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At least 451 records · Page 25

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NASA NTRS1981

Correlation function studies for snow and ice

The random medium model is used to characterize snow and ice fields in the interpretation of active and passive microwave remote sensing data. A correlation function is used to describe the random permittivity fluctuations with the associated mean and variance and correlation lengths; and several samples are investigated to determine typical correlation functions for snow and ice. It is shown that correlation functions are extracted directly from appropriate ground truth data, and an exponential correlation function is observed for snow and ice with lengths corresponding to the actual size of ice particles or air bubbles. Thus, given that a medium has spatially stationary statistics and a small medium, the random medium model can interpret remote sensing data where theoretical parameters correspond to actual physical parameters of the terrain.

Vallese, F.↗

NASA NTRS1979

Low-speed aerodynamic performance of a high-aspect-ratio supercritical-wing transport model equipped with full-span slat and part-span double-slotted flaps

An investigation was conducted in the Langley V/STOL tunnel to determine the static longitudinal and lateral-directional aerodynamic characteristics of an advanced high-aspect-ratio supercritical-wing transport model equipped with a full-span leading-edge slat and part-span double-slotted trailing-edge flaps. This wide-body transport model was also equipped with spoiler and aileron control surfaces, flow-through nacelles, landing gear, movable horizontal tails, and interchangeable wing tips with aspect ratios of 10 and 12. The model was tested with leading-edge slat and trailing-edge flap combinations representative of cruise, climb, takeoff, and landing wing configurations. The tests were conducted at free-stream conditions corresponding to Reynolds numbers (based on mean geometric chord) of 0.97 to 1.63 x 10 to the 6th power and corresponding Mach numbers of 0.12 to 0.20, through an angle-of-attack range of -2 deg to 24 deg and a sideslip-angle range of -10 deg to 5 deg.

Morgan, H. L., Jr.↗

NASA NTRS1981

Description of the NRL isothermal haze chamber

In the IHC the critical supersaturation is inferred from the measurement of the size of particles which have grown to their equilibrium size at exactly 100 percent RH. The largest size channel corresponds to a critical supersaturation of 0.014 percent. The growth time required for particles of this size to reach their equilibrium size exceeds the 110 second residence time in the IHC. Since the supersaturation spectrum is always very steep in this region, the contribution of these larger particles which have not yet attained their equilibrium size to smaller size channels is negligible. However, failure of these particles to reach their equilibrium size could result in a significant lowering of the count in the size channel corresponding to the smaller critical supersaturation.

Hoppel, W. A.↗

NASA NTRS1981

The variability of the solar output

A review of solar constant determinations and measurements of its spectral distribution is presented. For the period from 1966 to 1980 a mean value of 1367 Wm-2 was determined. Within the corresponding uncertainty, no significant change of both the integral value and the spectral distribution can be detected. However, short term solar variations and their spectral dependence were deduced from measurements during four hours on June 20, 1980 from 34 km altitude with amplitudes of + or - 500 ppm at 368 nm, of 200 ppm at 500 nm and + or - 150 ppm at 778 nm. Comparison with simultaneous total irradiance data of the Solar Maximum Mission (SMM) shows a high correlation which indicates the solar origin. The power spectrum shows a weak peak at about 3.2 mHz, which corresponds to the frequency of the 5 minutes solar oscillation.

Froehlich, C.↗

NASA NTRS1981

As-built design specification for the CLASFYG program

This program produces a file with a Universal-formatted header and data records in a nonstandard format. Trajectory coefficients are calculated from 5 to 8 acquisitions of radiance values in the training field corresponding to an agricultural product. These coefficients are then used to calculate a time of emergence and corresponding trajectory coefficients for each pixel in the test field. The time of emergence, two of the coefficients, and the sigma value for each pixel are written to the file.

Horton, C. L.↗

NASA NTRS1981

High-latitude stratospheric aerosols measured by the SAM II satellite system in 1978 and 1979

Results of the first year of data collection by the SAM (Stratospheric Aerosol Measurement) II satellite system are presented. Almost 10,000 profiles of stratospheric aerosol extinction in the Arctic and Antarctic regions are used to construct plots of weekly averaged aerosol extinction versus altitude and time and stratospheric optical depth versus time. Corresponding temperature fields are presented. These data show striking similarities in the aerosol behavior for corresponding seasons. Wintertime polar stratospheric clouds that are strongly correlated with temperature are documented. They are much more prevalent in the Antarctic stratosphere during the cold austral winter and increase the stratospheric optical depths by as much as an order of magnitude for a period of about 2 months. These clouds might represent a sink for stratospheric water vapor and must be considered in the radiative budget for this region and time.

Mccormick, M. P.↗

NASA NTRS1981

Inversion technique for IR heterodyne sounding of stratospheric constituents from space platforms

The techniques which have been employed for inversion of IR heterodyne measurements for remote sounding of stratospheric trace constituents usually rely on either geometric effects based on limb-scan observations (i.e., onion peel techniques) or spectral effects by using weighting functions corresponding to different frequencies of an IR spectral line. An experimental approach and inversion technique are discussed which optimize the retrieval of concentration profiles by combining the geometric and the spectral effects in an IR heterodyne receiver. The results of inversions of some synthetic CIO spectral lines corresponding to solar occultation limb scans of the stratosphere are presented, indicating considerable improvement in the accuracy of the retrieved profiles. The effects of noise on the accuracy of retrievals are discussed for realistic situations.

Abbas, M. M.↗

NASA NTRS1981

The solar modulation of galactic cosmic rays in the outer heliosphere

The intensity changes of galactic cosmic rays associated with the enhanced solar activity during the onset of cycle 21 were observed by Pioneer 10 and Helios 1 and 2, over an extended range of energy and heliocentric distance that provides new insight into the relative importance of the various processes involved in the long-term modulation. A close correspondence is found between changes at 1 AU and those at 23 AU, for hydrogen and helium in the range of 100-200 MeV per nucleon. The time delay observed corresponds to an outward propagation velocity of some 550 km/sec, suggesting that the recently discovered, moderately long-lived, radially propagating shock waves in the outer heliosphere may play a key role in the long-term modulation.

Mcdonald, F. B.↗

NASA NTRS1980

K/Ar dating of lunar soils. IV - Orange glass from 74220 and agglutinates from 14259 and 14163

Total fusion Ar-40 - A-39 analyses of orange glass from lunar soil 74220 combined with the sums of earlier stepwise heating data by other workers have yielded a precise K/Ar isochron with a slope corresponding to an age of 3.66 + or - 0.03 G.y. for the orange glass. The result is in marginal agreement with Huneke's (1978) age of 3.60 + or - 0.04 G.y. for 74220 glass. The Ar systematics in the agglutinates from 14259 and 14163 are dominated by volume correlated argon. Step-wise heating analyses yield data which define experimentally reproducible linear arrays in Ar-40/Ar-36 vs. K-40/Ar-36 diagrams. The slopes of these arrays correspond formally to very old ages, but it is not clear, however, that such ages have any physical significance.

Alexander, E. C., Jr.↗

NASA NTRS1982

Time variability and structure of quiet sun sources at 6 cm wavelength

Results are presented of a detailed study of quiet sun emitting regions at 6 cm and their correspondence with regions observed at optical wavelengths. The Westerbork Synthesis Radio Telescope was used to obtain a 12-hr synthesis map of a quiet sun region with a resolution of 6 arcsec. Comparison of this map with a Ca(+) K filtergram indicates the features on the 6-cm map to correspond to Ca(+) K chromospheric networks and cells. In addition, about 72% of the magnetic field enhancements observed on photospheric magnetograms coincides with 6-cm emissive regions. Intercomparison of the 12-hr synthesis map, a 4-hr synthesis map and 6-cm fan beam scans along with the Ca(+) K and magnetogram results reveals all of the time-varying 6-cm elements to be located on Ca(+) K networks, and about 40% of them to be coincident with magnetogram enhancements. Lifetimes of the time-varying sources vary from a few minutes to several tens of minutes, and intensity varies by factors of 2 to 7.

Erskine, F. T.↗

NASA NTRS1982

Plasma wave levels and IMF orientations preceding observations of interplanetary shocks by ISEE-3

Some interplanetary shocks detected by ISEE-3 are preceded by many hours of strongly enhanced plasma wave noise at a few kHz, while others have essentially no wave precursors above background. It has been shown that these extremes correspond to quasi-parallel and quasi-perpendicular shocks, respectively, based on the instantaneous orientation angle of the interplanetary magnetic field (IMF) to the shock normal at the time the shocks cross the spacecraft. It is shown that precursor wave noise level is correlated with field orientation and an extrapolated instantaneous orientation angle throughout the preshock observation interval for two contrasting active and quiet cases, and that intermediate, variable noise levels correspond to intermediate, variable IMF orientations. It is inferred that foreshocks are an intrinsic part of the structure of quasiparallel interplanetary shocks.

Greenstadt, E. W.↗

NASA NTRS1982

The C/H ratio in Jupiter from the Voyager infrared investigation

From a selection Voyager IRIS spectra corresponding to cloud-free areas of Jupiter, the CH4/H2 volume ratio in the atmosphere of this planet has been determined to be equal to 0.00195 + or - 0.00022, which corresponds to 2.07 + or - 0.24 times the solar value of Lambert (C/H = 0.00047). The estimate of errors includes both instrument noise and systematic uncertainties. Implications of this result for the formation and evolution of Jupiter are discussed.

Gautier, D.↗

NASA NTRS1982

Effects of heating rate on density, microstructure, and strength of Si3N4-6 wt.% Y2O3 and a beta-prime sialon

The effects of the heating rate during sintering/firing on the final density, microstructure, and strength of Si3N4-6 wt% Y2O3 and beta-prime sialon, sintered for four hours at 1750 C, are examined. In Si3N4-6 wt% Y2O3 increasing the heating rate from 7 C/min to 25 C/min to 90 C/min results in a corresponding decrease in the final density from 3.01 g/cu cm to 2.92 g/cu cm to 2.76 g/cu cm. In the beta-prime sialon composition all three heating rates produce an equivalent final density of 3.13 g/cu cm. All heating rates in both compositions produce nonhomogeneous microstructures. The room-temperature strength of Si3N4-6 wt% Y2O3 increases from 372 to 510 MPa with increased density, while the corresponding strengths for the betaprime sialon at equivalent densities are 345 to 445 MPa.

Campbell, S. S.↗

NASA NTRS1982

Measurements of outflow from the base of solar coronal holes

New evidence is presented that EUV emission lines formed at the levels of the base of the corona and the transition region are systematically shifted to shorter wavelengths within coronal holes relative to the rest of the solar disk, and that moreover this shift increases with height in the atmosphere. Measurements were made with a rocket-borne EUV spectrometer having high spectroscopic resolution and stability flown on July 15, 1980. Repeated measurements were made along a chord of the solar disk that crossed a compact coronal hole near sun center identified on gamma 10830 He I spectroheliograms. The maximum measured shift corresponded to a velocity of 12 km/sec in gamma 625 Mg X and 7 km/sec in gamma 629 O V. If these velocities correspond to a true mass flux, they provide important data on the acceleration of coronal plasma in open magnetic field regions. These observed Doppler displacements are a strong and significant signature of coronal holes, now measured on three rocket flights.

Rottman, G. J.↗

NASA NTRS1982

Dynamics Explorer observations of equatorial spread F - Evidence for drift waves

Recent DE-2 data from the Langmuir probe, vector electric field, and ion drift meter instruments are employed to study equatorial spread F in the frequency regime of the low frequency drift and the lower hybrid drift instabilities. Strong electron density gradients topside equatorial F region correspond to regions of high electric field waves and large ion drift velocities. The electric field waves are seen in two distinct wavelength ranges which correspond to the parameter regimes of the low frequency drift and the lower hybrid drift instabilities. In the smaller of the two wavelength ranges the lower hybrid drift instability is found to be unstable, based on the ion drift velocity and the other plasma parameters measured on DE-2, and using published theory. Thus there is experimental evidence that the lower hybrid drift instability may produce the observed short wavelength waves without invoking a cascading mechanism.

Hoegy, W. R.↗

NASA NTRS1982

A method for estimation of atmospheric water vapor profiles by microwave radiometry

Simultaneous measurements of microwave emission from the earth, in the oxygen band near 60 GHz, and the water vapor line near 183 GHz are conducted to determine the atmospheric temperature as a function of the pressure and the water vapor burden, and a combination of these two profiles yields a profile of water vapor burden versus pressure. Numerical simulations are developed by using temperature and water vapor profiles from subtropical and midlatitude radiosonde stations, and by assuming surface reflectivities typical of either land or ocean. Over a land surface, the residual rms errors in the estimated water vapor burden profile between 300 and 1000 mb are determined to range from 23 to 43% of the a priori standard deviation of water vapor burden for the corresponding climate. The relative humidity profile is also estimated and found to contain rms errors ranging from 4 to 17% of saturation. Over a seawater surface, using three additional channels of 18.5, 22.2, and 31.7 GHz, the corresponding results are found to be 3-46% of the a priori standard deviation for water vapor burden and 4-15% rms error for relative humidity.

Rosenkranz, P. W.↗

NASA NTRS1982

Hot mantles, moderate photospheres for Wolf-Rayet stars

The amount of continuous energy from Wolf-Rayet stars and the shape of the continuous spectrum from the ultraviolet to the near infrared correspond to effective temperatures in the range 25,000 to 30,000 K. The value of log g is of the order of 4.0 + or - 0.5. Thus the photospheres of Wolf-Rayet stars correspond to those of moderately hot stars. The line spectra of Wolf-Rayet stars, however, indicate that electron temperatures greater than 30,000 K occur in the outer atmospheres or mantles of these stars. Here outflow is important.

Underhill, A. B.↗

NASA NTRS1982

SAGE measurements of Mount St. Helens volcanic aerosols

The SAGE satellite system was used to make measurements on the optical extinction produced by stratospheric aerosols from the Mount St. Helens eruption. Two periods of observation were analyzed. In the first period (May 21 to 31, 1980), SAGE moved southward from latitude 60 N, and crossed the United States approximately one week after the May 18th eruption. Enhancements in stratospheric extinction were confined to latitudes between about 55 N and 25 N and longitudes between 10 W and 140 W. Individual layers were observed up to altitudes of 23 km. The geographical location of these layers corresponded closely to that expected on the basis of high-altitude meteorological data. During June and much of July, SAGE was, by reason of its geographical position and other orbital characteristics, unable to make further measurements on the northern hemisphere. Between July 19th and August 12th a second southward pass over the northern hemisphere occurred and further observations were made. The volcanic aerosol in the stratosphere was now found to be widely distributed over the hemisphere, the maximum concentrations being north of 50 N. The aerosol showed considerable inhomogeneity and had reached as far south as 15 N but little, if any, had crossed the equator into the southern hemisphere. Individual layers at different heights were still distinguishable. The total stratospheric aerosol loading on this occasion appeared to be greater than in May and corresponded to an increase in global stratospheric mass of between 50 and 100 percent.

Kent, G. S.↗