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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Transforming ground-measured reflectances to radiances measured by various space sensors through clear and turbid atmospheres

The influence on the ratios of the ground measured reflectances in the range 0.8-1.1 microns to those in the range 0.6-0.7 microns of the intervening atmosphere and the sensor response are investigated over a typical range of remote sensing conditions. A simulation of the influences of clear and turbid atmospheres is developed, and their effects on Landsat MSS band 7 to band 5 ratios are determined for Avondale loam and stressed and unstressed vegetation. Results show that for dry loam the differences between the band 7 to band 5 ratios as determined from space and ground level measurements is 2.3% for clear and 5.6% for turbid atmospheric conditions, while for wet loams the differences are 10.4% and 29.5%. It is concluded that the effect of the atmosphere on band ratios for vegetation indicates that atmospheric conditions may delay the discrimination of stressed from unstressed vegetation by 3 to 7 days. The influence of the atmosphere is found to increase for oblique angle observations, and the path radiance and the change in path radiance are greater in the 0/180 degree azimuth than in the 90/270 azimuth.

Slater, P. N.↗
NASA NTRS1982

Atmospheric Backscatter Model Development for CO Sub 2 Wavelengths

The results of investigations into the problems of modeling atmospheric backscatter from aerosols, in the lowest 20 km of the atmosphere, at CO2 wavelengths are presented, along with a summary of the relevant aerosol characteristics and their variability, and a discussion of the measurement techniques and errors involved. The different methods of calculating the aerosol backscattering function, both from measured aerosol characteristics and from optical measurements made at other wavelengths, are discussed in detail, and limits are placed on the accuracy of these methods. The effects of changing atmospheric humidity and temperature on the backscatter are analyzed and related to the actual atmosphere. Finally, the results of modeling CO2 backscatter in the atmosphere are presented and the variation with height and geographic location discussed, and limits placed on the magnitude of the backscattering function. Conclusions regarding modeling techniques and modeled atmospheric backscatter values are presented in tabular form.

Deepak, A.↗
NASA NTRS1983

Atmospheric definition for Shuttle aerothermodynamic investigations

A procedure has been developed to estimate the freestream atmospheric properties along the Shuttle trajectory during atmospheric re-entry. The procedure utilizes measurement data obtained by NASA, NOAA, and the Air Force, and model data for regions where measured data are nonexistent. The results obtained are used to determine the best atmosphere-relative trajectory parameters during re-entry and to allow for an evaluation of the aerodynamic and aerothermodynamic characteristics of the Shuttle. A discussion of the method employed by the Langley Atmospheric Information Retrieval System, which is a computer code for the determination of atmospheric parameters, is presented. Results obtained from the first two Shuttle flights, STS-1 and STS-2, are also given with applications of these atmospheric parameters.

Price, J. M.↗
NASA NTRS1983

The thermal structure of the atmospheric surface boundary layer on Mars as modified by the radiative effect of aeolian dust

A computational simulation, based on Mariner 9 data, was performed for the thermal characteristics of the Martian atmospheric surface boundary layer in clear and dust-filled conditions. A radiative transfer model consisting of the atmospheric enthalpy rate equation, the radiative flux integrated over the 0.2-50 microns, the solid angle interval, and 0.50 km altitudes, broken into 52 levels. Mariner 9 IR data for CO2 absorption lines were included in the form of a temperture-dependent equation, while the line-widths were interpreted in terms of the pressure dependene as well as temperature. The lines covered the regions from 1-50 microns and varying conditions of dust content in the atmosphere. Attention was given to the thermal coupling between the ground and the atmosphere. It was found that convective heat exchange develops quickly due to radiative heating of the Martian desert surface, but does not cool the surface because of the attenuated atmosphere. The model predictd the 100 K temperature variations in the dusty atmosphere, as observed by the Viking thermal mapper. It is suggested that radiative flux convergence is as important as convection at equivalent efficiencies.

Pallmann, A. J.↗
NASA NTRS1984

Middle Atmospheric Science

Scientific objectives of middle atmosphere research in the 1990's are discussed. Radiative, chemical and dynamical processes in the middle atmosphere; long term evolution of middle atmosphere chemistry; and the interannual variability of middle atmosphere dynamics and transport are among the topics discussed. Observational requirements relative to atmospheric processes, atmospheric chemistry, interannual variability, and the upper mesosphere and lower thermosphere are given.

Gille, J. C.↗
NASA NTRS1984

Impact of atmospheric uncertainties and viscous interaction effects on the performance of aeroassisted orbital transfer vehicles

Simulations of aerobraking trajectories of aeroassisted orbital transfer vehicles (AOTV's) returning from geosynchronous orbit were analyzed to examine the effects of high-altitude viscous interactions and off-nominal atmospheres on AOTV return weight, heating, and loads performance. Viscous interaction effects encountered at high altitudes had little detrimental effect on the return weight capabilities for AOTV's representing a range of lift/drag ratios. Most of the AOTV return weight increase over an all-propulsive OTV occurred for a low lift/drag ratio. Smaller increases in return weight were observed for higher lift/drag ratios, at the expense of significantly higher heating and aerodynamic loads. Off-nominal atmospheres based on Shuttle-derived data and multipliers on a U.S. Standard Atmosphere were considered. AOTV's intended for entry under standard atmospheric conditions either deorbited during the pass through the off-nominal atmospheres or missed the target phasing orbit by wide margins. The AOTV's could successfully negotiate these atmospheres when new bank-angle histories were implemented with little loss and sometimes with a gain in return weight.

Talay, T. A.↗
NASA NTRS1984

Atmospheric limitations to clock synchronization at microwave frequencies

Clock synchronization schemes utilizing microwave signals that pass through the Earth's atmosphere are ultimately limited by our ability to correct for the variable delay imposed by the atmosphere. The atmosphere is non-dispersive at microwave frequencies and imposes a delay of roughly 8 nanosec times the cosecant of the elevation angle. This delay is composed of two parts, the delay due to water vapor molecules (i.e., the wet delay), and the delay due to all other atmospheric constituents (i.e., the dry delay). Water vapor contributes approximately 5 to 10% of the total atmospheric delay but is highly variable, not well mixed, and difficult to estimate from surface air measurements. However, the techniques of passive remote sensing using microwave radiometry can be used to estimate the line of sight delay due to water vapor with potential accuracies of 10 to 20 picosec. The devices that are used are called water vapor radiometers and simply measure the power emitted by the water vapor molecule at the 22.2 GHz spectral line. An additional power measurement is usually included at 31.4 GHz in order to compensate for the effect of liquid water (e.g., clouds). The dry atmosphere is generally in something close to hydrostatic equilibrium and its delay contribution at zenith can be estimated quite well from a simple barometric measurement. At low elevation angles one must compensate for refractive bending and possible variations in the vertical refractivity profile. With care these effects can be estimated with accuracies on the order of 30 picosec down to elevation angles of 10 degree.

Resch, G. M.↗
NASA NTRS1985

Atmospheric Effect on Remote Sensing of the Earth's Surface

Radiative transfer theory (RT) for an atmosphere with a nonuniform surface is the basis for understanding and correcting for the atmospheric effect on remote sensing of surface properties. In the present work the theory is generalized and tested successfully against laboratory and field measurements. There is still a need to generalize the RT approximation for off-nadir directions and to take into account anisotropic reflectance at the surface. The reflectance at the surface. The adjacency effect results in a significant modification of spectral signatures of the surface, and therefore results in modification of classifications, of separability of field classes, and of spatial resolution. For example, the 30 m resolution of the Thematic Mapper is reduced to 100 m by a hazy atmosphere. The adjacency effect depends on several optical parameters of aerosols: optical thickness, depth of aerosol layer, scattering phase function, and absorption. Remote sensing in general depends on these parameter, not just adjacency effects, but they are not known well enough for making accurate atmospheric corrections. It is important to establish methods for estimating these parameters in order to develop correction methods for atmospheric effects. Such estimations can be based on climatological data, which are not available yet, correlations between the optical parameters and meteorological data, and the same satellite measurements of radiances that are used for estimating surface properties. Knowledge about the atmospheric parameters important for remote sensing is being enlarged with current measurements of them.

Fraser, R. S.↗
NASA NTRS1985

Emission, absorption and group delay of microwaves in the atmosphere in relation to water vapour content over the Indian subcontinent

The advent of satellite communication for global coverage has apparently indicated a renewed interest in the studies of radio wave propagation through the atmosphere, in the VHF, UHF and microwave bands. The extensive measurements of atmosphere constituents, dynamics and radio meterological parameters during the Middle Atmosphere Program (MAP) have opened up further the possibilities of studying tropospheric radio wave propagation parameters, relevant to Earth/space link design. The three basic parameters of significance to radio propagation are thermal emission, absorption and group delay of the atmosphere, all of which are controlled largely by the water vapor content in the atmosphere, particular at microwave bands. As good emitters are also good absorbers, the atmospheric emission as well as the absorption attains a maximum at the frequency of 22.235 GHz, which is the peak of the water vapor line. The group delay is practically independent of frequency in the VHF, UHF and microwave bands. However, all three parameters exhibit a similar seasonal dependence originating presumably from the seasonal dependence of the water vapor content. Some of the interesting results obtained from analyses of radiosonde data over the Indian subcontinent collected by the India Meteorological Department is presented.

Sen, A. K.↗
NASA NTRS1985

The photochemistry of the early atmosphere

The composition of the earth's present atmosphere is described. The formation of the earth from the coalescence and accretion of the refractory elements of the solar nebula is examined. Two possible compositions of the prebiological paleoatmosphere, which are a reducing atmosphere of CH4, NH3, and H2 or a mildly reducing atmosphere of H2O, CO2, and N2, and their photochemistry are analyzed. General photochemical and chemical processes are reviewed. The use of the coupled continuity-transport equation to calculate the vertical distribution of each species is discussed. A study of the photochemical process of CH4 and NH3 reveals that the reducing atmosphere could not possibly exist. An analysis of the photochemistry and chemistry of the H2O, CO2, and N2 atmosphere reveals that the photodissociation of H2O and CO2 results in a prebiotic source of O2, H2CO, and HCN, which are the components for the evolution of photosynthetic organisms and a strongly oxidizing atmosphere. The reactions which produce O2 and H2CO from H2O and CO2, and the relation between H2O and CO2 concentrations and O2 levels are investigated. The formation of O3 photochemically from O2 is explained.

Levine, J. S.↗
NASA NTRS1985

Photochemical consequences of enhanced CO2 levels in earth's early atmosphere

Greatly enhanced atmospheric CO2 concentrations are the most likely mechanism for offsetting the effects of reduced solar luminosity early in the earth's history. CO2 levels of 80 to 600 times the present value could have maintained a mean surface temperature of 0 C to 15 C, given a 25 percent decrease in solar output. Such high CO2 levels are at least qualitatively consistent with the present understanding of the carbonate-silicate geochemical cycle. The presence of large amounts of CO2 has important implications for the composition of the earth's prebiotic atmosphere. The hydrogen budget of a high-CO2 primitive atmosphere would have been strongly influenced by rainout of H2O2 and H2CO. The reaction of H2O2 with dissolved ferrous iron in the early oceans could have been a major sink for atmospheric oxygen. The requirement that this loss of oxygen be balanced by a corresponding loss of hydrogen (by escape to space and rainout of H2CO) implies that the atmospheric H2 mixing ratio was greater than 2 x 10 to the -5th and the ground level O2 mixing ratio was below 10 to the -12th, even if other surface sources of H2 were small. These results are only weakly dependent on changes in solar UV flux, rainout rates, and vertical mixing rates in the primitive atmosphere.

Kasting, J. F.↗
NASA NTRS1986

Stable carbon isotope ratios in atmospheric methane and some of its sources

Ratios of C-13/C-12 have been measured in atmospheric methane and in methane collected from sites and biota that represent potentially large sources of atmospheric methane. These include temperate marshes (about -48 percent to about -54 percent), landfills (about -51 percent to about -55 percent), and the first reported values for any species of termite (-72.8 + or - 3.1 percent for Reticulitermes tibialis and -57.3 + or - 1.6 percent for Zootermopsis angusticollis). Numbers in parentheses are delta C-13 values with respect to PDB (Peedee belemnite) carbonate. Most methane sources reported thus far are depleted in C-13 with respect to atmospheric methane (-47.0 + or - 0.3 percent). Individual sources of methane should have C-13/C-12 ratios characteristic of mechanisms of CH4 formation and consumption prior to release to the atmosphere. The mass-weighted average isotopic composition of all sources should equal the mean C-13 of atmospheric methane, corrected for a kinetic isotope effect in the OH attack of CH4. Assuming the kinetic isotope effect to be small (about -3.0 percent correction to -47.0), as in the literature, the new values given here for termite methane do not help to explain the apparent discrepancy between C-13/C-12 ratios of the known CH4 sources and that of atmospheric CH4.

Tyler, Stanley C.↗
NASA NTRS1986

The early atmosphere - A new picture

Over the last few years, discoveries in astronomy, geochemistry, and atmospheric chemistry have resulted in a new picture of how our planet and its atmosphere formed. The traditional view held that the early atmosphere was composed of methane, ammonia, and molecular hydrogen, but the actual composition may have been nitrogen, carbon dioxide, and water vapor. The history leading to the present understanding is discussed and topics covered include: chemical evolution, origin of the atmosphere, atmospheric evolution on earth, Venus, and Mars, and prebiological atmospheric oxygen and the early sun.

Levine, Joel S.↗
NASA NTRS1986

Atmospheric science on the Galileo mission

The atmospheric science goals of the Galileo mission, and instruments of the probe and orbiter are described. The current data available, and the goals of the Galileo mission concerning the chemical composition of the Jovian atmosphere; the thermal structure of the atmosphere; the nature of cloud particles and cloud layering; the radiative energy balance; atmospheric dynamics; and the upper atmosphere are discussed. The objectives and operations of the atmospheric structure instrument, neutral mass spectrometer, helium abundance interferometer, nephelometer, net flux radiometer, lightning and radio emission detector, solid state imaging system, NIR mapping spectrometer, photopolarimeter radiometer, and UV spectrometer are examined.

Hunten, D. M.↗
NASA NTRS1987

Laboratory evaluation and application of microwave absorption properties under simulated conditions for planetary atmospheres

Radio absorptivity data for planetary atmospheres obtained from spacecraft radio occultation experiments and Earth-based radio astronomical observations can be used to infer abundances of microwave absorbing atmospheric constituents in those atmospheres, as long as reliable information regarding the microwave absorping properties of potential constituents is available. The use of theoretically derived microwave absorption properties for such atmospheric constituents, or laboratory measurements of such properties under environmental conditions which are significantly different than those of the planetary atmosphere being studied, often leads to significant misinterpretation of available opacity data. Laboratory measurement of the microwave properties of atmospheric gases under simulated conditions for the outer planets were conducted. Results of these measurements are discussed.

Steffes, Paul G.↗
NASA NTRS1988

Development of an engineering model atmosphere for Mars

An engineering model atmosphere for Mars is being developed with many of the same features and capabilities for the highly successful Global Reference Atmospheric Model (GRAM) program for Earth's atmosphere. As an initial approach, the model is being built around the Martian atmosphere model computer subroutine (ATMOS) of Culp and Stewart (1984). In a longer-term program of research, additional refinements and modifications will be included. ATMOS includes parameterizations to stimulate the effects of solar activity, seasonal variation, diurnal variation magnitude, dust storm effects, and effects due to the orbital position of Mars. One of the current shortcomings of ATMOS is the neglect of surface variation effects. The longer-term period of research and model building is to address some of these problem areas and provide further improvements in the model (including improved representation of near-surface variations, improved latitude-longitude gradient representation, effects of the large annual variation in surface pressure because of differential condensation/sublimation of the CO2 atmosphere in the polar caps, and effects of Martian atmospheric wave perturbations on the magnitude of the expected density perturbation.

Justus, C. G.↗
NASA NTRS1987

Neutral upper atmospheres of the outer planets

The major characteristics of the neutral upper atmospheres of outer planets are discussed, with special attention given to the Uranus upper atmosphere, probed by Voyager 2. The composition, thermal structure, photochemistry, and vertical mixing of the Uranus atmosphere are compared with the respective features of other outer planets. Unlike the atmospheres of Jupiter and Saturn, which reflect the solar ratios of the elements, the Uranus atmosphere was found to have only few constituents, including NH3, CH4, H2, He, C2H2, and C2H6. The eddy diffusion coefficient of Uranus, determined from occultation experiments, was found to be in the range 10,000-100,000 sq cm/sec, the lowest value amongst the major planets; this implies relatively sluggish vertical mixing. Another major difference from Saturn and Jupiter is in the fact that stable hydrocarbon products (C2H2 and C2H6) in the Uranus atmosphere begin to condense at around 5-10 mb level, resulting in the production of haze in the lower stratosphere.

Atreya, S. K.↗
NASA NTRS1988

Acute effects of a large bolide impact simulated by a global atmospheric circulation model

The goal is to use a global three-dimensional atmospheric circulation model developed for studies of atmospheric effects of nuclear war to examine the time evolution of atmospheric effects from a large bolide impact. The model allows for dust and NOx injection, atmospheric transport by winds, removal by precipitation, radiative transfer effects, stratospheric ozone chemistry, and nitric acid formation and deposition on a simulated Earth having realistic geography. Researchers assume a modest 2 km-diameter impactor of the type that could have formed the 32 km-diameter impact structure found near Manson, Iowa and dated at roughly 66 Ma. Such an impact would have created on the order of 5 x 10 to the 10th power metric tons of atmospheric dust (about 0.01 g cm(-2) if spread globally) and 1 x 10 to the 37th power molecules of NO, or two orders of magnitude more stratospheric NO than might be produced in a large nuclear war. Researchers ignore potential injections of CO2 and wildfire smoke, and assume the direct heating of the atmosphere by impact ejecta on a regional scale is not large compared to absorption of solar energy by dust. Researchers assume an impact site at 45 N in the interior of present day North America.

Thompson, Starley L.↗