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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Simulated life cycles of persistent anticyclonic anomalies over the North Pacific: Role of synoptic-scale eddies

This study examines the role of synoptic-scale eddies during the development of persistent anticyclonic height anomalies over the central North Pacific in a general circulation model under perpetual January conditions. The General Circulation Model (GCM) replicates the basic characteristics of the evolution of the anomaly patterns found in observations. The life cycle is characterized by the rapid establishment of the major anomaly center and considerably longer maintenance and decay phases, which include the development of downstream anomaly centers. The simulation also shows a realistic evolution of synoptic-scale activity beginning with enhanced activity off the east coast of Asia prior to onset, followed by a northward shift of the Pacific storm track, which lasts throughout the maintenance phase. The initial enhancement of synoptic-scale eddy activity is associated with a large-scale cyclonic anomaly that developes over Siberia several days prior to the onset of the main anticyclonic anomaly over the central North Pacific. The observations, however, show considerable interdecadel variability in the details of the composite onset behavior; it is unclear whether this variability is real or whether it reflects differences in the data assimilation systems. The role of the time mean flow and synoptic-scale eddies in the development of the persistent Pacific anomalies is studied within the context of a kinetic energy budget in which the flow is decomposed into the time-mean, low-frequency (timescales longer than 10 days), and synoptic (timescales less than 6 days) components. The budget, which is carried out for the simulation at 500 mb, shows that the initial growth of the persistent anticyclonic anomalies is associated with barotropic conversions of energy, with approximately equal contributions coming from the mean flow and the synoptic-scale eddies. After onset the barotropic conversion from the mean flow dominates, whereas the decay phase is associated with baroclinic processes within the low-frequency flow.

Higgins, R. W.↗
NASA NTRS1995

Software to model AXAF-I image quality

A modular user-friendly computer program for the modeling of grazing-incidence type x-ray optical systems has been developed. This comprehensive computer software GRAZTRACE covers the manipulation of input data, ray tracing with reflectivity and surface deformation effects, convolution with x-ray source shape, and x-ray scattering. The program also includes the capabilities for image analysis, detector scan modeling, and graphical presentation of the results. A number of utilities have been developed to interface the predicted Advanced X-ray Astrophysics Facility-Imaging (AXAF-I) mirror structural and thermal distortions with the ray-trace. This software is written in FORTRAN 77 and runs on a SUN/SPARC station. An interactive command mode version and a batch mode version of the software have been developed.

Ahmad, Anees↗
NASA NTRS1996

Software For Generation Of ASTER Data Products

Software functioning in EOS-DIS computing environment developed to generate data products from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Processes high-resolution image data from visible and near infrared (VNIR), short-wavelength infrared (SWIR), and thermal infrared (TIR) radiometric readings to generate data on radiative and thermal properties of atmosphere and surface of Earth.

Murray, Alexander T.↗
NASA NTRS1997

The Orbits of Meteorites from Natural Thermoluminescence

The natural thermoluminescence (TL) of meteorites reflects their irradiation and thermal histories. Virtually all ordinary chondrites have been irradiated long enough to reach saturation natural TL levels, and thus natural TL levels in these meteorites are determined largely by thermal history. The primary heat source for most meteorites is the Sun, and thus natural TL levels are determined primarily by the closest approach to the Sun, i.e., perihelion. By converting natural TL levels to perihelia, using an assumed albedo typical of meteoroid bodies, it is found that most ordinary chondrites had perihelia of 0.85 to 1.0 AU prior to reaching Earth. This range is similar to that calculated from meteor and fireball observations. All common classes of ordinary chondrites exhibit similar perihelia distributions; however, H and LL chondrites that fell in the local morning differ in their natural TL distribution from those that fell in the local afternoon or evening. This is consistent with earlier suggestions that time of fall reflects orbital distribution. The data also suggest that the orbits of some of the H chondrites cluster and may have come from a debris 'stream' of meteoroids. If meteorites can exist in "orbital groups," significant changes in the types and number of meteorites reaching Earth could occur on the less than 10(exp 5)-year time scale.

Benoit, P. H.↗
NASA NTRS2000

Experimental Results of the Impact of an Ion Thruster Plasma on Microwave Propagation

Electric thrusters are being considered for a variety of space missions because of the significant propellant savings that result from the use of high performance, electric propulsion technologies, Propellant mass savings reduces spacecraft launch requirements and increases mission lifetime and payload. The impact of electric thruster plasma plumes on microwave signal propagation however is an important spacecraft integration concern. Arcjets were the first electric thrusters to be considered for operational missions. Ling, et al., studied the effect of arcjet plumes on propagation. Arcjets produce a lightly ionized plume and Ling's analysis predicted that the plume would have a negligible effect on communication. Plumes from the higher performance ion thrusters being developed exhibit higher ionization levels, plasma temperatures and particle velo@ities than arcjets. Therefore, there was a need to assess the impact due to these plumes. To address this need, the authors designed and performed a series of experiments to examine propagation effects of plumes. The challenge with these experiments was that they had to be performed in the operational environment of the thruster. Therefore, the experiments were conducted inside a metal chamber which could be depressurized to simulate a near vacuum condition of space. The metal chamber presents a potential large source of error to the propagation measurements due to the corruption of the desired data by multiple wall reflections within the chamber. This chamber effect was minimized by employing a pulsed-continuous wave transmitter and receiver system. This system, based on an HP8510 Network Analyzer, uses external hardware time gating to eliminate the clutter of the spurious reflections. Additionally, high gain antennas were used in the measurements to ensure that minimal amounts of energy ",ere transmitted/received in undesirable directions. The measurements took place in Vacuum Facility 5 of the Electric Propulsion Laboratory at the NASA Glenn Research Center. This facility utilizes a cylindrical, stainless steel, vacuum chamber, which is 18.3 m long and 4.6 m in diameter. For the tests being described here a 30 cm diameter, xenon ion thruster was used. The thruster provided between 500 W and 2.3 kW of operating power. The thruster was mounted on a stand along the axis of the chamber near one of its ends.

Zaman, Afroz J.↗
NASA NTRS2000

Experimental Results of the Impact of an Ion Thruster Plasma on Microwave Propagation

Electric thrusters are being considered for a variety of space missions because of the significant propellant savings that result from the use of high performance, electric propulsion technologies. Propellant mass savings reduces spacecraft launch requirements and increases mission lifetime and payload. The impact of electric thruster plasma plumes on microwave signal propagation however is an important spacecraft integration concern. Arcjets were the first electric thrusters to be considered for operational missions. Ling, et al. studied the effect of arcjet plumes on propagation. Arcjets produce a lightly ionized plume and Ling's analysis predicted that the plume would have a negligible effect on communication. Plumes from the higher performance ion thrusters being developed exhibit higher ionization levels, plasma temperatures and particle velocities than arcjets. Therefore, there was a need to assess the impact due to these plumes. To address this need, the authors designed and performed a series of experiments to examine propagation effects of plumes. The challenge with these experiments was that they had to be performed in the operational environment of the thruster. Therefore, the experiments were conducted inside a metal chamber which could be depressurized to simulate a near vacuum condition of space. The metal chamber presents a potential large source of error to the propagation measurements due to the corruption of the desired data by multiple wall reflections within the chamber. This chamber effect was minimized by employing a pulsed-continuous wave transmitter and receiver system. This system based on an HP8510 Network Analyzer, uses external hardware time gating to eliminate the clutter of the spurious reflections. Additionally, high gain antennas were used in the measurements to ensure that minimal amounts of energy were transmitted/received in undesirable directions. The measurements took place in Vacuum Facility 5 of the Electric Propulsion Laboratory at the NASA Glenn Research Center. This facility utilizes a cylindrical, stainless steel, vacuum chamber, which is 18.3 m long and 4.6 m in diameter. For the tests being described here a 30 cm diameter, xenon ion thruster was used. The thruster provided between 500 W and 2.3 kW of operating power. The thruster was mounted on a stand along the axis of the chamber near one of its ends and could be moved axially.

Zaman, Afroz J.↗
NASA NTRS1998

Issues in Absolute Spectral Radiometric Calibration: Intercomparison of Eight Sources

The application of atmospheric models to AVIRIS and other spectral imaging data to derive surface reflectance requires that the sensor output be calibrated to absolute radiance. Uncertainties in absolute calibration are to be expected, and claims of 92% accuracy have been published. Measurements of accurate surface albedos and cloud absorption to be used in radiative balance calculations depend critically on knowing the absolute spectral-radiometric response of the sensor. The Earth Observing System project is implementing a rigorous program of absolute radiometric calibration for all optical sensors. Since a number of imaging instruments that provide output in terms of absolute radiance are calibrated at different sites, it is important to determine the errors that can be expected among calibration sites. Another question exists about the errors in the absolute knowledge of the exoatmospheric spectral solar irradiance.

Goetz, Alexander F. H.↗
NASA NTRS2001

Binaural Simulation Experiments in the NASA Langley Structural Acoustics Loads and Transmission Facility

A location and positioning system was developed and implemented in the anechoic chamber of the Structural Acoustics Loads and Transmission (SALT) facility to accurately determine the coordinates of points in three-dimensional space. Transfer functions were measured between a shaker source at two different panel locations and the vibrational response distributed over the panel surface using a scanning laser vibrometer. The binaural simulation test matrix included test runs for several locations of the measuring microphones, various attitudes of the mannequin, two locations of the shaker excitation and three different shaker inputs including pulse, broadband random, and pseudo-random. Transfer functions, auto spectra, and coherence functions were acquired for the pseudo-random excitation. Time histories were acquired for the pulse and broadband random input to the shaker. The tests were repeated with a reflective surface installed. Binary data files were converted to universal format and archived on compact disk.

Grosveld, Ferdinand W.↗
NASA NTRS2002

Gravitationally Redshifted Absorption Lines in the Burst Spectra of the Neutron Star in the X-Ray Binary EXO 0748-676

The most straightforward manner of determining masses and radii of neutron stars is by measuring the gravitational redshift of spectral lines produced in the neutron star photosphere; such a measurement would provide direct constraints on the mass-to-radius ratio of the neutron star, and therefore on the equation of state for neutron star matter. Using data taken with the Reflection Grating Spectrometer on board the XMM-Newton observatory we identify, for the first time, significant absorption lines in the spectra of 28 bursts of the low-mass X-ray binary EXO 0748-676. The most significant features are consistent with the Fe XXVI and XXV n=2-3 and O VIII n=1-2 transitions, with a redshift of z=0.35, identical within small uncertainties for the different transitions. This constitutes the first direct and unambiguous measurement of the gravitational redshift in a neutron star.

Cottoam, J.↗
NASA NTRS1993

Bladder Monitor

Diagnostic Ultrasound Corporation's Bladder Scan Monitor continuously records and monitors bladder fullness and alerts the wearer or caretaker when voiding is required. The sensor is held against the lower abdomen by a belt and connected to the monitor by a cable. The sensor obtains bladder volume data from sound waves reflecting off the bladder wall. The device was developed by Langley Research Center, the Ames Research Center and the NASA Technology Applications Team. It utilizes Langley's advanced ultrasound technology. It is licensed to the ARC for medical applications, and sublicensed to Diagnostics Ultrasound. Central monitoring systems are planned for the future.

Source record↗
NASA NTRS1999

Effect of color coding and subtraction on the accuracy of contrast echocardiography

BACKGROUND: Contrast echocardiography may be used to assess myocardial perfusion. However, gray scale assessment of myocardial contrast echocardiography (MCE) is difficult because of variations in regional backscatter intensity, difficulties in distinguishing varying shades of gray, and artifacts or attenuation. We sought to determine whether the assessment of rest myocardial perfusion by MCE could be improved with subtraction and color coding. METHODS AND RESULTS: MCE was performed in 31 patients with previous myocardial infarction with a 2nd generation agent (NC100100, Nycomed AS), using harmonic triggered or continuous imaging and gain settings were kept constant throughout the study. Digitized images were post processed by subtraction of baseline from contrast data and colorized to reflect the intensity of myocardial contrast. Gray scale MCE alone, MCE images combined with baseline and subtracted colorized images were scored independently using a 16 segment model. The presence and severity of myocardial contrast abnormalities were compared with perfusion defined by rest MIBI-SPECT. Segments that were not visualized by continuous (17%) or triggered imaging (14%) after color processing were excluded from further analysis. The specificity of gray scale MCE alone (56%) or MCE combined with baseline 2D (47%) was significantly enhanced by subtraction and color coding (76%, p<0.001) of triggered images. The accuracy of the gray scale approaches (respectively 52% and 47%) was increased to 70% (p<0.001). Similarly, for continuous images, the specificity of gray scale MCE with and without baseline comparison was 23% and 42% respectively, compared with 60% after post processing (p<0.001). The accuracy of colorized images (59%) was also significantly greater than gray scale MCE (43% and 29%, p<0.001). The sensitivity of MCE for both acquisitions was not altered by subtraction. CONCLUSION: Post-processing with subtraction and color coding significantly improves the accuracy and specificity of MCE for detection of perfusion defects.

Multicenter Study↗
NASA NTRS1990

Reflected Sunlight Reduction and Characterization for a Deep-Space Optical Receiver Antenna (DSORA)

A baffle system for the elimination of first-order specular and diffuse reflection of sunlight from the sunshade of a deep-space optical receiver telescope is presented. This baffle system consists of rings of 0.5cm blades spaced 2.5 cm apart on the walls of GO hexagonal sunshade tubes that combine to form the telescope sunshade. The shadow cast by the blades, walls, and rims of the tubes prevent all first-order reflections of direct sunlight from reaching the primary mirror of the telescope. A reflection model of the sunshade without baffles is also presented for comparison. Since manufacturers of absorbing surfaces do not measure data near grazing incidence, the reflection properties at anticipated angles of incidence must be characterized. A description of reflection from matte surfaces in term of bidirectional reflection distribution function (BRDF) is presented along with a discussion of measuring BRDF near grazing incidence.

Clymer, B. D.↗
NASA NTRS2005

Mars Express OMEGA Observations over Terra Meridiani

The OMEGA hyperspectral imager (0.35 to 5.08 micrometers) covered the hematite-bearing plains and underlying etched terrains of Terra Meridiani during several orbits with spatial resolutions ranging from several hundred meters to approximately 2 km. We extracted and analyzed surface reflectance spectra from OMEGA data for the approximately 864,000 square kilometers surrounding the Opportunity site. In this paper we focus on analysis of OMEGA orbit 485 data for the plains and etched terrains located to the northeast of the Opportunity landing site.

Arvidson, R. E.↗
NASA NTRS2004

Daytime Water Detection by Fusing Multiple Cues for Autonomous Off-Road Navigation

Detecting water hazards is a significant challenge to unmanned ground vehicle autonomous off-road navigation. This paper focuses on detecting the presence of water during the daytime using color cameras. A multi-cue approach is taken. Evidence of the presence of water is generated from color, texture, and the detection of reflections in stereo range data. A rule base for fusing water cues was developed by evaluating detection results from an extensive archive of data collection imagery containing water. This software has been implemented into a run-time passive perception subsystem and tested thus far under Linux on a Pentium based processor.

COMPONENT REPORTS↗
NASA NTRS2004

Evaluation of Droplet Splashing Algorithm in LEWICE 3.0

The Icing Branch at NASA Glenn Research has developed a computer program to simulate ice formation on the leading edge of an aircraft wing during flight through cold, moist air. As part of the branch's current research, members have developed software known as LEWICE. This program is capable of predicting the formation of ice under designated weather conditions. The success of LEWICE is an asset to airplane manufacturers, ice protection system manufacturers, and the airline industry. Simulations of ice formation conducted in the tunnel and in flight is costly and time consuming. However, the danger of in-flight icing continues to be a concern for both commercial and military pilots. The LEWICE software is a step towards inexpensive and time efficient prediction of ice collection. In the most recent version of the program, LEWICE contains an algorithm for droplet splashing. Droplet splashing is a natural occurrence that causes accumulation of ice on aircraft surfaces. At impingement water droplets lose a portion of their mass to splashing. With part of each droplet joining the airflow and failing to freeze, early versions of LEWICE without the splashing algorithm over-predicted the collection of ice on the leading edge. The objective of my project was to determine whether the revised version of LEWICE accurately reflected the ice collection data obtained from the Icing Research Tunnel (IRT). The experimental data from the IRT was collected by Mark Potapczuk in January, March and July of 2001 and April and December of 2002. Experimental data points were the result of ice tracings conducted shortly after testing in the tunnel. Run sheets, which included a record of velocity, temperature, liquid water content and droplet diameter, served as the input of the LEWICE computer program. Parameters identical to the tunnel conditions were used to run LEWICE 2.0 and LEWICE 3.0. The results from IRT and versions of LEWICE were compared graphically. After entering the raw experimental data and computer output into a spread sheet, I mapped each ice formation onto a clean airfoil. The LEWICE output provided the data points to graphically depict ice formations developed by the program. weather conditions of runs conducted in January 2001, it was evident that the splashing algorithm of LEWICE 3.0 predicts ice formations more accurately than LEWICE 2.0. Especially at conditions with droplet size between 80 and 160 microns, the splashing algorithm of the new LEWICE version compensated for the loss of droplet mass as a result of splashing. In contrast, LEWICE 2.0 consistently over-predicted the mass of the ice in conditions with droplet size exceeding 80 microns. This evidence confirms that changes made to algorithms of LEWICE 3.0 have increased the accuracy of predicting ice collection.

Homenko, Hilary N.↗
NASA NTRS2005

Case Study of the Space Shuttle Cockpit Avionics Upgrade Software

The purpose of the Space Shuttle Cockpit Avionics Upgrade project was to reduce crew workload and improve situational awareness. The upgrade was to augment the Shuttle avionics system with new hardware and software. An early version of this system was used to gather human factor statistics in the Space Shuttle Motion Simulator of the Johnson Space Center for one month by multiple teams of astronauts. The results were compiled by NASA Ames Research Center and it was was determined that the system provided a better than expected increase in situational awareness and reduction in crew workload. Even with all of the benefits nf the system, NASA cancelled the project towards the end of the development cycle. A major success of this project was the validation of the hardware architecture and software design. This was significant because the project incorporated new technology and approaches for the development of human rated space software. This paper serves as a case study to document knowledge gained and techniques that can be applied for future space avionics development efforts. The major technological advances were the use of reflective memory concepts for data acquisition and the incorporation of Commercial off the Shelf (COTS) products in a human rated space avionics system. The infused COTS products included a real time operating system, a resident linker and loader, a display generation tool set, and a network data manager. Some of the successful design concepts were the engineering of identical outputs in multiple avionics boxes using an event driven approach and inter-computer communication, a reconfigurable data acquisition engine, the use of a dynamic bus bandwidth allocation algorithm. Other significant experiences captured were the use of prototyping to reduce risk, and the correct balance between Object Oriented and Functional based programming.

Ferguson, Roscoe C.↗
NASA NTRS1994

Directional emittance surface measurement system and process

Apparatus and process for measuring the variation of directional emittance of surfaces at various temperatures using a radiometric infrared imaging system. A surface test sample is coated onto a copper target plate provided with selective heating within the desired incremental temperature range to be tested and positioned onto a precision rotator to present selected inclination angles of the sample relative to the fixed positioned and optically aligned infrared imager. A thermal insulator holder maintains the target plate on the precision rotator. A screen display of the temperature obtained by the infrared imager, and inclination readings are provided with computer calculations of directional emittance being performed automatically according to equations provided to convert selected incremental target temperatures and inclination angles to relative target directional emittance values. The directional emittance of flat black lacquer and an epoxy resin measurements obtained are in agreement with the predictions of the electromagnetic theory and with directional emittance data inferred from directional reflectance measurements made on a spectrophotometer.

Puram, Chith K.↗
NASA NTRS2007

The Orbiting Carbon Observatory Mission: Watching the Earth Breathe Mapping CO2 from Space

Approach: Collect spatially resolved, high resolution spectroscopic observations of CO2 and O2 absorption in reflected sunlight. Use these data to resolve spatial and temporal variations in the column averaged CO2 dry air mole fraction, X(sub CO2) over the sunlit hemisphere. Employ independent calibration and validation approaches to produce X(sub CO2) estimates with random errors and biases no larger than 1-2 ppm (0.3-0.5%) on regional scales at monthly intervals.

three channel grating spectrometry↗