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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Hydrodynamic models of a Cepheid atmosphere. I - Deep envelope models

The implicit hydrodynamic code of Kutter and Sparks has been modified to include radiative transfer effects. This modified code has been used to compute deep envelope models of a classical Cepheid with a period of 12 days. It is shown that in this particular model the hydrogen ionization region plays only a small role in producing the observed phase lag between the light and velocity curves. The cause of the bumps on the model's light curve is examined, and a mechanism is presented to explain those Cepheids with two secondary features on their light curves. This mechanism is shown to be consistent with the Hertzsprung sequence only if the evolutionary mass-luminosity law is used.

Karp, A. H.↗
NASA NTRS1977

A mathematical study of a random process proposed as an atmospheric turbulence model

A random process is formed by the product of a local Gaussian process and a random amplitude process, and the sum of that product with an independent mean value process. The mathematical properties of the resulting process are developed, including the first and second order properties and the characteristic function of general order. An approximate method for the analysis of the response of linear dynamic systems to the process is developed. The transition properties of the process are also examined.

Sidwell, K.↗
NASA NTRS1977

A reexamination of solar upper photosphere models, the calcium abundance, and empirical damping parameters

A general iterative method is described for constructing thermal models of the solar photosphere consistent with observed strong and weak lines of Ca I and Ca II. Calibrations of the solar calcium abundance and the van der Waals parameter for important Ca I and Ca II lines are obtained using plane-parallel largely LTE model atmospheres, and these thermal models are modified for better fits to the measured Ca II H and K inner wing shapes. Possible sources of error in this semiempirical approach are evaluated. The derived hydrogen van der Waals broadening is compared with theoretical estimates of that broadening as well as with experimental measurements of the helium broadening

Ayres, T. R.↗
NASA NTRS1978

Working model of the atmosphere and near planetary space of Jupiter

Basic physical characteristics of Jupiter, its gravitational field, atmosphere, electromagnetic radiation, magnetosphere, meteorite situation and satellites are presented in tables, graphs and figures. Means of observation of the atmosphere and three models of the atmosphere are presented and analyzed.

Moroz, V. I.↗
NASA NTRS1979

Radiometric resolution for monitoring vegetation: How many bits are needed?

The significance of the various number of radiometric quantizing levels required for satellite monitoring of vegetation resources was evaluated by using in situ collected spectral reflectance data, an atmospheric radiative transfer simulation model, and a satellite sensor simulation model. Reflectance data were converted to radiance data; passed through a model atmosphere to an altitude of 706 km; and subsequently quantized at 16, 32, 64, 128, 256, and 512 digital count levels for Thematic Mapper bands TM3(0.63 - 0.69 microns) and TM4(0.76 - 0.90 microns). The simulated digital count data were regressed against the in situ biological data to quantify the relationship between quantizing levels.

Tucker, C. J.↗
NASA NTRS1979

An investigation of a mathematical model for atmospheric absorption spectra

A computer program that calculates absorption spectra for slant paths through the atmosphere is described. The program uses an efficient convolution technique (Romberg integration) to simulate instrument resolution effects. A brief information analysis is performed on a set of calculated spectra to illustrate how such techniques may be used to explore the quality of the information in a spectrum.

Niple, E. R.↗
NASA NTRS1980

Radiometric resolution for monitoring vegetation - how many bits are needed

The number of radiometric quantizing levels required for satellite monitoring of vegetation resources was evaluated by using in situ collected spectral reflectance data, an atmospheric radiative transfer simulation model, and a satellite sensor simulation model. Reflectance data were converted to radiance data, passed through a model atmosphere to an altitude of 706 km, and subsequently quantized at 16, 32, 64, 128, 256 and 512 digital count levels for Thematic Mapper bands TM3 (0.63-0.69 microns) and TM4 (0.76-0.90 microns). The simulated digital count data were regressed against in situ biological data to quantify the relationship between quantizing levels. Results of the analysis demonstrated that solar zenith angle has an effect on the quantization equivalent change in reflectance, that 256 quantizing levels gave a 1-3% improvement per channel over 64 quantizing levels, and that 256 quantizing levels gave a 1% improvement per channel over 128 quantizing levels. No improvements were found for 256 versus 512 quantizing levels.

Tucker, C. J.↗
NASA NTRS1983

Sensitivity study of orbital atmospheric density models

Results are presented from a parametric study involving the comparison of the sensitivity to changes in the solar flux and geomagnetic index of the three models currently available at the Marshall Space Flight Center, namely J70, J71, and J77. Twelve different cases of solar/geomagnetic input are used in the study. The inputs of each model are the average daily solar flux parameter, the 162-day centered average solar flux parameter, and the 3-hour average geomagnetic index. Values representing solar conditions close to low, medium, and high are used. All the computations are made over an 81-point latitude/longitude earth matrix coonsisting of nine latitudes from 80 deg N to 80 deg S, along with nine longitudes from 40 deg E to 360 deg, with spacing of 20 deg for latitude and 40 deg for longitude.

Johnson, D. L.↗
NASA NTRS1984

A climatically-derived global soil moisture data set for use in the GLAS atmospheric circulation model seasonal cycle experiment

Algorithms for point interpolation and contouring on the surface of the sphere and in Cartesian two-space are developed from Shepard's (1968) well-known, local search method. These mapping procedures then are used to investigate the errors which appear on small-scale climate maps as a result of the all-too-common practice of of interpolating, from irregularly spaced data points to the nodes of a regular lattice, and contouring Cartesian two-space. Using mean annual air temperatures field over the western half of the northern hemisphere is estimated both on the sphere, assumed to be correct, and in Cartesian two-space. When the spherically- and Cartesian-approximted air temperature fields are mapped and compared, the magnitudes (as large as 5 C to 10 C) and distribution of the errors associated with the latter approach become apparent.

Willmott, C. J.↗
NASA NTRS1984

Theory and modeling of atmospheric turbulence, part 1

The cascade transfer which is the only function to describe the mode coupling as the result of the nonlinear hydrodynamic state of turbulence is discussed. A kinetic theory combined with a scaling procedure was developed. The transfer function governs the non-linear mode coupling in strong turbulence. The master equation is consistent with the hydrodynamical system that describes the microdynamic state of turbulence and has the advantages to be homogeneous and have fewer nonlinear terms. The modes are scaled into groups to decipher the governing transport processes and statistical characteristics. An equation of vorticity transport describes the microdynamic state of two dimensional, isotropic and homogeneous, geostrophic turbulence. The equation of evolution of the macrovorticity is derived from group scaling in the form of the Fokker-Planck equation with memory. The microdynamic state of turbulence is transformed into the Liouville equation to derive the kinetic equation of the singlet distribution in turbulence. The collision integral contains a memory, which is analyzed with pair collision and the multiple collision. Two other kinetic equations are developed in parallel for the propagator and the transition probability for the interaction among the groups.

Source record↗
NASA NTRS1984

Theory and modeling of atmospheric turbulence, part 2

Two dimensional geostrophic turbulence driven by a random force is investigated. Based on the Liouville equation, which simulates the primitive hydrodynamical equations, a group-kinetic theory of turbulence is developed and the kinetic equation of the scaled singlet distribution is derived. The kinetic equation is transformed into an equation of spectral balance in the equilibrium and non-equilibrium states. Comparison is made between the propagators and the Green's functions in the case of the non-asymptotic quasi-linear equation to prove the equivalence of both kinds of approximations used to describe perturbed trajectories of plasma turbulence. The microdynamical state of fluid turbulence is described by a hydrodynamical system and transformed into a master equation analogous to the Vlasov equation for plasma turbulence. The spectral balance for the velocity fluctuations of individual components shows that the scaled pressure strain correlation and the cascade transfer are two transport functions that play the most important roles.

Chen, C. M.↗
NASA NTRS1984

Development of a global model for atmospheric backscatter at CO2 wavelengths

Computer graphics software was developed to examine in detail the simulated variations of aerosol size distribution due to gravitational sedimentation effects. This examination contributes to understanding the effect of aerosol microphysical processes occurring in an aerosol plume which undergoes transport in the atmosphere. Results are presented in graphical form. Future research directions are outlined.

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