTE provided 90 ks of data during March 3-5, 1998 which included phase zero which is where the dips usually take place. The ASCA observations were taken by Dr. Neil Brandt of Penn State University. Unfortunately, the source intensity showed far less dipping activity than is typical near phase zero. The light curve exhibited only very narrow sporadic dips rather than some long deep dips necessary for sufficient statistics in the ASCA and RXTE instruments for spectral studies. This prevented us from carrying out the primary goal of the proposal.

Bradt, Hale↗

GEOS Instrument of Opportunity (IoO)

NOAA's three-axis stabilized series of GOES satellites have a place reserved on the Earth-facing side for an Instrument of Opportunity (IoO). The IoO slot is a location for new technologies that provide space-time-spectral resolution of the environment not possible with the preconceived Imager and Sounder. For example, candidate IoO's have usually proposed to use large-format staring arrays of detectors. The size, weight, power, data rate, and interface allocations for the IoO are modest in comparison to the Imager and Sounder, but the resources are large enough to allow for the collection of useful real time data. Because, the geosynchronous location is ideal for monitoring rapidly changing unpredictable events, IoO's have been suggested to detect lightning, volcanism, ozone and sulfur dioxide, ocean color, vegetation, special weather events, and even broadcast color TV. To become an IoO on GOES, the proposed instrument must: 1) have potential benefit to NOAA, 2) fit within the allocation constraints, 3) be independently funded, including pre-launch test equipment and the spacecraft accommodation costs, 4) be delivered two years before launch for integration and testing, and 5) not interfere with the existing launch schedule or the operational instruments.

Chesters, Dennis↗

Thermal Analysis and Correlation of the Mars Odyssey Spacecraft's Solar Array During Aerobraking Operations

The Mars Odyssey spacecraft made use of multipass aerobraking to gradually reduce its orbit period from a highly elliptical insertion orbit to its final science orbit. Aerobraking operations provided an opportunity to apply advanced thermal analysis techniques to predict the temperature of the spacecraft's solar array for each drag pass. Odyssey telemetry data was used to correlate the thermal model. The thermal analysis was tightly coupled to the flight mechanics, aerodynamics, and atmospheric modeling efforts being performed during operations. Specifically, the thermal analysis predictions required a calculation of the spacecraft's velocity relative to the atmosphere, a prediction of the atmospheric density, and a prediction of the heat transfer coefficients due to aerodynamic heating. Temperature correlations were performed by comparing predicted temperatures of the thermocouples to the actual thermocouple readings from the spacecraft. Time histories of the spacecraft relative velocity, atmospheric density, and heat transfer coefficients, calculated using flight accelerometer and quaternion data, were used to calculate the aerodynamic heating. During aerobraking operations, the correlations were used to continually update the thermal model, thus increasing confidence in the predictions. This paper describes the thermal analysis that was performed and presents the correlations to the flight data.

Dec, John A.↗