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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Evaluation and analysis of Seasat-A scanning multichannel Microwave Radiometer (SMMR) Antenna Pattern Correction (APC) algorithm

The brightness temperature data produced by the SMMR final Antenna Pattern Correction (APC) algorithm is discussed. The algorithm consisted of: (1) a direct comparison of the outputs of the final and interim APC algorithms; and (2) an analysis of a possible relationship between observed cross track gradients in the interim brightness temperatures and the asymmetry in the antenna temperature data. Results indicate a bias between the brightness temperature produced by the final and interim APC algorithm.

Kitzis, J. L.↗
NASA NTRS1979

Flow visualization studies of a general research fighter model employing a strake-wing concept at subsonic speeds

A systematic wind tunnel study was conducted in the Langley high-speed 7 by 10 foot tunnel to document, by oil-flow photographs, the surface flow patterns for configurations incorporating strake-wing geometries indicative of current and proposed maneuvering aircraft. The configurations employed combinations of strakes with reflexed planforms having exposed spans of 10 percent, 20 percent, and 30 percent of the reference wing span and wings with trapezoidal planforms having leading-edge sweep angles of approximately 30 deg, 44 deg, and 60 deg. Tests were conducted at Mach numbers of 0.3 and 0.5 and at angles of attack ranging from approximately 5 deg to 30 deg in 5 deg increments at 0 deg sideslip. The configurations incorporating the strake-wing geometries exhibited more organized flow patterns with smaller asymmetries to higher angles of attack than the corresponding configurations incorporating the wing-alone geometries did.

Luckring, J. M.↗
NASA NTRS1978

Radiative transfer in spherical shell atmospheres. II - Asymmetric phase functions

This paper investigates the effects of sphericity on the radiation reflected from a planet with a homogeneous conservative-scattering atmosphere of optical thicknesses of 0.25 and 1.0. A Henyey-Greenstein phase function with asymmetry factors of 0.5 and 0.7 was considered. Significant differences were found when these results were compared with the plane-parallel calculations. Also, large violations of the reciprocity theorem, which is only true for plane-parallel calculations, were noted. Results are presented for the radiance versus height distributions as a function of planetary phase angle. These results will be useful to researchers in the field of remote sensing and planetary spectroscopy.

Kattawar, G. W.↗
NASA NTRS1977

Pioneer-Venus large probe infrared radiometer /LIR/ optical system

The LIR (large probe infrared radiometer) instrument has been developed for the NASA Ames Research Center for use in the 1978 Venus Atmospheric Probe Mission. The mission objectives are to determine the nature and composition of the clouds, the composition and structure of the atmosphere, and the atmospheric circulation pattern of the planet Venus. The LIR is a six-channel (3-50 micron) internally calibrated radiometer which measures the radiance difference at plus or minus 45 deg to the horizontal as viewed through a single diamond window in the spacecraft. The LIR optical system consists of a unique arrangement of hollow light pipes which optically couple a six element detector/filter array to the spacecraft window while mechanically and thermally isolating the array from the window's harsh thermal environment. A single rotating section with a 45 deg bend and containing a collimator alternately views up and down through director/extender pipes located adjacent to the diamond window. Light is transferred from the rotating section to a fixed section containing a diamond diffuser to scramble the light. This minimizes asymmetries and improves channel field of view overlap.

Brown, F. G.↗
NASA NTRS1978

Global exchange of water vapor on Mars

Observations of the global distribution and seasonal variation of the Martian atmospheric water vapor have been made from the Viking orbiters for a continuous period covering more than half of a Martian year. The seasonal dependence of the latitude distribution of the column abundance of vapor is consistent with a model in which the vapor is in equilibrium with the regolith at polar and middle latitudes. The results indicate the existence of a permanent reservoir of water ice buried at a depth of 10 cm to 1 meter at all latitudes poleward of 40 deg. The behavior of the vapor in the summer hemisphere suggests an annual net transport of the vapor phase from the southern to the northern hemisphere, with deposition of ice of thickness on the order of a few milligrams per sq cm at northern polar latitudes. The hemispheric asymmetry is the result of the propagation of global dust storms originating in the south.

Farmer, C. B.↗
NASA NTRS1978

Pictures of the Io sodium cloud

We obtained and processed 56 pictures of Io's sodium cloud on 15 nights during the 1976-1977 apparition of Jupiter. These show rapid changes in the appearance of the cloud, but may be consistent with a steady-state cloud whose appearance is controlled by the viewing geometry. The sodium is in a column extending forward from Io, with the axis pointing slightly inside the orbit. The size and shape of the cloud convey information on the anisotropy and velocity of emission and the lifetime of neutral sodium. We find some confirnation for Trafton's findings of north/south asymmetries related to the position of the magnetic field.

Murcray, F. J.↗
NASA NTRS1978

Phase coverage of Venus during the 1975 apparition

Day-night contrasts in the equatorial infrared (8- to 14-micrometers) flux from Venus were observed in digital images obtained during the 1975 apparition. A systematic increase in 8- to 14-micrometers flux associated with the emergence of the atmosphere from daylight into evening was observed and is shown to exhibit significant day-to-day variability. The data also show that the daytime side of the morning terminator is warmer than the dark side, but this night-day asymmetry is systematically smaller than the day-night brightening seen in the Venus evening.

Diner, D. J.↗
NASA NTRS1978

Discovery of polarized light scattered by dust around Alpha Orionis

Following the suggestion by Jura and Jacoby (1976), linearly polarized blue continuum starlight scattered by the dust shell around the M2 Iab star Alpha Orionis (Betelgeuse) has been discovered. The polarization has been traced in the NE, NW, SE, and SW directions and has positive (tangential) orientation. Some asymmetry of the optical depth in the shell exists 15 and 30 arcsec from the star. In the NE direction the polarization was measured as far as 90 arcsec (17,000 AU) from the star. The dependence of the average intensity of the scattered light from the nebula on angular distance from the star is more consistent with an inverse-square density law than with inverse 1.5 or inverse-cube laws. Assuming that the density is proportional to the inverse square of distance from the star, the scattering optical depth in blue light along a radius of 0.03 arcsec is no more than 0.15 + or - 0.05. Future observations of the wavelength dependence of polarization will allow a determination of grain size.

Mcmillan, R. S.↗
NASA NTRS1978

Effect of tropospheric aerosols upon atmospheric infrared cooling rates

The effect of tropospheric aerosols on atmospheric infrared cooling rates is investigated by the use of recent models of infrared gaseous absorption. A radiative model of the atmosphere that incorporates dust as an absorber and scatterer of infrared radiation is constructed by employing the exponential kernel approximation to the radiative transfer equation. Scattering effects are represented in terms of a single scattering albedo and an asymmetry factor. The model is applied to estimate the effect of an aerosol layer made of spherical quartz particles on the infrared cooling rate. Calculations performed for a reference wavelength of 0.55 microns show an increased greenhouse effect, where the net upward flux at the surface is reduced by 10% owing to the strongly enhanced downward emission. There is a substantial increase in the cooling rate near the surface, but the mean cooling rate throughout the lower troposphere was only 10%.

Harshvardhan, MR.↗
NASA NTRS1979

The magnetic anomaly model of the Jovian magnetosphere - Predictions for Voyager

The magnetic anomaly model, in which the anomalously weak magnetic field region in the northern hemisphere of Jupiter influences the outer Jovian magnetosphere by one or more plasma interaction processes, has been put forth to account for the various observed Jovian magnetospheric phenomena that show evidence of Jovian longitudinal asymmetry or planetary spin periodicity. From this model, normalized by empirical fitting to Pioneer 10 and 11 flyby data and to ground-based radio data, a series of predictions are made that are subject to test by the forthcoming flybys of Jupiter by Voyagers 1 and 2. These predictions cover: (1) the longitude range and time intervals of enhanced interaction between Io (and possibly Europa) and Jupiter's ionosphere, (2) plasma, energetic particle, and magnetic field periodicities in the outer magnetosphere, and (3) the sub-spacecraft System III longitude and the time, modulo 10 hours, of the first and subsequent magnetopause crossings.

Dessler, A. J.↗
NASA NTRS1979

Signatures of solar wind latitudinal structure in interplanetary Lyman-alpha emissions - Mariner 10 observations

A detailed analysis is conducted which shows that signatures in the interplanetary Lyman-alpha emissions observed in three different data sets from Mariner 10 (corresponding to different locations of the spacecraft) provide firm evidence that the intensity departures are correlated with a decrease in solar wind flux with increasing latitude. It is suggested that observations of the interplanetary emission can be used to monitor average solar wind activity at high latitudes. The asymmetry in the solar radiation field as a source of observed departures in L-alpha data is considered and attention is given to the interstellar hydrogen and helium density.

Kumar, S.↗
NASA NTRS1979

Detection of soft X-ray emission from SMC X-1

The observation of 0.25-keV X-rays from SMC X-1 by a soft X-ray experiment aboard OSO 8 is reported. The variable soft X-ray source observed is identified with the hard X-ray source SMC X-1 on the basis of a rather abrupt ending to the emission (fall time about 2.5 hr) at the time SMC X-1 was expected to enter eclipse. A source luminosity of about 5 x 10 to the 38th erg/s in the 0.18-0.28-keV range is derived by assuming a distance of 68 kpc and correcting for attenuation by 3.4 x 10 to the 20th H atoms per sq cm of intervening galactic gas; this luminosity is shown to be about a factor of 40 greater than the observed coincident luminosity in the 0.8-3-keV band. The soft X-ray intensity upon emergence from eclipse is found to be reduced by a factor of at least 20 from the peak intensity prior to eclipse. It is suggested that this asymmetry may reflect a geometry in which the soft X-ray source trails the compact star as in an accretion-stream model.

Bunner, A. N.↗
NASA NTRS1979

Improvement of scanning radiometer performance by digital reference averaging

Most radiometers utilize a calibration technique in which measurements of a known reference are subtracted from measurements of an unknown source so that common-mode bias errors are cancelled. When a radiometer is scanned over a varying scene, it produces a sequence of outputs, each being proportional to the difference between the reference and the corresponding input. A reference averaging technique is presented that employs a simple digital algorithm which exploits the asymmetry between the time-variable scene inputs and the nominally constant reference input by averaging many reference measurements to decrease the statistical uncertainty in the reference value. This algorithm is, therefore, optimized by an asymmetric chopping sequence in which the scene is viewed for more than one-half of the duty cycle (unlike the analog Dicke technique). Reference averaging algorithms are well within the capabilities of small microprocessors. Although this paper develops the technique for microwave radiometry, it may be beneficial for any system which measures a large number of unknowns relative to a known reference in the presence of slowly varying common-mode errors.

Bremer, J. C.↗
NASA NTRS1979

Numerical results for the thermal scattering functions

A recent formulation in radiative transfer defined the thermal scattering functions that characterize radiative transfer from a general plane-parallel finite medium driven solely by an internal distribution of thermal sources. Exiting diffuse intensities are expressed as space convolutions of the thermal scattering functions with any thermal source distribution. A parametric study is presented to obtain the basic structure of these scattering functions. The independent variables of these azimuthally independent functions are the direction cosine and source location, while the parameters are the single-scattering albedo, total optical depth, and the asymmetry factor in the Henyey-Greenstein phase function. The basic functional trends are discussed by using various parametric plots, and selected results are given to allow numerical checks. The computational method is invariant imbedding.

Cogley, A. C.↗
NASA NTRS1978

Physical conditions in the emission-line regions of BL Lac objects and QSOs

BL Lac objects have weak emission lines because of the absence of even a small amount (about 1 solar mass) of gas at high densities. The large forbidden N II/H-alpha intensity ratio of BL Lac indicates that a substantial mass (at least about 1000 solar masses) of gas is present, with a high nitrogen abundance. The broad line profiles of QSOs and Sy 1 galaxies are difficult to understand in terms of infall or orbital motion, but are consistent with outflow possibly resulting from radiation pressure. The asymmetries of the line profiles are a natural consequence of self-absorption in the outflowing clouds. Over a wide range in luminosity, the radius of the broad-line region adjusts itself so that the incident flux is the same; the regulation mechanism may involve the evaporation of refractory grains. The ratio of radiation flux to gas density also is constant over a wide range of luminosity, and this can be understood in terms of radiation pressure. The absence of strong emission lines in BL Lac objects may be related to the geometry of an accretion flow that fuels the luminosity.

Shields, G. A.↗
NASA NTRS1979

Dust release and mantle development in comets

A model of dust release and dust mantle development by cometary nuclei is developed to explain the brightness asymmetry observed in comets before and after perihelion. Assuming that the cometary nucleus consists of a uniform mixture of dust and volatile ices and taking into account the differential mass spectrum of the dust and the effect of nuclear gravity, it is shown that the factor which determines whether a comet will be brighter before or after perihelion is the mass ratio of dust to volatiles in the nucleus. If this ratio is greater than about two, the comet will be brighter on the inward path and not lose its mantle near perihelion. Applying the model to comet Halley (dust to volatiles ratio presumed to be less than two), it is predicted that the comet remains without a mantle until it reaches a heliocentric distance of 2.035 AU after perihelion and loses its mantle suddenly at a distance of about 1.45 AU on the inward path, causing it to be brighter after perihelion. Predictions of monochromatic brightness are found to be in fair agreement with total observed brightnesses.

Brin, G. D.↗
NASA NTRS1979

A Copernicus survey of Mg II emission in late-type stars

The behavior of Mg II emission in late-type stars is examined using scan data obtained with the Copernicus satellite. The luminosity in the Mg II k emission line was found to be closely related to stellar absolute magnitude, leading to the suggestion that such correlation may be very useful for future UV observations. The stellar surface flux in the k line was observed to be roughly constant or to decrease slowly with later spectral type, a finding which is then used to show that the pressure at the top of the chromosphere decreases with later spectral type, in agreement with the conclusions by McClintock et al. (1975). An asymmetry in the Mg II k line was noticed to be present in the available data for the stars later than K2-K5.

Weiler, E. J.↗
NASA NTRS1979

The magnetic field of Jupiter - A comparison of radio astronomy and spacecraft observations

The inner magnetic field of Jupiter is characterized on the basis of Pioneer 10 and 11 measurements and earth-based decimetric radio observations. The dipole parameters derived from the two data sets are in good agreement. Problems in reconciling asymmetries observed in the earth-based data and the spacecraft data are discussed. Models of synchrotron emission from arbitrary magnetic field configurations and high-resolution maps of the Jovian radiation belts in all polarizations are needed to further understanding of Jupiter's magnetic field

Smith, E. J.↗