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NASA NTRS1975

Gaseous exhaust emissions from a JT8D-109 turbofan engine at simulated cruise flight conditions

Gaseous emissions from a JT8D-109 turbofan engine were measured in an altitude facility at four simulated cruise flight conditions: Mach 0.8 at altitudes of 9.1, 10, 7, and 12.2 km and Mach 0.9 at 10.7 km. Engine inlet air temperature was held constant at 283 K for all tests. Emissions measurements were made at nominally 6 cm intervals across the horizontal diameter of the engine exhaust nozzle with a single-point traversing gas sample probe. Measured emissions of decreased with increasing altitude from an emission index of 10.4 to one of 8.3, while carbon monoxide increased with increasing altitude from an emission index of 1.6 to one of 4.4. Unburned hydrocarbon emissions were essentially negligible for all flight conditions. Since the engine inlet air temperatures were not correctly simulated, the NOx emission indices were corrected to true altitude conditions by using correlating parameters for changes in combustor inlet temperature, pressure, and temperature rise. The correction was small at the lowest altitude. At the 10.7 and 12.2 km, Mach 0.8 test conditions the correction decreased the measured values by 1 emission index.

Diehl, L. A.↗

NASA NTRS1976

Seyfert galaxies with strong Fe II emission

Measurements are reported for the spectral energy distributions of the Seyfert galaxies Zw 2130+09 and Zw 0051+12 as well as the quasar 3C 273 over the wavelength range from 3300 to 10,760 A. Absolute emission-line intensities are derived for numerous Fe II blends and the O I line at 8446 A. Several new Fe II emission features are identified, the absence of Fe III emission is noted, and interesting properties of the individual spectra are described. Constraints on the ionizing continuum and on the geometry and velocity field of the emission-line regions are discussed. The observations show that Seyfert galaxies with strong Fe II emission also have strong O I 8446-A emission and that a flat continuum in the near-UV appears to be common in such objects. Assuming photoionization, it is suggested that both the Fe II and the O I emission could result from continuum fluorescence in an outer, optically thick H I zone in an emission-line region about 1 pc in radius and consisting of many small high-velocity filaments.

Oke, J. B.↗

NASA NTRS1980

The effect of local parameters on gas turbine emissions

Gas turbine engine inlet parameters reflect changes in local atmospheric conditions. The pollutant emissions for the engine reflects these changes. In attempting to model the effect of the changing ambient conditions on the emissions it was found that these emissions exhibit an extreme sensitivity to some of the details of the combustion process such as the local fuel-air ratio and the size of the drops in the fuel spray. Fuel-air ratios have been mapped under nonburning conditions using a single JT8D-17 combustion can at simulated idle conditions, and significant variations in the local values have been found. Modelling of the combustor employs a combination of perfectly stirred and plug flow reactors including a finite rate vaporization treatment of the fuel spray. Results show that a small increase in the mean drop size can lead to a large increase in hydrocarbon emissions and decreasing the value of the CO-OH rate constant can lead to large increases in the carbon monoxide emissions. These emissions may also be affected by the spray characteristics with larger drops retarding the combustion process. Hydrocarbon, carbon monoxide, and oxides of nitrogen emissions calculated using the model accurately reflect measured emission variations caused by changing engine inlet conditions.

Kauffman, C. W.↗

NASA NTRS1983

Phenomenology of magnetospheric radio emissions

Jupiter has now been observed over 24 octaves of the radio spectrum, from about 0.01 MHz to 300,000 MHz. Its radio emissions fill the entire spectral region where interplanetary electromagnetic propagation is possible at wavelengths longer than infrared. Three distinct types of radiation are responsible for this radio spectrum. Thermal emission from the atmosphere accounts for virtually all the radiation at the high frequency end. Synchrotron emission from the trapped high-energy particle belt deep within the inner magnetosphere is the dominant spectral component from about 4000 to 40 MHz. The third class of radiation consists of several distinct components of sporadic low frequency emission below 40 MHz. The decimeter wavelength emission is considered, taking into account the discovery of synchrotron emission, radiation by high-energy electrons in a magnetic field, and the present status of Jovian synchrotron phenomenology. Attention is also given to the decameter and hectometer wavelength emission, and emissions at kilometric wavelengths.

Carr, T. D.↗

NASA NTRS1985

The relation between hard X-ray and transition-region line emission in solar flares

Observational evidence suggests that both the hard X-ray and ultraviolet emission from the impulsive phase of flares result from an electron beam. The results of model calculations that are consistent with this theory are presented. The impulsive phase is envisioned as occurring in many small magnetically confined loops, each of which maintains an electron beam for only a few seconds. This model successfully matches several observed aspects of the impulsive phase. The corona is heated to less than 2 million K, maximum enhanced emission occurs in lines formed near 100,000 K, and there is only slight enhancement between 100,000 and 2 million K. The slope of the observed relationship between hard X-ray and Ov 1371 A emission is also matched, but the relative emission is not. The calculations indicate that UV emission lines formed below a temperature of about 100,000 K will arise predominantly from the chromospheric region heated by the electron beam to transition region temperatures. Emission lines formed at higher temperatures will be produced in the transition region. This should be detectable in density-sensitive line ratios. To account successfully for the impulsive UV emission, the peak temperature in the impulsively heated loops must remain below about 2 million K. Thus the model implies that the impulsive heating takes place in different loops from the hotter gradual phase emission.

Mariska, J. T.↗

NASA NTRS1987

Emission line region kinematics in selected Seyfert galaxies

The kinematic state of the emission line regions of active galactic nuclei (AGN) is a fundamental problem which addresses the very nature of these objects. The currently popular model of the energy source of the latter is accretion onto the supermassive black hole which is believed to reside in the nuclear regions of galaxies. If this picture is correct then the emission line gas may be expected to be infalling, and may eventually provide the fuel to power them. It is very difficult to determine the kinematic state of the emission line gas because of the technical problems associated with their small apparent sizes, as seen from the earth. One can only observe the net emission from a large ensemble of clouds, so the emission lines are by necessity composite. Several very long exposures of NGC 1068, one of the very nearest Seyfert galaxies, were obtained. Because of its proximity, it is expected to have the best resolved emission line regions as seen from earth. The La emission line of neutral hydrogen will radiate preferentially in the direction of the central object because of the effects of emission line gas opacity on the transfer of radiation out of the clouds. By obtaining high dispersion observations of Doppler broadening of the line through the small entrance aperture of the IUE one can determine whether this material is in a state of outflow (expected if explosions power the central engine), inflow (expected for accretion onto a massive black hole), or rotation (expected for gas with significant angular momentum near the central regions of a galaxy).

Ferland, G. J.↗

NASA NTRS1987

Is optical Fe II emission related to the soft X-ray properties of quasars?

Radio-quiet quasars generally show broad, blended multiplets of Fe II emission in their optical and UV spectra. Radio-loud quasars also show UV Fe II emission, but their optical Fe II emission is generally weaker. No satisfactory theory connecting the generation of Fe II and radio emission has been found to explain this effect. A second, well-established distinction between the two clases of quasar is in their X-ray properties: radio-loud quasars are more X-ray luminous, and recent results have shown that they also have systematically flatter soft X-ray slopes. Here it is proposed that the second effect causes the first; i.e., that the primary factor controlling the optical Fe II emission is the soft X-ray spectrum. This proposition is supported by X-ray and optical data for nine quasars, which shows a correlation between the soft X-ray slope and the strength of the optical Fe II emission. One of these quasars (1803+676) is radio-quiet, and yet its optical spectrum shows no evidence for Fe II emission. This quasar is also unusual in that it has a flat X-ray spectrum. This further supports the proposal that the X-ray spectrum is important in determining the relative strengths of UV and optical Fe II emission.

Wilkes, Belinda J.↗

NASA NTRS1987

Ordinary mode radio emission from Uranus

On Jan. 24, 1986, during the inbound trajectory to Uranus, the planetary radio astronomy instrument on Voyager 2 detected left-hand-polarized emission for several hours at frequencies near 200 kHz. Unlike the dominant source observed on the nightside of the planet, only a single episode of this inbound emission was seen, and the emission was extremely weak. Generating less than 500 kW, it is probably the weakest freely propagating planetary radio emission thus far observed by Voyager. This weak emission is associated with a source region in the vicinity of the north (dayside) magnetic pole of Uranus, where magnetic-field lines point approximately in the direction of the spacecraft when the emission is observed. Therefore the wave normal angle relative to B is probably less than 90 deg in the generation region. It is concluded that direct wave generation in the magnetoionic ordinary mode is most likely. The source location for this emission is consistent with a region magnetically conjugate to the dominant nightside source, which is located in the vicinity of the south magnetic pole. The ordinary mode emission is discussed in the context of the electron-cyclotron maser mechanism.

Desch, M. D.↗

NASA NTRS1989

Secondary electron emission characteristics of untreated and ion-textured titanium

Experimentally determined values of true secondary electron emission and relative values of reflected primary electron yield are presented for untreated (simply machined) and ion-textured, high-purity titanium over ranges of primary electron beam energies and beam impingement angles. The purpose of the investigation was to explore the feasibility of using titanium as electrode material in the multistage depressed collectors (MDC's) used in microwave amplifier traveling wave tubes (TWT's) for space communications and aircraft applications. Because of its relatively low density and thermal expansion characteristics and relatively high strength, thermal emissivity, and melting temperature, titanium presents itself as a possible candidate for the MDC electrode application. A detailed description of the method of ion texturing the titanium is included. Although the ion-treated surface considered in this study is not presented as being optimum from the standpoint of secondary electron emission suppression, it nevertheless serves to demonstrate that the surface can be modified by this procedure to significantly reduce these emission characteristics relative to those of the untreated surface. Further studies can reasonably be expected to produce surfaces with even lower secondary emission characteristics. The titanium surface were tested at primary electron beam energies of 200 to 2000 eV and at direct (0 deg) to near-grazing (85 deg) beam impingement angles. True secondary electron emission and relative reflected primary electron yield characteristics of the surfaces were compared with each other and with textured titanium surface exhibited secondary electron emission characteristics sharply lower than those exhibited by untreated titanium or copper. Clearly, then, in consideration of the secondary electron emission suppression of ion-textured titanium along with its other favorable physical properties, it must be included as a potential candidate for use as MDC electrode material in some applications.

Curren, Arthur N.↗

NASA NTRS1992

The X-ray spectra of galaxies. II - Average spectral properties and emission mechanisms

The Imaging Proportional Counter data in the Einstein database is used to study the X-ray spectra of normal galaxies. The X-ray emission temperature of spirals is found to be higher on the average than that of ellipticals. This supports the idea that accreting binaries are a major source of X-rays in spirals, while a hot interstellar medium (ISM) is present in ellipticals. The X-ray spectra of Sa galaxies are intermediate between those of ellipticals and spirals, suggesting that these galaxies contain hot gaseous emission as well as emission from accreting binaries. In E and SO galaxies the emission temperature becomes higher with a decreasing X-ray to optical luminosity ratio, which suggests that the emission of X-ray faint early-type galaxies consists of a large evolved stellar component, while the gaseous emission becomes dominant in X-ray brighter galaxies. The group with the lowest X-ray to optical ratio does not follow this trend; in these galaxies a very soft X-ray component, amounting to about half the total X-ray emission, is found in addition to the hard X-ray component. Possible explanations are integrated emission of M stars and a relatively cool ISM. A very soft component is also found in several spiral galaxies. This may indicate that some spirals contain hot gaseous components similar to those seen in NGC 253 and M82.

Kim, D.-W.↗

NASA NTRS1992

Emissions of biogenic sulfur gases from Alaskan tundra

Fluxes of the biogenic sulfur gases carbonyl sulfide (COS), dimethyl sulfide (DMS), methyl mercaptan (MeSH), and carbon disulfide (CS2) were determined for several freshwater and coastal marine tundra habitats using a dynamic enclosure method and gas chromatography. In the freshwater tundra sites, highest emissions, with a mean of 6.0 nmol/m(sup -2)H(sup -1) (1.5-10) occurred in the water-saturated wet meadow areas inhabited by grasses, sedges, and Sphagnum mosses. In the drier upland tundra sites, highest fluxes occurred in areas inhabited by mixed vegetation and labrador tea at 3.0 nmol/m(sup -2)h(sup -1) (0-8.3) and lowest fluxes were from lichen-dominated areas at 0.9 nmol/m(sup -2)h(sup -1). Sulfur emissions from a lake surface were also low at 0.8 nmol/m(sup -2)h(sup -1). Of the compounds measured, DMS was the dominant gas emitted from all of these sites. Sulfure emissions from the marine sites were up to 20-fold greater than fluxes in the freshwater habitats and were also dominated by DMS. Emissions of DMS were highest from intertidal soils inhabited by Carex subspathacea (150-250 nmol/m(sup -2)h(sup -1)). This Carex sp. was grazed thoroughly by geese and DMS fluxes doubled when goose feces were left within the flux chamber. Emissions were much lower from other types of vegetation which were more spatially dominant. Sulfure emissions from tundra were among the lowest reported in the literature. When emission data were extrapolated to include all tundra globally, the global flux of biogenic sulfur from this biome is 2-3 x 10(exp 8) g/yr. This represents less than 0.001 percent of the estimated annual global flux (approximately 50 Tg) of biogenic sulfur and less than 0.01 percent of the estimated terrestrial flux. The low emissions are attributed to the low availability of sulfate, certain hydrological characteristics of tundra, and the tendency for tundra to accumulate organic matter.

Hines, Mark E.↗

NASA NTRS1992

An algorithm for the estimation of bounds on the emissivity and temperatures from thermal multispectral airborne remotely sensed data

The effective flux incident upon the detectors of a thermal sensor, after it has been corrected for atmospheric effects, is a function of a non-linear combination of the emissivity of the target for that channel and the temperature of the target. The sensor system cannot separate the contribution from the emissivity and the temperature that constitute the flux value. A method that estimates the bounds on these temperatures and emissivities from thermal data is described. This method is then tested with remotely sensed data obtained from NASA's Thermal Infrared Multispectral Scanner (TIMS) - a 6 channel thermal sensor. Since this is an under-determined set of equations i.e. there are 7 unknowns (6 emissivities and 1 temperature) and 6 equations (corresponding to the 6 channel fluxes), there exist theoretically an infinite combination of values of emissivities and temperature that can satisfy these equations. Using some realistic bounds on the emissivities, bounds on the temperature are calculated. These bounds on the temperature are refined to estimate a tighter bound on the emissivity of the source. An error analysis is also carried out to quantitatively determine the extent of uncertainty introduced in the estimate of these parameters. This method is useful only when a realistic set of bounds can be obtained for the emissivities of the data. In the case of water the lower and upper bounds were set at 0.97 and 1.00 respectively. Five flights were flown in succession at altitudes of 2 km (low), 6 km (mid), 12 km (high), and then back again at 6 km and 2 km. The area selected with the Ross Barnett reservoir near Jackson, Mississippi. The mission was flown during the predawn hours of 1 Feb. 1992. Radiosonde data was collected for that duration to profile the characteristics of the atmosphere. Ground truth temperatures using thermometers and radiometers were also obtained over an area of the reservoir. The results of two independent runs of the radiometer data averaged 7.03 plus or minus .70 for the first run and 7.31 plus or minus .88 for the second run. The results of the algorithm yield a temperature of 7.68 for the low altitude data to 8.73 for the high altitude data.

Jaggi, S.↗

NASA NTRS1993

Polarimetric thermal emission from rough surfaces

Recent theoretical works have suggested the potential of passive polarimetry in the remote sensing of geophysical media. It was shown that the third Stokes parameter U of the thermal emission may become larger for azimuthally asymmetric fields of observation. In order to investigate the potential applicability of passive polarimetry to the remote sensing of ocean surface, measurements of the polarimetric thermal emission from a sinusoidal water surface and a numerical study of the polarimetric thermal emission from randomly rough ocean surfaces were performed. Measurements of sinusoidal water surface thermal emission were performed using a sinusoidal water surface which was created by placing a thin sheet of fiberglass with a sinusoidal profile in two dimensions extended infinitely in the third dimension onto a water surface. The theory of thermal emission from a 'two-layer' periodic surface is derived and the exact solution is performed using both the extended boundary condition method (EBC) and the method of moments (MOM). The theoretical predictions are found to be in good agreement with the experimental results once the effects of the radiometer antenna pattern are included and the contribution of background noise to the measurements is modeled. The experimental results show that the U parameter indicates the direction of periodicity of the water surface and can approach values of up to 30 K for the surface observed. Next, a numerical study of polarimetric thermal emission from randomly rough surfaces was performed. A Monte Carlo technique utilizing an exact method for calculating thermal emission was chosen for the study to avoid any of the limitations of the commonly used approximate methods in rough surface scattering. In this Monte Carlo technique, a set of finite rough surface profiles in two dimensions with desired statistics was generated and extended periodically. The polarimetric thermal emission from each surface of the set was then calculated using both the EBC and the MOM and the results were averaged. The surface statistics chosen were intended to model a wind perturbed ocean surface in the X to Ku band microwave region. The results indicate that the U parameter is sensitive to the azimuthal angle between the surface periodicity and the looking angle and to the rms height of the surface, and that the U parameter is fairly insensitive to variations in polar angle, permittivity, surface power law spectrum, and surface spectrum high frequency cutoff. These properties give further strength to the idea of using the U parameter to detect wind direction over the ocean.

Johnson, J. T.↗

NASA NTRS1993

Thermal infrared emission spectroscopy of natural surfaces: Application to desert varnish coatings on rocks

Thermal infrared spectroscopy has become an increasingly important tool for remote compositional analysis and geologic mapping. Most published laboratory measurements have been obtained in bidirectional reflection or transmission, whereas remotely sensed thermal infrared data are obtained by measuring the emitted energy. Section 2 of this paper describes a laboratory technique for determining calibrated emissivities of natural surfaces. Equations are developed to account for the energy reflected from the environment and to determine directly the sample temperature from measurements of hot and cold blackbody targets. Two methods for determining emissivity are developed: one in which only a hot sample measurement is made and the reflected background energy is removed by modeling, and a second in which the sample is cooled and the reflected energy is measured directly. Relative emissivity can be obtained to approximately 1% and absolute emissivities can be obtained to 2-15%, depending on the validity of the assumption that the emissivity of the sample is unity at some wavelength. The emission data agree well within the hemispherically integrated reflection data but point out probelms associated with bidirectional reflectance measurements. Section 3 applies emissivity measurements to the study of layered surfaces consisting of desert varnish coatings on granite and granodiorite rock suites. Two linear models are developed: the first assumes linear mixing of independent emission from the substrate and varnish (checkerboard model); the second models tansmission through an absorbing/emitting medium. Regardless of whether the varnish is or is not relatively transparant and strongly absorptive, the spectral effect of varnish increases linearly with varnish thickness, indicating that thick patches of varnish dominate the spectral properties. As a result, medium varnish thickness can be determined from spectral measurements. In addition, the composition of a substrate can be estimated through varnish layers up to 40-50 micrometers in median thickness, and the composition of the varnish material can be determined if the substrate material is known. The varnishes studied are composed primarily of clay materials, consistent with previous studies of varnish composition.

Christensen, Philip R.↗

NASA NTRS1994

The emission-line properties of the QSO population at z approximately 2

We compare the ultraviolet emission-line properties of the three subclasses of the QSO population (radio quiet, flat radio spectrum radio loud, steep radio spectrum radio loud) during the 'QSO epoch' at z approximately 2. Our total sample consists of 79 objects that are well matched in luminosity and redshift, which should allow unbiased comparison of their spectral properties. We confirm recent results that radio-loud objects have, on average, narrower and stronger C IV lambda 1549 and C III) lambda 1909 emission lines than radio-quiet objects. This is likely the effect of larger average intermediate-line and/or narrow-line regions in radio loud objects, including a relative excess of emission on very extended (approximately 100 kpc) scales. We additionally find that radio-loud objects show a significantly wider range in the asymmetry of the C IV lambda 1549 profile than radio-quiet objects, with cases of both redward and blueward asymmetry. By contrast, radio-quiet objects almost exclusively show blueward asymmetry in this line, and cases of strong redward asymmetry appear to be limited to steep-spectrum objects. Statistically, there is a closer correspondence between the emission-line properties of radio-quiet and flat-spectrum objects than between either of these subclasses and steep-spectrum objects, whose mean emission-line properties differ strongly from those of the radio-quiet sample. This result is similar to that found for the properties of the optical emission lines in low-redshift objects and is not easily understood under the proposed unified models of the flat- and steep-spectrum sources. We also find that 20%-30% of radio-loud objects show narrow (approximately 1000 km/s) emission in He II lambda 1640. No cases of such emission are found among radio-quiet objects. There is evidence that this spectral feature arises in extended ionized halos, which may thus be associated with the objects' radio ejecta, cluster cooling flows, or a combination of both.

Corbin, Michael R.↗

NASA NTRS1995

Tidal influence on O(1S) airglow emission rate distributions at the geographic equator as observed by WINDII

WINDII, the Wind Imaging Interferometer on the Upper Atmosphere Research Satellite, observes winds, temperatures and emission rates in the upper mesosphere and thermosphere. In this paper we report on nighttime observations of the vertical distribution of the O(1S) 557.7 nm emission near the geographic equator for March/April, 1993. The airglow volume emission rate distribution is found to be strongly dependent on local time. Beginning at dusk, an intense airglow emission layer descends from a mean altitude of 95 km, reaching 89 km by midnight after which the emission rapidly decays. Shortly after midnight it reappears weakly at a higher altitude and remains at this level as the emission rate gradually increases towards dawn. This strong local time dependence leads us to conclude that the effect is tidally driven. Comparison with the Forbes (1982a,b) model suggest that total density perturbations and changes in the atomic oxygen mixing ratio may the cause of the changes in emission rate distribution between dusk and midnight. The reappearance of the emission after midnight may be caused by downward winds bringing oxygen-rich air from above.

Shephere, G. G.↗

NASA NTRS1996

Infrared Spectroscopy of Pa-beta and [Fe II] Emission in NGC 4151

We present spatially resolved 1.24-1.30 micron spectroscopy with a resolution of 240 km/s of the Seyfert 1.5 galaxy NGC 4151. Broad Pa-beta, narrow Pa-beta, and narrow [Fe II] (lambda = 1.2567 micron) emission lines are identified in the spectrum. Additionally, a spatially unresolved narrow component probably due to [S ix] (lambda = 1.25235 micron) is observed on the nucleus. The narrow Pa-beta and [Fe II] lines are observed to be extended over a scale of 5 sec. The spatial variation of the velocity centers of the Pa-beta and [Fe II] lines show remarkable similarity, and additionally show similarities to the velocity structure previously observed in ground based spectroscopy of [O III] emission in NGC 4151. This leads to the conclusion that the [Fe II] emission arises in clouds in the Seyfert narrow line region that are physically correlated with those narrow line clouds responsible for the optical emission. The [Fe II] emission line, however, is significantly wider than the Pa-beta emission line along the full spatial extent of the observed emission. This result suggests that despite the correlation between the bulk kinematics of Pa-beta and [Fe II], there is an additional process, perhaps fast shocks from a wind in the Seyfert nucleus, contributing to the [Fe II] emission.

Knop, R. A.↗

NASA NTRS1959

Measurements of Total Hemispherical Emissivity of Several Stably Oxidized Metals and Some Refractory Oxide Coatings

A description of the apparatus and methods used for obtaining total hemispherical emissivity is presented, and data for several stably oxidized metals are included. The metals which were tested included type 347 stainless steel, tungsten, and Haynes alloys B, C, X, and 25. No values of emissivity were obtained for tungsten or Haynes alloy B because of the nature of the oxides produced. The refractory oxide coatings tested were flame-sprayed alumina and zirconia. The results of the investigation indicate that strongly adherent, oxidized surfaces of a high stable emissivity can be produced on type 347 stainless steel for which the total hemispherical emissivity varied from 0.87 to 0.91 for temperatures from 600 F to 2,000 F. For this same temperature range, the Haynes alloys tested showed values of total hemispherical emissivity from 0.90 to 0.96 for alloy C, from 0.85 to 0.88 for alloy X, and from 0.85 to 0.89 for alloy 25. Haynes alloy B and tungsten formed nonadherent oxides at elevated temperatures and, therefore, stable emissivities were not obtained. The results obtained for the flame-sprayed ceramics (alumina and zirconia) showed considerably higher values of total emissivity than those measured for coatings applied by other methods. Emissivity values ranging from 0.69 to 0.44 for aluminum oxide and from 0.62 to 0.44 for zirconium oxide were measured for temperatures from 800 F to 2,000 F.

Wade, William R.↗