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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Geologic mapping using Landsat MSS and TM images - Removing vegetation by modeling spectral mixtures

Semi-arid regions of the island of Hawaii and of the Tucson Mountains, AZ, having less than 50 percent green vegetation cover were mapped into rock/soil types by first identifying spectral mixtures of vegetation and rock/soil, and then removing the vegetation information. Landsat MSS images were used for Hawaii, and a Landsat TM image was used for the Tucson Mountains. Following analysis of the images field transects were done in test areas to determine percent vegetation cover and vegetation community characteristics, and to observe rock and soil types. For both Hawaii and the Tucson Mountains 20 percent or more of green vegetation caused potential misidentification of the rock/soil units unless spectral mixing was taken into account.

Adams, J. B.↗
NASA NTRS1987

A simple spectral model of the dynamics of the Venus ionosphere

A two-dimensional model of the ionosphere of Venus has been constructed by expanding pertinent quantities in Legendre polynomials. The model is simplified by including only a single ion species, O(+). Horizontal plasma flow velocity and plasma density have been calculated as a coupled system. The calculated plasma flow velocity is found to be in good agreement with observations and the results of earlier studies. Solar zenith angle dependence of plasma density, particularly on the nightside, shows some features which differ from results of earlier studies and observed values. Effects of raising or lowering the ionopause height and changing the nightside neutral atmosphere have been discussed.

Singhal, R. P.↗
NASA NTRS1988

X-ray spectral models of Galactic bulge sources - The emission-line factor

Current difficulties in finding unique and physically meaningful models for the X-ray spectra of Galactic bulge sources are exacerbated by the presence of strong, variable emission and absorption features that are not resolved by the instruments observing them. Nine Einstein solid state spectrometer (SSS) observations of five Galactic bulge sources are presented for which relatively high resolution objective grating spectrometer (OGS) data have been published. It is found that in every case the goodness of fit of simple models to SSS data is greatly improved by adding line features identified in the OGS that cannot be resolved by the SSS but nevertheless strongly influence the spectra observed by SSS.

Vrtilek, S. D.↗
NASA NTRS1988

A simulation of the winter and summer circulations with the NMC Global Spectral Model

The medium range forecast model of the NMC has been integrated to produce winter and summer simulations. It is found that the model climatology is similar to that of the observed atmosphere as well as climatologies of other general circulation models. The stationary and transient features of the model circulation are described, including both tropical and extratropical regions. The model hydrological cycle, radiative balance, and surface heat budget are discussed. Comparison with observations shows that the model is colder than that observed in the troposphere and cools in the lower stratosphere in the tropics and near the poles in both simulations. It is suggested that the upper branch of the Hadley cell is poorly simulated in the integrated model. The simulations are in reasonable agreement with the observations in sea level pressure, the structure of the tropospheric zonal jets, and the winter hemispheric stationary waves.

Kinter, J. L., III↗
NASA NTRS1991

Observing system simulation experiments for the laser atmospheric wind sounder using global spectral model

Fundamental to improving the understanding of the total Earth system are increased and improved observations. In the coming decade several spaceborne instrumented platforms will be constructed and implemented. These platforms will, in large, be housing the NASA Earth Observing System (EOS) instrument suite. One of the proposed instruments is a wind profiling system which is currently referred to as the Laser Atmospheric Wind Sounder (LAWS). This instrument will use a CO2 Doppler lidar wind profiler to give wind measurements with a vertical and horizontal resolution which has yet to be seen globally. The LAWS instrument is now a candidate for launch on a NASA EOS-B platform and is fundamental to increasing our understanding of Earth system science. The LAWS data sets will form an integral component of the temporally continuous data base needed for research of the coupled climate systems. This instrument's observations will aid in giving an improved description of the atmospheric circulation, including the transports of energy, momentum, moisture, trace gases, and aerosols. Also, the wind data will be assimilated and used as the initial state for many global forecast models at various operational centers. Results of system simulation experiments are discussed, and future experiments are described.

Rohaly, Gregg↗
NASA NTRS1993

Impact of increased TOVS signal on the NMC global spectral model - A tropical-plume case study

Temperature and moisture signals are extracted from operationally available TOVS channel radiances for a tropical plume that developed over the North Pacific in January 1989, and are inserted into the NMC's operational medium-range forecast model. Several 48-h forecasts are made to test the impact of the additional information. It is shown, at least within a single tropical plume event, that there is still unutilized information within operational TOVS satellite observations. This information resides in the moisture channels and within small-amplitude, but horiontally coherent, thermal features. Perturbed upper-tropospheric relative humidity patterns are smoother and more consistent with satellite imagery than is the historical forecast.

Mcguirk, James P.↗
NASA NTRS1997

Spectral Models of Neutron Star Magnetospheres

We revisit the association of unidentified Galactic plane EGRET sources with tracers of recent massive star formation and death. Up-to-date catalogs of OB associations, SNR's, young pulsars, H2 regions and young open clusters were used in finding counterparts for a recent list of EGRET sources. It has been argued for some time that EGRET source positions are correlated with SNR's and OB associations as a class; we extend such analyses by finding additional counterparts and assessing the probability of individual source identifications. Among the several scenarios relating EGRET sources to massive stars, we focus on young neutron stars as the origin of the gamma-ray emission. The characteristics of the candidate identifications are compared to the known gamma-ray pulsar sample and to detailed Galactic population syntheses using our outer gap pulsar model of gamma-ray emission. Both the spatial distribution and luminosity function of the candidates are in good agreement with the model predictions; we infer that young pulsars can account for the bulk of the excess low latitude EGRET sources. We show that with this identification, the gamma-ray point sources provide an important new window into the history of recent massive star death in the solar neighborhood.

Romani, Roger W.↗
NASA NTRS2002

Comparing Satellite Rainfall Estimates with Rain-Gauge Data: Optimal Strategies Suggested by a Spectral Model

Validation of satellite remote-sensing methods for estimating rainfall against rain-gauge data is attractive because of the direct nature of the rain-gauge measurements. Comparisons of satellite estimates to rain-gauge data are difficult, however, because of the extreme variability of rain and the fact that satellites view large areas over a short time while rain gauges monitor small areas continuously. In this paper, a statistical model of rainfall variability developed for studies of sampling error in averages of satellite data is used to examine the impact of spatial and temporal averaging of satellite and gauge data on intercomparison results. The model parameters were derived from radar observations of rain, but the model appears to capture many of the characteristics of rain-gauge data as well. The model predicts that many months of data from areas containing a few gauges are required to validate satellite estimates over the areas, and that the areas should be of the order of several hundred km in diameter. Over gauge arrays of sufficiently high density, the optimal areas and averaging times are reduced. The possibility of using time-weighted averages of gauge data is explored.

Bell, Thomas L.↗
NASA NTRS2007

Tracing the Jet Contribution to the Mid-IR over the 2005 Outburst of GRO J1655-40 via Broadband Spectral Modeling

We present new results from a multi-wavelength (radio/infrared/optical/X-ray) study of the black hole Xray binary GRO 51655-40 during its 2005 outburst. We detected, for the first time, mid-infrared emission at 24 micron from the compact jet of a black hole X-ray binary during its hard state, when the source shows emission from a radio compact jet, as well as a strong non-thermal hard X-ray component. These detections strongly constrain the optically thick part of the synchrotron spectrum of the compact jet, which is consistent with it being flat over 4 orders of magnitude in frequency. Moreover, using this unprecedented coverage, and especially thanks to the new Spitzer observations, we can test broadband disk and jet models during the hard state. Two of the hard-state broadband spectra are reasonably well fitted using a jet model with parameters that overall are similar to those previously found for Cyg X-1 and GX 339-4. Differences are also present; most notably, the jet power in GRO J1655-40 appears to be a factor of at least approximately 3-5 higher (depending on the distance) than those of Cyg X-1 and GX-339-4 at comparable disk luminosities. Furthermore, a few discrepancies between the model and the data, previously not found for the other two black hole systems for which there was no mid-IR/IR and optical coverage, are evident, and will help to constrain and refine theoretical models.

Migliari, S.↗
NASA NTRS2000

Atomic Data in X-Ray Astrophysics

With the launches of the Chandra X-ray Observatory (CXO) and the X-ray Multimirror Mission (XMM) and the upcoming launch of the Japanese mission ASTRO-E, high resolution X-ray spectroscopy of cosmic sources has begun. Early, deep observations of three stellar coronal sources will provide not only invaluable calibration data, but will also give us benchmarks for the atomic data under collisional equilibrium conditions. Analysis of the Chandra X-ray Observatory data, and data from other telescopes taken simultaneously, for these stars is ongoing as part of the Emission Line Project. Goals of the Emission Line Project are: (1) to determine and verify accurate and robust diagnostics and (2) to identify and prioritize issues in fundamental spectroscopy which will require further theoretical and/or laboratory work. The Astrophysical Plasma Emission Database will be described in some detail, as it is introducing standardization and flexibility into X-ray spectral modeling. Spectral models of X-ray astrophysical plasmas can be generally classified as dominated by either collisional ionization or by X-ray photoionization. While the atomic data needs for spectral models under these two types of ionization are significantly different, there axe overlapping data needs, as I will describe. Early results from the Emission Line Project benchmarks are providing an invaluable starting place, but continuing work to improve the accuracy and completeness of atomic data is needed. Additionally, we consider the possibility that some sources will require that both collisional ionization and photoionization be taken into account, or that time-dependent ionization be considered. Thus plasma spectral models of general use need to be computed over a wide range of physical conditions.

Brickhouse, N. S.↗
NASA NTRS1994

Transport characteristics of a finite-difference dynamics model combined with a spectral transport model of the middle atmosphere

A three-dimensional off-line spectral transport model has been combined with a global, mechanistic, finite-difference dynamics model of the middle atmosphere in order to study transport and photochemistry in the middle atmosphere for specific, observed episodes. In this paper, the basic transport characteristics of the combined models are examined, first using steady, idealized flow fields and second using time-dependent flow fields closely related to observed atmospheric behavior. Transport conducted with the combined models is found to compare favorably with transport conducted on-line in the dynamics model, given appropriate time averaging of the flow fields and suitable choice of artificial diffusion.

Duncan, T.↗
NASA NTRS1980

A seasonal verification of the Suits spectral reflectance model for wheat

Variables that characterize wheat canopies for the Suits Model and spectral bidirectional reflectance measurements in the 450 to 1350 nm interval were determined approximately weekly throughout the growing season for two cultivars of wheat that achieved maximum leaf area index of 5.3 and 10.8. The Suits Model plant variables were tabulated and experimental reflectance measurements were compared with the model predictions in the wavelength interval from 500 to 1150 nm at 50 nm increments for 17 measurement dates. The seasonal average coefficient of determination, r squared, was 0.88 between the Suits spectral bidirectional reflectance model and field-measured reflectance data. Poorest agreement was found very early and very late in the growing season, possibly due to low green plant biomass and incomplete ground cover.

Lemaster, E. W.↗
DOE OSTI2021

Modeling Spectrally-Selective Reflection for Thermal Management in Monofacial and Bifacial Modules

Parasitic absorption in photovoltaic modules is a major source of waste heat, which drives operating temperatures 20-30K above ambient. Spectrally-selective sub-bandgap reflection can reduce parasitic absorption, thereby improving module efficiency and power output. Here, we investigate the performance of 1-D spectrally-selective mirrors in monofacial Al BSF and PERC modules, and bifacial PERC modules. In monofacial modules, these mirrors offer >1.2% increase in energy yield compared to single-layer anti-reflection coatings, while cooling by over 1K on average. Mirrors reduced bifacial module parasitic absorption by up to 34 W/m2 out of 1240 W/m2 incident.

41 EE - Solar Energy Technologies Office (EE-4S)↗
NASA NTRS1998

Radiance Covariance and Climate Models

Spectral Empirical Orhtogonal Functions (EOFs) derived from the covariance of satellite radiance spectra may be interpreted in terms of the vertical distribution of the covariance of temperature, water vapor, and clouds. The purpose of the investigation is to demonstrate the important constraints that resolved spectral radiances can place upon climate models.

Spectral Empirical Orthogonal Functions EOFs radia↗
NASA NTRS1997

Nonlinear Spectral Mixture Modeling of Lunar Multispectral: Implications for Lateral Transport

Linear and nonlinear spectral mixture models applied to Clementine multispectral images of the Moon result in roughly similar spatial distributions of endmember abundances. However, there are important differences in the absolute values of the predicted abundances. The magnitude of these differences and the implications for understanding geological processes are investigated across a geologic contact between mare and highland in the Grimaldi Basin on the western nearside of the Moon. Vertical and lateral mass transport due to impact cratering has redistributed mare and highland materials across the contact, creating a gradient in composition. Solutions to linear and nonlinear spectral mixture models for identical spectral endmembers of mare, highland, and fresh crater materials are compared across this simple geologic contact in the Grimaldi Basin. Profiles of mare abundance across the contact are extracted and compared quantitatively. Profiles from the linear mixture models indicate that the geologic contact has an average mare abundance of 60%, and the compositional boundary is asymmetric with more mare transported onto the highland side of the contact than highland onto the mare side of the contact. In contrast the nonlinear abundance profiles indicate that the geologic contact has an average mare abundance of 50%, and the compositional boundary is remarkably symmetric. Given the expectation that materials will be intimately mixed on the surface of the Moon, and that the asymmetries implied by the linear model are not consistent with our understanding of lunar surface processes, the nonlinear spectral mixture model is preferred and should be applied whenever quantitative abundance information is required. The remarkable symmetry in the compositional gradients across this contact indicate that lateral mass transport dominates over vertical transport at this boundary.

Mustard, John F.↗
NASA NTRS1994

Tracer evolution in winds generated by a global spectral mechanistic model

The lower boundary of a spectral mechanistic model is prescribed with 100 hPa geopotentials, and its performance during a November 1989 through March 1990 integration is compared with National Meteorological Center observations. Although the stratopause temperatures quickly become biased near the pole in both hemispheres, the model develops a residual mean circulation which shows significant descent over the winter pole and ascent in the tropics and over the summer pole at pressures less than 10 hPa. The daily correspondence of observed to modeled features in the upper stratosphere and mesosphere degrades after one month. However, the long-term variability qualitatively follows the observations. The results of off-line transport experiments are also described. A passive tracer is instantaneously injected into the flow over the poles and evolves in a manner which is consistent with the residual mean circulation. It demonstrates a significant cross-equatorial flux in the mesosphere near solstice, and air which originates in the southern hemisphere polar mesosphere can be found descending deep into the nothern polar stratosphere at the end of the integration. Nitrous oxide is also transported, and its ability to act as a dynamical tracer is evaluated by comparison to the evolution of the passive tracer.

Nielsen, J. E.↗
DOE OSTI2020

The Performance of a Spectral Wave Model at Predicting Wave Farm Impacts

For renewable ocean wave energy to support global energy demands, wave energy converters (WECs) will likely be deployed in large numbers (farms), which will necessarily change the nearshore environment. Wave farm induced changes can be both helpful (e.g., beneficial habitat and coastal protection) and potentially harmful (e.g., degraded habitat, recreational, and commercial use) to existing users of the coastal environment. It is essential to estimate this impact through modeling prior to the development of a farm, and to that end, many researchers have used spectral wave models, such as Simulating WAves Nearshore (SWAN), to assess wave farm impacts. However, the validity of the approaches used within SWAN have not been thoroughly verified or validated. Herein, a version of SWAN, called Sandia National Laboratories (SNL)-SWAN, which has a specialized WEC implementation, is verified by comparing its wave field outputs to those of linear wave interaction theory (LWIT), where LWIT is theoretically more appropriate for modeling wave-body interactions and wave field effects. The focus is on medium-sized arrays of 27 WECs, wave periods, and directional spreading representative of likely conditions, as well as the impact on the nearshore. A quantitative metric, the Mean Squared Skill Score, is used. Results show that the performance of SNL-SWAN as compared to LWIT is “Good” to “Excellent”.

environmental impacts↗