Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Albedo”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Surface features on Mars - Ground-based albedo and radar compared with Mariner 9 topography

Earth-based albedo maps of Mars were compared with Mariner 9 television data and ground-based radar profiles to investigate the nature of the bright and dark albedo features. Little correlation was found except at the boundaries of classical albedo features, where some topographic control is indicated. Windblown dust models for seasonal and secular albedo variations are supported, but it is not clear whether the fines are derived from bright or dark parent rock. Mars, like the earth and moon, has probably generated two distinct types of crustal material.

Frey, H.↗
NASA NTRS1976

Martian albedo feature variations with season - Data of 1971 and 1973

A qualitative and quantitative study of some recent seasonal and secular albedo variations on Mars is presented, based on improved red-filter photographs obtained during the 1971 and 1973 apparitions. The measurement of albedo features showing significant changes and uncommonly bright areas is described in detail. Photographic differential photometry of 21 albedo features in three longitude regions is also discussed. The major findings are: (1) seasonal differences of the mean brightness ratios for most features were consistent with contrast changes shown on photographic maps, (2) seasonal variations of brightness with latitude and region occurred, (3) most albedo features were more variable during southern spring than summer, (4) a general loss of relative contrast was experienced during southern summer, and (5) no systematic dependence on solar phase angle was detected within the range spanned by both sets of photographs. Possible causes of the variations are considered.

Capen, C. F., Jr.↗
NASA NTRS1977

Radii and albedos of four Trojan asteroids and Jovian satellites 6 and 7

Results are reported for radiometric measurements of broadband 20-micron fluxes from the Trojan asteroids 617 Patroclus, 624 Hektor (for which the broadband 10-micron flux was also measured), 1172 Aeneas, and 1173 Anchises as well as from the outer Jovian satellites Himalia (J6) and Elara (J7). Geometric albedos and radii for the six objects are derived from the corrected monochromatic fluxes and visual magnitudes. It is found that all the objects have exceedingly low geometric albedos, indicating that the Trojans and possibly the outer Jovian satellites constitute a distinct class of small solar-system bodies. The composition of the Trojan asteroids is considered on the basis of available sizes, albedos, and shapes. Revised tables of the albedos and radii of all the Jovian satellites are presented. It is concluded that the Trojans are not composed primarily of ice and that an asteroidal origin for the comets of the Jupiter group is unlikely.

Cruikshank, D. P.↗
NASA NTRS1977

The extreme ultraviolet albedos of the planet Mercury and of the moon

The albedo of the moon in the far UV was measured by Mariner 10 at a solar phase angle of 74 deg, and the geometric albedo of Mercury was measured in same wavelength range (584-1657 A) at solar phase angles ranging from 50 to 120 deg. For both the moon and Mercury there is a general increase in albedo for wavelengths decreasing from 1657 to 584 A. The ratio of the albedos of Mercury and the moon increases from about 0.6 to 0.8 in the range 600-1600 A. This merely points to a difference in the surfaces of the moon and Mercury, there being insufficient data to make any conclusions regarding the nature of the difference.

Wu, H. H.↗
NASA NTRS1977

Asteroid sizes and albedos

The radiometric method of determining asteroid diameters is described, and a synthesis of radiometric and polarimetric measurements of the diameters and geometric albedos of a total of 187 asteroids is presented. An analysis is offered of the size distributions of different albedo classes down to 80-km diameter for the entire main asteroid belt (2.0-3.5 AU). The distribution of albedos is found to be strongly bimodal, with mean albedos for the C and S group of 0.035 and 0.15, respectively. The C asteroids outnumber the S asteroids at all sizes and all values of semimajor axis, with the proportion of C asteroids increasing from a little over half inside 2.5 AU to more than 95% beyond 3.0 AU. Other aspects of the distribution of C, S, and M asteroids are discussed, and the total mass of main-belt asteroids larger than 70 km is estimated.

Morrison, D.↗
NASA NTRS1977

The surface abundance and stratigraphy of lunar rocks from data about their albedo

The data pf ground-based studies and surveys of the lunar surface by the Zond and Apollo spacecraft have been used to construct an albedo map covering 80 percent of the lunar sphere. Statistical analysis of the distribution of areas with various albedos shows several types of lunar surface. Comparison of albedo data for maria and continental areas with the results of geochemical orbital surveys allows the identification of the types of surface with known types of lunar rock. The aluminum/silcon and magnesium/silicon ratios as measured by the geochemical experiments on the Apollo 15 and Apollo 16 spacecraft were used as an indication of the chemical composition of the rock. The relationship of the relative aluminum content to the age of crystalline rocks allows a direct dependence to be constructed between the mean albedo of areas and the age of the rocks of which they are composed.

Shevchenko, V. V.↗
NASA NTRS1977

A comparative study of the effects of albedo change on drought in semi-arid regions

Numerical simulation studies of the effects of changes in albedo on rainfall involve comparisons of semiarid areas, lying at the boundary between a major desert and an adjacent monsoonal region, with areas of the same size located within the monsoonal region itself. The sensitivity of the rainfall to the ground hydrology was determined by performing the albedo simulations with two different evapotranspiration parameterizations, one giving too high evaporation over land and the other giving negligible evaporation over land. The evaporation rate is, in general, found to have as important an effect as changes in albedo. The mechanism by which an increase of albedo reduces the rainfall during conditions of high evaporation is considered.

Charney, J.↗
NASA NTRS1979

The radius and albedo of Hyperion

A measurement of the 20-micron thermal flux from Hyperion is reported, and the radius and surface geometric albedo of this outer satellite of Saturn are computed by the photometric/radiometric method. A corrected and normalized 20-micron thermal flux of 0.033 + or - 0.012 Jy is determined. A radius of 112 + or - 15 km and a surface geometric albedo of 0.47 + or - 0.11 are obtained by assuming values of unity for the phase integral, emissivity, and bolometric/visual geometric-albedo ratio. The sensitivity of the photometric/radiometric method to the assumed values of the parameters involved is discussed, and the results are compared with similar studies of Triton. It is concluded that neither Hyperion nor Triton appears to have a geometric albedo in the lower end of the distribution of small bodies in the solar system.

Cruikshank, D. P.↗
NASA NTRS1980

The seasonal cycle of snow cover, sea ice and surface albedo

The paper examines satellite data used to construct mean snow cover caps for the Northern Hemisphere. The zonally averaged snow cover from these maps is used to calculate the seasonal cycle of zonally averaged surface albedo. The effects of meltwater on the surface, solar zenith angle, and cloudiness are parameterized and included in the calculations of snow and ice albedo. The data allows a calculation of surface albedo for any land or ocean 10 deg latitude band as a function of surface temperature ice and snow cover; the correct determination of the ice boundary is more important than the snow boundary for accurately simulating the ice and snow albedo feedback.

Robock, A.↗
NASA NTRS1980

Ultraviolet albedo of Comet West /1976 VI/

The nature of the dust scattered radiation shown in the ultraviolet spectrum of Comet West is analyzed. The continuum of solar radiation scattered by cometary dust is detected to wavelengths as short as 2100 A and is found to follow closely the solar spectrum. The flux from the entire visible coma is included in the spectrometer slit. A comparison of the ultraviolet with the visible solar flux gives the ratio of the albedo at 2700 A to that of 5500 A as about 0.3. Even with all the uncertainties included (the absolute calibration uncertainty is plus or minus 15%), the evidence for strong reddening between the visible and the ultraviolet is clear. A further decrease in albedo is found near 2200 A. The value of the visible albedo of 0.2 is used to derive a value of 0.6 for the cometary albedo at 2700 A. This value is similar to that found for the moon and lunar dust in this spectral region.

Feldman, P. D.↗
NASA NTRS1981

The albedo of snow for partially cloudy skies

The albedo of snow is defined as the ratio of reflected to incident solar energy, and it is an important parameter in the earth's radiation budget analysis and in the study of snowpack's thermal conditions. An approximate model for calculating the incident spectral flux for partially cloudy skies is presented. The input parameters for the calculation are atmospheric precipitable water, turbidity, ozone content, surface pressure, the optical thickness of clouds, and the grain size of snow crystals. The spectral snow reflectance model considers both specular surface reflection and volumetric multiple scattering. The surface reflection is calculated by using a crystal-shape-dependent bidirectional reflectance distribution function; the volumetric multiple scattering is calculated by using a crystal-size-dependent approximate solution in the radiative transfer equation. The model yields spectral and integrated solar flux and snow reflectance as a function of solar elevation and fractional cloud-cover. The illustrative insolation and albedo values were obtained from spectral reflectance and incident flux for representative parameters of Antarctic coastal regions. A simple relationship between grain size and the overcast albedo was obtained. For a set of grain size and shape, the albedo as a function of solar elevation and fractional cloud cover was tabulated.

Choudhury, B. J.↗
NASA NTRS1981

Influence of surface-albedo in subtropical regions on July circulation

A simulation study to examine the influence of surface-albedo on July circulation in subtropical regions is presented. The results are based on two 47-day integrations. In the first integration, called the control run, surface albedos were normally prescribed, whereas in the second integration, called the anomaly run, the surface albedo was modified in four regions: the Sahel in Africa, the Great Plains in the United States, the Thar Desert border in the Indian subcontinent, and Brazil in South America. Each run was started from observed initial conditions for June 15, 1979 based on NMC analysis. The surface albedo in each of the regions was arbitrarily made 30%.

Sud, Y.↗
NASA NTRS1982

Determination of surface albedos and aerosol extinction characteristics from satellite imagery

A procedure is developed for calculating atmospheric extinction characteristics (optical thickness, scattering height, single scattering albedo) and surface albedo from radiometric images made at satellite altitudes. The procedure - a fast, computerized method - is suitable for the high-volume processing of satellite imagery data and thus can be used to map temporal and spatial distributions of aerosol parameters. Based on an analytical approximate solution to the equation of radiative transfer in a plane parallel atmosphere, the procedure is primarily applicable to the 0.4-micron to 0.8-micron wavelength range for solar zenith angles from 10 deg to 60 deg, surface albedos between 0.03 and about 0.5, and atmospheric optical thicknesses from 0.2 to 2. With a step-like change in the surface albedo (for example, a seashore or river bank or other similar change of terrain), both surface reflectivity and atmospheric optical thickness can be derived from radiance measurements. In this case, the resultant optical thickness is not based on a known surface reflectivity and is in essence independent of the radiometer calibration.

Kaufman, Y. J.↗
NASA NTRS1983

A preliminary global oceanic cloud climatology from satellite albedo observations

A predictive relationship is developed between over-ocean cloud system albedo and the cloud amount present, using as a data base ERB satellite microwave readings at 0.5-0.7 micron and the USAF three-dimensional nephanalysis archive. The ERB data provided global coverage at a resolution of 2.5 x 2.5 deg during the 1974-78 period. Regression analyses were performed on the amounts and albedos for several years of data for one month in order to detect seasonal variations. A logarithmic relationship was found between the cloud system albedo and cloud amount over the oceans, with negligible seasonal variance. The analysis is noted to apply only where low surface albedos are encountered, and further work to extend the study to continental vegetated areas is indicated.

Hughes, N. A.↗
NASA NTRS1984

Slant-lidar aerosol extinction measurements and their relation to measured and calculated albedo changes

Lidar and albedo data for a single day on which aerosols increased the surface plus atmospheric albedo above values measured on two surrounding very clean days are presented. The slant-lidar extinction measurement technique used is described along with the equipment and operating procedures. The derivation of optical depths, backscatter-to-extinction ratios, and extinction profiles is addressed, and the use of the lidar-derived optical depths in calculating expected albedo change is considered. Measured and calculated albedo changes are compared, and the results are found to agree within experimental uncertainties.

Russell, P. B.↗
NASA NTRS1984

Measuring planetary neutron albedo fluxes by remote gamma-ray sensing

In order to measure the planetary neutron albedo fluxes, a neutron-absorbing shield which emits gamma rays of characteristic energy and serves as a neutron detector, is added to a gamma-ray spectrometer (GRS). The gamma rays representing the neutron flux are observed against interference consisting of cosmic gamma rays, planetary continuum and line emission, and gamma rays arising from the interaction of cosmic rays with the GRS and the spacecraft. The uncertainty and minimum detection limits in neutron albedo fluxes are calculated for two missions, a lunar orbiter and a comet nucleus rendezvous. A GRS on a lunar orbiter at 100 km altitude detects a thermal neutron albedo flux as low as 0.002/sq cm/s and an expected flux of about 0.6/sq cm/s is measured with an uncertainty of 0.001/sq cm/s, for a 100 h observation period. For the comet nucleus, again in a 100 h observing period, a thermal neutron albedo flux is detected at a level of 0.006/sq cm/s and an expected flux of about 0.4/sq cm/s is measured with an uncertainty of 0.004/sq cm/s. The expanded geological capabilities made possible by this technique include improvements in H sensitivity, spatial resolution, and measurement depth; and an improved model of induced gamma-ray emission.

Haines, E. L.↗
NASA NTRS1986

Comparison of ERBE inferred and model computed clear-sky albedos

Over-ocean clear-sky albedos measured with instruments on the Earth Radiation Budget Satellite (ERBS) are compared with albedos simulated using a radiative transfer model (RTM). The comparison covers the monthly mean albedos for November 1984. The ERBS albedo was calculated with a scene identification algorithm. Techniques used to suppress cloud cover uncertainties are discussed. The plane-parallel delta-Eddington RTM accounted for O3, O2, CO2 and H2O gaseous absorption and background aerosol absorption.

Briegleb, B. P.↗
NASA NTRS1987

Seasonal albedo of an urban/rural landscape from satellite observations

Using data from 27 calibrated Landsat observations of the Hartford, Connecticut area, the spatial distribution and seasonal variation of surface reflectance and albedo were examined. Mean values of visible reflectance, near-IR reflectance, and albedo are presented (for both snow-free and snow-cover observations) according to 14 land use/land cover categories. A diversity of albedo values was found to exist in this type of environment, associated with land cover. Many land-cover categories display a seasonal dependence, with intracategory seasonal differences being of comparable magnitude to intercategory differences. Key factors in determining albedo (and its seasonal dynamics) are the presence or absence of vegetation and the canopy structure. Snow-cover/snow-free differences range from a few percent (for urban land covers) to over 40 percent (for low-canopy vegetation).

Brest, Christopher L.↗