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At least 1,621 records · Page 90
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NASA NTRS1993

Evaluation of two January - June 1992 ERS-1 AMI wind vector data sets

A Jan. - Jun. 1992 10 m height wind vector field was computed with the CMOD2 model function. Freilich and Dunbar used ESA measurements of AMI (Active Microwave Instrument) sigma-naught to derive a refined model function and to produce an alternate Jan. - Jun. 1992 10 m height wind vector field, named FD data. The ESA and FD model functions and algorithms were substantially different. The FD wind vectors were in better agreement with the climatological mean wind field and with moored buoy wind measurements. The average correlation coefficients between monthly mean and daily averaged FD and moored buoy matchups of the Cartesian wind components were 0.84 and 0.74, respectively. The average root mean square differences between the monthly mean and daily averaged FD and moored buoy matchups of the Cartesian wind components were 1.25 and 3.0 m/s, respectively.

Halpern, D.↗
NASA NTRS1993

The effects of instructional sets on reactions to and performance on an intelligent tutoring system

The effects of a contextual factor, i.e., task instructions, on performance on and reactions to an Intellegent Tutoring System (ITS) training Remote Manipulator System (RMS) tasks were examined. The results supported the first prediction that task instructions could be used to successfully induce a mastery versus an achievement orientation. Previous research suggests that a mastery orientation can result in beneficial effects on learning and performance of complex tasks. Furthermore, the results supported the second prediction that a mastery orientation would have beneficial effects on learning and performance as well as affective and cognitive reactions to the ITS tasks. Moreover, the results indicated that a mastery orientation was especially beneficial for the more complex ITS tasks and later in task practice, i.e., when a task was performed for the second time. A mastery orientation is posited to have its beneficial effects by focusing more effort and attention on task performance. Conclusions are drawn with some caution due to the small number of subjects, although the results for these subjects were consistent across multiple trials and multiple measures of performance. ITS designers are urged to consider contextual factors such as task instructions and feedback in terms of their potential to induce a mastery versus an achievement orientation.

Johnson, Debra Steele↗
NASA NTRS1994

Truncated Gaussians as tolerance sets

This work focuses on the use of truncated Gaussian distributions as models for bounded data measurements that are constrained to appear between fixed limits. The authors prove that the truncated Gaussian can be viewed as a maximum entropy distribution for truncated bounded data, when mean and covariance are given. The characteristic function for the truncated Gaussian is presented; from this, algorithms are derived for calculation of mean, variance, summation, application of Bayes rule and filtering with truncated Gaussians. As an example of the power of their methods, a derivation of the disparity constraint (used in computer vision) from their models is described. The authors' approach complements results in Statistics, but their proposal is not only to use the truncated Gaussian as a model for selected data; they propose to model measurements as fundamentally in terms of truncated Gaussians.

Cozman, Fabio↗
NASA NTRS1994

The organic surface of 5145 Pholus: Constraints set by scattering theory

No known body in the Solar System has a spectrum redder than that of object 5145 Pholus. We use Hapke scattering theory and optical constants measured in this laboratory to examine the ability of mixtures of a number of organic solids and ices to reproduce the observed spectrum and phase variation. The primary materials considered are poly-HCN, kerogen, Murchison organic extract, Titan tholin, ice tholin, and water ice. In a computer grid search of over 10 million models, we find an intraparticle mixture of 15% Titan tholin, 10% poly-HCN, and 75% water ice with 10-micrometers particles to provide an excellent fit. Replacing water ice with ammonia ice improves the fits significantly while using a pure hydrocarbon tholin, Tholin alpha, instead of Titan tholin makes only modest improvements. All acceptable fits require Titan tholin or some comparable material to provide the steep slope in the visible, and poly-HCN or some comparable material to provide strong absorption in the near-infrared. A pure Titan tholin surface with 16-micrometers particles, as well as all acceptable Pholus models, fit the present spectrophotometric data for the transplutonian object 1992 QB(sub 1). The feasibility of gas-phase chemistry to generate material like Titan tholin on such small objects is examined. An irradiated transient atmosphere arising from sublimating ices may generate at most a few centimeters of tholin over the lifetime of the Solar System, but this is insignificant compared to the expected lag deposit of primordial contaminants left behind by the sublimating ice. Irradiation of subsurface N2/CH4 or NH3/CH4 ice by cosmic rays may generate approximately 20 cm of tholin in the upper 10 m of regolith in the same time scale but the identity of this tholin to its gas-phase equivalent has not been demonstrated.

Wilson, Peter D.↗
NASA NTRS1994

Determination of tidal h Love number parameters in the diurnal band using an extensive VLBI data set

We use over a decade of geodetic Very Long Baseline Interferometry (VLBI) data to estimate parameters in a resonance expansion of the frequency dependence of the tidal h(sub 2) Love number within the diurnal band. The resonance is associated with the retrograde free core nutation (RFCN). We obtain a value for the real part of the resonance strength of (-0.27 +/- 0.03) x 10(exp -3); a value of -0.19 x 10(exp -3) is predicted theoretically. Uncertainties in the VLBI estimates of the body tide radial displacement amplitudes are approximately 0.5 mm (1.1 mm for the K1 frequency), but they do not yield sufficiently small Love number uncertainties for placing useful constraints on the frequency of the RFCN, given the much smaller uncertainties obtained from independent analyses using nutation or gravimetric data. We also consider the imaginary part of the tidal h(sub 2) Love number. The estimated imaginary part of the resonance strength is (0.00 +/- 0.02) x 10(exp -3). The estimated imaginary part of the nonresonant component of the Love number implies a phase angle in the diurnal tidal response of the Earth of 0.7 deg +/- 0.5 deg (lag).

Mitrovica, J. X.↗
NASA NTRS1995

Calculation of surface and top of atmosphere radiative fluxes from physical quantities based on ISCCP data sets. 1: Method and sensitivity to input data uncertainties

The largest uncertainty in upwelling shortwave (SW) fluxes (approximately equal 10-15 W/m(exp 2), regional daily mean) is caused by uncertainties in land surface albedo, whereas the largest uncertainty in downwelling SW at the surface (approximately equal 5-10 W/m(exp 2), regional daily mean) is related to cloud detection errors. The uncertainty of upwelling longwave (LW) fluxes (approximately 10-20 W/m(exp 2), regional daily mean) depends on the accuracy of the surface temperature for the surface LW fluxes and the atmospheric temperature for the top of atmosphere LW fluxes. The dominant source of uncertainty is downwelling LW fluxes at the surface (approximately equal 10-15 W/m(exp 2)) is uncertainty in atmospheric temperature and, secondarily, atmospheric humidity; clouds play little role except in the polar regions. The uncertainties of the individual flux components and the total net fluxes are largest over land (15-20 W/m(exp 2)) because of uncertainties in surface albedo (especially its spectral dependence) and surface temperature and emissivity (including its spectral dependence). Clouds are the most important modulator of the SW fluxes, but over land areas, uncertainties in net SW at the surface depend almost as much on uncertainties in surface albedo. Although atmospheric and surface temperature variations cause larger LW flux variations, the most notable feature of the net LW fluxes is the changing relative importance of clouds and water vapor with latitude. Uncertainty in individual flux values is dominated by sampling effects because of large natrual variations, but uncertainty in monthly mean fluxes is dominated by bias errors in the input quantities.

Zhang, Y.-C.↗
NASA NTRS1995

Evidence of seasonally dependent stratosphere-troposphere exchange and purging of lower stratospheric aerosol from a multiyear lidar data set

Tropospheric and lower stratospheric aerosol backscatter data obtained from a calibrated backscatter lidar at Pasadena, California (34 deg N latitude) over the 1984-1993 period clearly indicate tightly coupled aerosol optical properties in the upper troposphere and lower stratosphere in the winter and early spring, due to the active midlatitude stratospheric-tropospheric (ST) exchange processes occurring at this time of year. Lidar data indicate that during pre-Pinaturbo background conditions, the subsequent purging of the aerosol in the upper troposphere caused a significant reduction in the aerosol content throughout the 8 - 18 km altitude region in the early spring period. The post-Pinatubo evidence of intense exchange in the winter and early spring is a significant increase in the upper tropospheric aerosol content, such that the backscatter levels reach values nearly equivalent to the enhanced backscatter levels existing in the lower stratosphere. The calculated stratospheric mass extrusion rate is consistent with a 45-day lifetime of lower stratospheric aerosol during this part of the year, which implies that midlatitude ST exchange is a significant sink for stratospheric aerosol.

Menzies, Robert T.↗
NASA NTRS1994

Fatigue in operational settings: Examples from the aviation environment

The need for 24-h operations creates nonstandard and altered work schedules that can lead to cumulative sleep loss and circadian disruption. These factors can lead to fatigue and sleepiness and affect performance and productivity on the job. The approach, research, and results of the NASA Ames Fatigue Countermeasures Program are described to illustrate one attempt to address these issues in the aviation environment. The scientific and operational relevance of these factors is discussed, and provocative issues for future research are presented.

Rosekind, Mark R.↗
NASA NTRS1995

A data reduction, management, and analysis system for a 10-terabyte data set

Within 12 months a 5-year space-based research investigation with an estimated daily data volume of 10 to 15 gigabytes will be launched. Our instrument/analysis team will analyze 2 to 8 gigabytes per day from this mission. Most of these data will be spatial and multispectral collected from nine sensors covering the UV/Visible/NlR spectrum. The volume and diversity of these data and the nature of its analysis require a very robust reduction and management system. This paper is a summary of the systems requirements and a high-level description of a solution. The paper is intended as a case study of the problems and potential solutions faced by the new generation of Earth observation data support systems.

DeMajistre, R.↗
NASA NTRS1996

Interpretation of lidar and satellite data sets using a global photochemical model

The status in the beginning of the report period was that the existing General Circulation Model (GCM) was running with a chemistry module compiled for stratospheric simulation studies. The chemistry simulation was not working sufficiently in the troposphere and any tropospheric trace gas sources or dry deposition sinks were not yet incorporated. The current status concerning the chemistry module is that the chemistry simulation has been modified to also simulate the chemistry in the troposphere with resulting mixing ratios close to other model simulations as described in Olson et al. (1996). The mechanism to incorporate trace gas source and dry deposition sinks, testing for H202, CH300H, 03, HCHO, HN03, and N02, are incorporated and is currently being tested. Existing model and development versions include: the full GCM model, currently still running with the original stratospheric chemistry module; an off-line version of the GCM, i.e. wind and photolysis rates are pre-calculated and prescribed in read-in arrays; a box model version of the modified chemistry module for developments and first tests of new modifications; and a box model with the same chemistry simulated but flexible partitioning and integration methods for test purposes of those. The grantee's work focused mainly on three areas: trace gas sources and dry deposition; method to introduce a NO source instead of a NO(x) source; and investigating integration methods.

Chyba, Thomas↗
NASA NTRS1998

The Use of a Satellite Climatological Data Set to Infer Large Scale Three Dimensional Flow Characteristics

Ever since the first satellite image loops from the 6.3 micron water vapor channel on the METEOSAT-1 in 1978, there have been numerous efforts (many to a great degree of success) to relate the water vapor radiance patterns to familiar atmospheric dynamic quantities. The realization of these efforts is becoming evident with the merging of satellite derived winds into predictive models (Velden et al., 1997; Swadley and Goerss, 1989). Another parameter that has been quantified from satellite water vapor channel measurements is upper tropospheric relative humidity (UTH) (e.g., Soden and Bretherton, 1996; Schmetz and Turpeinen, 1988). These humidity measurements, in turn, can be used to quantify upper tropospheric water vapor and its transport to more accurately diagnose climate changes (Lerner et al., 1998; Schmetz et al. 1995a) and quantify radiative processes in the upper troposphere. Also apparent in water vapor imagery animations are regions of subsiding and ascending air flow. Indeed, a component of the translated motions we observe are due to vertical velocities. The few attempts at exploiting this information have been met with a fair degree of success. Picon and Desbois (1990) statistically related Meteosat monthly mean water vapor radiances to six standard pressure levels of the European Centre for Medium Range Weather Forecast (ECMWF) model vertical velocities and found correlation coefficients of about 0.50 or less. This paper presents some preliminary results of viewing climatological satellite water vapor data in a different fashion. Specifically, we attempt to infer the three dimensional flow characteristics of the mid- to upper troposphere as portrayed by GOES VAS during the warm ENSO event (1987) and a subsequent cold period in 1998.

Lerner, Jeffrey A.↗
NASA NTRS1998

Small Engine Technology (Set) Task 8 Aeroelastic Prediction Methods

AlliedSignal Engines, in cooperation with NASA LeRC, completed an evaluation of recently developed aeroelastic computer codes using test cases from the AlliedSignal Engines fan blisk database. Test data for this task includes strain gage, light probe, performance, and steady-state pressure information obtained for conditions where synchronous or flutter vibratory conditions were found to occur. Aeroelastic codes evaluated include the quasi 3-D UNSFLO (developed at MIT and modified to include blade motion by AlliedSignal), the 2-D FREPS (developed by NASA LeRC), and the 3-D TURBO-AE (under development at NASA LeRC). Six test cases each where flutter and synchronous vibrations were found to occur were used for evaluation of UNSFLO and FREPS. In addition, one of the flutter cases was evaluated using TURBO-AE. The UNSFLO flutter evaluations were completed for 75 percent radial span and provided good agreement with the experimental test data. Synchronous evaluations were completed for UNSFLO but further enhancement needs to be added to the code before the unsteady pressures can be used to predict forced response vibratory stresses. The FREPS evaluations were hindered as the steady flow solver (SFLOW) was unable to converge to a solution for the transonic flow conditions in the fan blisk. This situation resulted in all FREPS test cases being attempted but no results were obtained during the present program. Currently, AlliedSignal is evaluating integrating FREPS with our existing steady flow solvers to bypass the SFLOW difficulties. ne TURBO-AE steady flow solution provided an excellent match with the AlliedSignal Engines calibrated DAWES 3-D viscous solver. Finally, the TURBO-AE unsteady analyses also matched experimental observations by predicting flutter for the single test case evaluated.

Eick, Chris D.↗
NASA NTRS1998

Distributed Queries of Large Numerical Data Sets

We have extended a previously developed high-level data model, which combines numerical quantities and meta-data into a unified hybrid model, to distributed data. An elegant query language based on SQL is extended further to allow queries against such a distributed hybrid data base. The extension is realized by allowing statements in a non-SQL programming language to be embedded in SQL view definitions.

Nemes, Richard M.↗
NASA NTRS1999

Localized Ionospheric Particle Acceleration and Wave Acceleration of Auroral Ions: Amicist Data Set

Research supported by this grant covered two main topics: auroral ion acceleration from ELF-band wave activity, and from VLF-spikelet (lower hybrid solitary structure) wave activity. Recent auroral sounding rocket data illustrate the relative significance of various mechanisms for initiating auroral ion outflow. Two nightside mechanisms are shown in detail. The first mechanism is ion acceleration within lower hybrid solitary wave events. The new data from this two payload mission show clearly that: (1) these individual events are spatially localized to scales approximately 100 m wide perpendicular to B, in agreement with previous investigations of these structures, and (2) that the probability of occurrence of the events is greatest at times of maximum VLF wave intensity. The second mechanism is ion acceleration by broadband, low frequency electrostatic waves, observed in a 30 km wide region at the poleward edge of the arc. The ion fluxes from the two mechanisms are compared and it is shown that while lower hybrid solitary structures do indeed accelerate ions in regions of intense VLF waves, the outflow from the electrostatic ion wave acceleration region is dominant for the aurora investigated by this sounding rocket, AMICIST. The fluxes are shown to be consistent with DE-1 and Freja outflow measurements, indicating that the AMICIST observations show the low altitude, microphysical signatures of nightside auroral outflow. In this paper, we present a review of sounding rocket observations of the ion acceleration seen nightside auroral zone lower hybrid solitary structures. Observations from Topaz3, Amicist, and Phaze2 are presented on various spatial scales, including the two-point measurements of the Amicist mission. From this collection of observations, we will demonstrate the following characteristics of transverse ion acceleration (TAI) in LHSS. The ion acceleration process is narrowly confined to 90 degrees pitch angle, in spatially confined regions of up to a few hundred meters across B. The acceleration process does not affect the thermal core of the ambient distribution, and does not directly create a measurable effect on the ambient ion population outside the LHSS themselves. Within the LHSS region, it creates a high energy tail beginning at a few times the thermal ion speed. The ion acceleration events are closely associated with localized wave events. Accelerated ions bursts are also seen without a concurrent observation of a localized wave event, for two possible reasons. In some cases, the pitch angles of the accelerated tail ions are elevated above perpendicular; that is to say, the acceleration occurred below the observer and the mirror force has begun to act upon the distribution, moving it upward from the source. In other cases, the accelerated ion structure is spatially larger than the wave event structure, and the observation catches only the ion event. The occurrence rate of these ion acceleration events is related to the ambient environment in two ways: (1) its altitude dependence can be modelled with the parameter B(exp2)/n(sub e), (2) and it is highest in regions of intense VLF activity. The end result of this study of auroral ion acceleration processes is a manuscript entitled "Auroral Ion Acceleration from Lower Hybrid Solitary Structures: A Summary of Sounding Rocket Observations", by Lynch, Arnoldy, Kintner, Schuck, Bonnell, and Coffey. This manuscript has been submitted for publication to the Journal of Geophysical Research.

Lynch, Kristina A.↗
NASA NTRS1999

Small Engine Technology (SET) - Task 14 Axisymmetric Engine Simulation Environment

As part of the NPSS (Numerical Propulsion Simulation System) project, NASA Lewis has a goal of developing an U.S. industry standard for an axisymmetric engine simulation environment. In this program, AlliedSignal Engines (AE) contributed to this goal by evaluating the ENG20 software and developing support tools. ENG20 is a NASA developed axisymmetric engine simulation tool. The project was divided into six subtasks which are summarized below: Evaluate the capabilities of the ENG20 code using an existing test case to see how this procedure can capture the component interactions for a full engine. Link AE's compressor and turbine axisymmetric streamline curvature codes (UD0300M and TAPS) with ENG20, which will provide the necessary boundary conditions for an ENG20 engine simulation. Evaluate GE's Global Data System (GDS), attempt to use GDS to do the linking of codes described in Subtask 2 above. Use a turbofan engine test case to evaluate various aspects of the system, including the linkage of UD0300M and TAPS with ENG20 and the GE data storage system. Also, compare the solution results with cycle deck results, axisymmetric solutions (UD0300M and TAPS), and test data to determine the accuracy of the solution. Evaluate the order of accuracy and the convergence time for the solution. Provide a monthly status report and a final formal report documenting AE's evaluation of ENG20. Provide the developed interfaces that link UD0300M and TAPS with ENG20, to NASA. The interface that links UD0300M with ENG20 will be compatible with the industr,, version of UD0300M.

Miller, Max J.↗
NASA NTRS1999

Improving Assimilated Global Data Sets using TMI Rainfall and Columnar Moisture Observations

A global analysis that optimally combine observations from diverse sources with physical models of atmospheric and land processes can provide a comprehensive description of the climate systems. Currently, such data products contain significant errors in primary hydrological fields such as precipitation and evaporation, especially in the tropics. In this study, we show that assimilating precipitation and total precipitable water (TPW) retrievals derived from the TRMM Microwave Imager (TMI) improves not only the hydrological cycle but also key climate parameters such as clouds, radiation, and the large-scale circulation produced by the Goddard Earth Observing System (GEOS) data assimilation system (DAS). In particular, assimilating TMI rain improves clouds and radiation in areas of active convection, as well as the latent heating distribution and the large-scale motion field in the tropics, while assimilating TMI TPW heating distribution and the large-scale motion field in the tropics, while assimilating TMI TPW retrievals leads to reduced moisture biases and improved radiative fluxes in clear-sky regions. The improved analysis also improves short-range forecasts in the tropics. Ensemble forecasts initialized with the GEOS analysis incorporating TMI rain rates and TPW yield smaller biases in tropical precipitation forecasts beyond 1 day and better 500 hPa geopotential height forecasts up to 5 days. Results of this study demonstrate the potential of using high-quality space-borne rainfall and moisture observations to improve the quality of assimilated global data for climate analysis and weather forecasting applications

Hou, Arthur Y.↗
NASA NTRS1999

Longwave Radiative Flux Calculations in the TOVS Pathfinder Path A Data Set

A radiative transfer model developed to calculate outgoing longwave radiation (OLR) and downwelling longwave, surface flux (DSF) from the Television and Infrared Operational Satellite (TIROS) Operational Vertical Sounder (TOVS) Pathfinder Path A retrieval products is described. The model covers the spectral range of 2 to 2800 cm in 14 medium medium spectral bands. For each band, transmittances are parameterized as a function of temperature, water vapor, and ozone profiles. The form of the band transmittance parameterization is a modified version of the approach we use to model channel transmittances for the High Resolution Infrared Sounder 2 (HIRS2) instrument. We separately derive effective zenith angle for each spectral band such that band-averaged radiance calculated at that angle best approximates directionally integrated radiance for that band. We develop the transmittance parameterization at these band-dependent effective zenith angles to incorporate directional integration of radiances required in the calculations of OLR and DSF. The model calculations of OLR and DSF are accurate and differ by less than 1% from our line-by-line calculations. Also, the model results are within 1% range of other line-by-line calculations provided by the Intercomparison of Radiation Codes in Climate Models (ICRCCM) project for clear-sky and cloudy conditions. The model is currently used to calculate global, multiyear (1985-1998) OLR and DSF from the TOVS Pathfinder Path A Retrievals.

Mehta, Amita↗