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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Effects of multiple scattering and surface albedo on the photochemistry of the troposphere

The effect of treatment of incoming solar radiation on the photochemistry of the troposphere is discussed. A one dimensional photochemical model of the troposphere containing the species of the nitrogen, oxygen, carbon, hydrogen, and sulfur families was developed. The vertical flux is simulated by use of the parameterized eddy diffusion coefficients. The photochemical model is coupled to a radiative transfer model that calculates the radiation field due to the incoming solar radiation which initiates much of the photochemistry of the troposphere. Vertical profiles of tropospheric species were compared with the Leighton approximation, radiative transfer, matrix inversion model. The radiative transfer code includes the effects of multiple scattering due to molecules and aerosols, pure absorption, and surface albedo on the transfer of incoming solar radiation. It is indicated that significant differences exist for several key photolysis frequencies and species number density profiles between the Leighton approximation and the profiles generated with, radiative transfer, matrix inversion technique. Most species show enhanced vertical profiles when the more realistic treatment of the incoming solar radiation field is included

Augustsson, T. R.↗
NASA NTRS1982

Internal variability of an energy-balance model with delayed albedo effects

A simple, deterministic energy-balance model with possible relevance to climatic variations on the time scale of glaciation cycles, is presented. The lag between ice-sheet extent and zonally-averaged temperature is modeled as a time delay in the ice-albedo feedback. The model exhibits self-sustained oscillations which are quasi-periodic or aperiodic in character. Fourier spectra of solutions have the features of many paleoclimatic records: peaks of variable height and width superimposed on a continuous, red-noise type background.

Bhattacharya, K.↗
NASA NTRS1984

Vegetation, land-use and seasonal albedo data sets: Documentation of archived data tape

Global data bases of vegetation, land use, and land cover were compiled at a 1 deg latitude x 1 deg longitude resolution, drawing on approximately 100 published sources complemented by a large collection of satellite imagery. Six datasets prepared and archived at NCAR are described: a vegetation data set (VEGTYPE) representing natural (pre-agricultural) vegetation based on the UNESCO classification system; a cultivation intensity data set (CULTINT) defining the areal extent (expressed as %) of presently cultivated land in the 1 x 1 cells; and four integrated surface-albedo data sets (January, April, July, October) for snow-free conditions except for permanently snow-covered continental ice, incorporating natural vegetation and cultivation characteristics from the vegetation and cultivation-intensity data sets. Non-zero data are included for permanent land only, including continental ice. Documentation of the data-tape format as well as descriptions and regional maps of the individual data sets are presented.

Matthews, E.↗
NASA NTRS1984

Albedo of a forest modeled as a plane with dense protrusions

An analytical model for the absorption of solar radiation by surfaces such as a pine forest or a wheat field is presented. Objectives include understanding the parameters affecting the absorption of the solar irradiance in a complex structure, and determining the influence of the direction of illumination on light trapping. The surface is treated as a Lambertian reflectivity soil-plane; thin, vertical cylinders are regarded as Lambertian reflectors. Using a dimensionless protrusion parameter based on the height and diameter of the vertical plant elements, optical characteristics (e.g., the dependence of the albedo on the solar zenith angle) of a complex structure are well quantified.

Otterman, J.↗
NASA NTRS1984

Comet Bowell (1980b) - Measurement of the optical thickness of the coma and particle albedo from a stellar occultation

Comet Bowell (1980b) was observed to pass within 0.25 + or 0.09 arc sec of a star (about 540 km at the comet), where the absorption of starlight by the dust coma was found to be 3 percent (+ or - 1 percent). The implied optical thickness of 0.03 differs greatly from other determinations and gives a mass of 3 x 10 to the 13th g for the coma within 10,000 km of the nucleus. Coupled with absolute continuum filter photometry, these results indicate a very low particle albedo consistent with fluffy carbonaceous material. This experiment indicates the need to observe nearly central occultations by several observers to measure the optical thickness profile of a comet. The advantages of using a charge-coupled device area photometer for such observations are discussed.

Larson, S. M.↗
NASA NTRS1985

Atlas of Archived Vegetation, Land-use and Seasonal Albedo Data Sets

Global digital data bases of natural vegetation and land use were compiled, for use in climate studies, at 1 deg resolution from over 100 published sources. A series of 6 data sets, derived from the original compilations, was prepared and archived on tape at the National Center for Atmospheric Research (NCAR) (Matthews, 1984). The first is a vegetation data set representing natural (pre-agricultural) vegetation based on the UNESCO classification system. The second, derived from the land-use compilation, is a cultivation-intensity data set defining the areal extent of presently-cultivated land in the 1 deg cells. The last four are integrated surface-albedo data sets (January, April, July, October) for snow-free conditions, incorporating natural-vegetation and cultivation characteristics from the vegetation and cultivation-intensity data sets. Each of these data sets covers the entire surface of the earth. They include non-zero data for permanent land only, including continental ice; water, including oceans and lakes, is zero. The present report includes maps, presented by continent, of the complete archived data, with the exception of Antarctica.

Matthews, E.↗
NASA NTRS1985

Selection of a model of Earth's albedo radiation, practical calculation of its effect on the trajectory of a satellite

Theoretical models of Earth's albedo radiation was proposed. By comparing disturbing accelerations computed from a model to those measured in flight with the CACTUS Accelerometer, modified according to the results. Computation of the satellite orbit perturbations from a model is very long because for each position of this satellite the fluxes coming from each elementary surface of the terrestrial portion visible from the satellite must be summed. The speed of computation is increased ten times without significant loss of accuracy thanks to a stocking of some intermediate results. Now it is possible to confront the orbit perturbations computed from the selected model with the measurements of these perturbations found with satellite as LAGEOS.

Walch, J. J.↗
NASA NTRS1985

Additional flux of particles and albedo-electrons in upper atmosphere

The results are presented of the Monte Carlo simulation of albedo flux from the dense layers of the Earth's atmosphere and the dependence of angular distribution on the rigidity of geomagnetic cut off and additional flux of particles at the depth in the atmosphere 15-20 g/sq sm. Influence of geomagnetic field on the propagation of charged particles was not taken into account.

Aitbaev, F. B.↗
NASA NTRS1985

Observation of energy spectrum of electron albedo in low latitude region at Hyderabad, India

The preliminary results are presented of the measurement of the energy spectrum of low energy (5-24 MeV) albedo electrons, moving upward as well as downwards, at about 37 km (-4 mb) altitude, over Hyderabad, India, in low latitude region. The flux and energy spectrum was observed by a bi-directional, multidetector charged particle telescope which was flown in a high altitude balloon on 8th December 1984. Results based on a quick look data acquisition and analysis system are presented here.

Verma, S. D.↗
NASA NTRS1984

Modeling crater topography and albedo from monoscopic Viking Orbiter images. I - Methodology

The methodology for a new photoclinometric technique for extracting topographic data from planetary images is described. The technique fully compensates for oblique viewing geometry prevalent in many spacecraft images. Brightness data are taken from a pair of profiles simultaneously, overcoming the problem of albedo variations in the application of photoclinometry to planetary surfaces. An additional procedure is described for eliminating the requirement of topographic symmetry along a pair of profiles. Test results show that both procedures have an accuracy of about two degrees for slopes of typical bowl-shaped craters, or about 5 percent for depths.

Davis, P. A.↗
NASA NTRS1983

Accuracy of earth albedo estimates from wide-angle radiation measurements

The instantaneous resolution and accuracy that can be expected from two inversion techniques to be used in the Earth Radiation Budget Experiment (ERBE) are examined. It is shown that measurement errors are magnified by the numerical filter and that this magnification is a function of the magnitude of the inversion factor. By using singular value decomposition, these magnitudes can be reduced to improve the estimates. A simulation of the estimation process using an albedo field derived from scanning radiometer data shows that retaining 6 of the 13 singular values gives the best results. If there are no bidirectional model errors the medium-field-of-view data give the best estimates. However, when bidirectional model errors are considered, the wide-field-of-view measurements give better estimates since they are less sensitive to these errors.

Green, R. N.↗
NASA NTRS1985

Colour, albedo and nucleus size of Halley's comet

Photometry of Halley's comet in the B, J, V, and K broadband filters during a time when the coma was very weak and presumed to contribute negligibly to the broadband photometry is reported. The V-J and J-K colors suggest that the color of the nucleus of Halley's comet is similar to that of the D-type asteroids, which in turn suggests that the surface of the nucleus has an albedo less than 0.1.

Cruikshank, D. P.↗
NASA NTRS1986

The size, shape, density, and albedo of Ceres from its occultation of BD+8 deg 471

The occultation of BD+8 degrees 471 by Ceres on 13 November 1984 was observed photoelectrically at 13 sites in Mexico, Florida, and the Caribbean. These observations indicate that Ceres is an oblate spheroid having an equatorial radius of 479.6 + or - 2.4 km and a polar radius of 453.4 + or - 4.5 km. The mean density of this minor planet is 2.7 gm/cubic cm + or - 5%, and its visual geometric albedo is 0.070. While the surface appears globally to be in hydrostatic equilibrium, firm evidence of real limb irregularities is seen in the data.

Millis, R. L.↗
NASA NTRS1985

Ultraviolet albedo of cometary grains

Several dusty comets, including two at heliocentric distances greater than 3 AU (Bowell 1982 I and Cernis 1983l), have been observed with the International Ultraviolet Explorer. Ultraviolet albedos have been determined for the wavelength range 2600-3050 A by comparison of the IUE data with both recent solar flux measurements and with IUE observations of solar analog stars. All of the comets show a similar reddening within this spectral range as well as with respect to the visible and infrared. No spectral signatures of possible ices are evident in the data. The ratio of gas to dust production rates, evaluated for 15 comets observed by IUE, shows a well-defined dependence on heliocentric distance.

Feldman, P. D.↗
NASA NTRS1986

Scattering from nonspherical Chebyshev particles. I - Cross sections, single-scattering albedo, asymmetry factor, and backscattered fraction

Using the extended boundary condition method, scattering calculations from randomly oriented rotationally symmetric nonspherical particles were made, the size parameters (1-25) and the refractive indicies (1.5 0.02i) of which were chosen to relate to the transfer of solar and IR radiation in an aerosol atmosphere. Comparison of computations for 23 Chebyshev shapes to corresponding size-averaged spherical results revealed that nonsphericity increased absorption for size parameters larger than around 10 and decreased the asymmetry factor, and correspondingly increased the backscattered fraction, in the size ranges 8-15. The scattering efficiency was somewhat larger for nonspherical particles, while the single-scattering albedo tended to be smaller, and concavity was shown to almost always enhance spherical-nonspherical differences.

Mugnai, A.↗
NASA NTRS1986

Estimates of the bolometric albedos and radiation balance of Uranus and Neptune

Models possessing an upper haze layer of finite optical depth and a lower cloud layer of infinite optical depth at discrete altitudes are used to bound the wavelength-averaged phase integrals and bolometric albedos of Uranus and Neptune. The models differ in the assumed value of the particles' single scattering phase function and the wavelength dependence of the haze optical depth. A range of phase functions, from the isotropic to those characterizing Titan, Jupiter, and Saturn atmosphere particles, are discussed. The results obtained imply that the meteorological regimes in the observable atmospheres of Uranus and Neptune may differ considerably; internal heat flux could play a much more important role for Neptune than for Uranus.

Pollack, J. B.↗
NASA NTRS1986

Parameterization of albedo, thermal inertia, and surface roughness of desert scrub/sandy soil surface

Spectral albedo, A sub n, for the direct solar beam is defined as A sub n (r sub i,s, theta sub 0) = r sub i exp(-s tan theta sub 0)1-I(s) where I(s) is the integral over all reflection angles describing the interception by the absorbing plants of the flux reflected from the soil, r sub i soil reflectance, assumed Lambertian, S the projection on a vertical plane of plants per unit surface area, and theta sub 0 is the solar zenith angle. Hemispheric reflectance for the direct solar beam equals 1-I(s) times the reflectance to the zenith. The values of s of 0.1, 0.2, and 0.3 respectively quantify sparse, moderately dense, and very dense desert scrub. Thin plants are assumed to be of negligible thermal inertia, and thus directly yield the absorbed insolation to the atmosphere. Surface thermal inertia is therefore effectively reduced. The ratio of surface roughness height to plant height is parameterized for sparse, moderately dense, and very dense desert-scrub as a function of s based on data expressing the dependence of this ratio on plant silhouette.

Otterman, J.↗
NASA NTRS1986

A new methodology of determining directional albedo models from Nimbus 7 ERB scanning radiometer measurements

The Nimbus 7 Earth Radiation Budget (ERB) data set is reviewed to examine its strong and weak points. In view of the timing of this report relative to the processing schedule of Nimbus 7 ERB observations, emphasis is placed on the methodology of interpreting the scanning radiometer data to develop directional albedo models. These findings enhance the value of the Nimbus 7 ERB data set and can be applied to the interpretation of both the scanning and nonscanning radiometric observations.

House, Frederick B.↗