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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

A study of the effect of stratospheric aerosols produced by SST emissions on the albedo and climate of the earth

Hypothesized fleets of supersonic aircraft, flying at stratospheric altitude, may lead to a significant increase in the aerosol population of the stratosphere. Exact multiple scattering calculations have been carried out to determine the response of the earth's albedo to an increase of the stratospheric aerosol optical depth. It is found that a tripling of the aerosol population in the stratosphere, which represents an extreme upper limit to the effects of SST's, results in a 0.6% increase of the earth's reflectivity and a decrease of the mean surface temperature on the order of 0.3 K. Such changes could be marginally significant.

Pollack, J. B.↗
NASA NTRS1976

Minor planets and related objects. XX - Polarimetric evidence for the albedos and compositions of 94 asteroids

Polarimetric observations are presented and analyzed for a total of 94 asteroids. The data include numerical parameters describing the polarization-plane curve, the maximum depth of the negative branch, geometric albedo, and diameter. With few exceptions, the polarizations are found to be repeatable from hour to hour, night to night, and apparition to apparition at the same solar phase angle within an observational accuracy of plus or minus 0.05%. It is shown that over a range of more than a factor of 50 in diameter or a factor of 100,000 in mass, all the asteroids seem to have microscopically very rough or particulate surface textures. In terms of their polarimetric properties, the asteroids are classified as follows: 48 in the broad S class, with compositions corresponding to stony-iron meteorites or ordinary chondrites; 34 in the C class, probably corresponding to carbonaceous chondrites; three to five M asteroids with surfaces rich in free metal; two with low-opacity surfaces (class E) attributable to pure enstatite; and five of other types.

Zellner, B.↗
NASA NTRS1977

Contribution to polar albedo from a mesospheric aerosol layer

An examination is made of the impact of a layer of particulate matter, assumed to be ice crystals, on the albedo of the polar region. The model is time dependent, includes the growth of the layer, and incorporates the diffuse nature of radiation reflected from the surface and atmosphere. Although the magnitude of the effect is about an order of magnitude less than previous results, the impact is one of heating instead of cooling. It is also shown that ignoring the diffuse nature of the radiation reflected from the underlying earth-atmosphere system, as has been done in many previous simple models, can result in overestimation of the climatological impact of aerosols in sign and magnitude by a factor of up to 4-6.

Hummel, J. R.↗
NASA NTRS1977

Thermal and Albedo Mapping of Mars During the Viking Primary Mission

The behavior of Mars as observed by the Viking infrared thermal mapper (IRTM) is considered. The IRTM is a 28-channel, 4-telescope radiometer that operated in six spectral bands. The studies considered include observations from the interplanetary phase through data collection on November 7, 1976. During this interval, thermal mapping of the whole Martian surface has been possible. Attention is given to polar temperatures, global albedos, predawn temperatures, a thermal inertia contour map, geometry considerations, clouds, aspects of predawn warming, and observations of earth.

Kieffer, H. H.↗
NASA NTRS1977

Perturbations of a close-earth satellite due to sunlight diffusely reflected from the earth. I - Uniform albedo

A semianalytic method has been developed to calculate the radiation-pressure perturbations of a close-earth satellite due to sunlight reflected from the earth. The assumptions made are that the satellite is spherically symmetric and that the solar radiation is reflected from the earth according to Lambert's Law with uniform albedo. By using expressions for the components of the radiation-pressure force due to Lochry, the expressions for the perturbations of the elements were developed into series in the true anomaly. The perturbations within a given revolution can be obtained analytically by integrating with respect to v while holding all slowly varying quantities constant. The long-range perturbations are then obtained by accumulating the net perturbations at the end of each revolution.

Lautman, D. A.↗
NASA NTRS1977

Sizes and albedos of the larger asteroids

The purpose of the present paper is to review all asteroid diameter measurements, current through mid-1976, and to combine them in a consistent way to give the best available estimates for a sample totalling 187 objects. From these diameters it is possible to determine the size-distributions of minor planets down to diameters of 50 km in the inner belt and 100 km in the outer belt. The associated albedos further indicate the distribution of objects of the C, S, and M classes throughout the belt.

Morrison, D.↗
NASA NTRS1977

Perturbations of a close-earth satellite due to sunlight diffusely reflected from the earth. II - Variable albedo

A semianalytical method has been developed to calculate the radiation-pressure perturbations of a close-earth satellite due to sunlight reflected from the earth. It is assumed that the satellite is spherically symmetric and that the solar radiation is reflected from the earth according to Lambert's law. To account for the increasing reflectivity of the earth toward the poles, its albedo is assumed to have a latitudinal dependence. The effect of the terminator on the perturbations has been neglected. The perturbations within a particular revolution are given analytically, while the long-range perturbations are obtained by accumulation.

Lautman, D. A.↗
NASA NTRS1978

Albedos and size distribution of meteoroids from 0.3 to 4.8 AU

Observational data are compared on the distribution of very small micrometeoroids (1 billionth to 1 hundred-millionth g), the scattering source function of the zodiacal light, the distribution of larger micrometeoroids (at least 1 hundred-thousandth g) as observed from Helios A and Pioneer 10, and the distribution of meteoroids from the sample seen from earth. The experiments, analyses, and simulations involved in obtaining these data are described in detail. It is shown that the various groups of data can be reconciled only by small albedos that decrease outward from 0.1 to at least about 3.3 AU for the particles which produce both the zodiacal light and the observed meteors. The results also indicate that there must be a maximum in the distribution of the larger particles somewhere between the orbits of earth and Jupiter. It is suggested that a search for fireballs in Jupiter's atmosphere by the television cameras of the MJS 77 mission should aid in locating this maximum.

Cook, A. F.↗
NASA NTRS1978

An investigation of surface albedo variations during the recent sahel drought

Applications Technology Satellite 3 green sensor data were used to measure surface reflectance variations in the Sahara/Sahel during the recent drought period; 1967 to 1974. The magnitude of the seasonal reflectance change is shown to be as much as 80% for years of normal precipitation and less than 50% for drought years. Year to year comparisons during both wet and dry seasons reveal the existence of a surface reflectance cycle coincident with the drought intensity. The relationship between the green reflectance and solar albedo is examined and estimated to be about 0.6 times the reflectance change observed by the green channel.

Norton, C. C.↗
NASA NTRS1979

Albedo distribution on Io's surface

A visual albedo distribution model for all hemispheres of Io's surface has been synthesized from available earth-based and spacecraft image and photometric data. The resulting model indicates some interesting patterns and symmetries on Io's surface: the dark polar caps are shifted off Io's rotational axis and are elliptical rather than circular in shape, with extensions toward the sub-Jupiter and anti-Jupiter points on Io; equatorial bright areas are located approximately on a great circle about Io, the plane of which is tilted approximately 15 deg toward Io longitude 60 deg. These and other indicated features may be clues to understanding the endogenic and exogenic processes that have resulted in Io's present observed surface characteristics.

Nash, D. B.↗
NASA NTRS1979

An investigation of surface albedo variations during the recent Sahel drought

Applications Technology Satellite (ATS) 3 green sensor data are used to measure surface reflectance variations in the Sahara/Sahel during the recent drought period 1967-74. The magnitude of the seasonal reflectance change is shown to be as much as 80% for years of normal precipitation and less than 50% for drought years. Year-to-year comparisons during both wet and dry seasons reveal the existence of a surface reflectance cycle coincident with the drought intensity. The relationship between the green reflectance and solar albedo is examined and estimated to be about 0.6 times the reflectance change observed by the green channel.

Norton, C. C.↗
NASA NTRS1979

Jupiter and Saturn - Near-infrared spectral albedos

The near-infrared (0.65-2.5 micron) spectral albedo of Jupiter and Saturn with 1.5% spectral resolution is presented for the center of disk and for the limb. There is a distinct difference in the continuum slope between Jupiter and Saturn which may be attributed to a difference in the dust content or composition of the two atmospheres. There is an indication of limb brightening in the deepest CH4 bands on Saturn. No limb brightening is found for Jupiter.

Clark, R. N.↗
NASA NTRS1980

The effect of a nonuniform planetary albedo on the interpretation of earth radiation budget observations

The flux density measured at satellite altitude with a fixed field of view radiometer differs from the true flux density reflected by the earth-atmosphere system within the field of view of the radiometer. This difference is due to angular response characteristics of the radiometer, solid angle effects due to geometry, and angular reflectance effects of the earth-atmosphere system. All of these effects lead to uncertainties in the interpretation of instantaneous earth radiation budget measurements. The differences between the true flux density and the measured flux density are shown to be significant when the field of view of the radiometer is large and when the atmosphere has a nonuniform, or spatially dependent, reflectance (albedo). A simulation experiment is described whereby the scene within the field of view of a nadir looking sensor is divided into a large number of equal area elements, each of which reflects radiation with one of two different reflectance models (corresponding to cloud-free and cloudy areas). The conditional mean values of the measured flux density, given values of the true flux density, are shown to differ significantly from the conditional means of the inverse problem, that of finding the mean value of the true flux density given a value for the measured flux density. The differences between the true flux density and the measured flux density are examined as a function of satellite altitude, field of view of the radiometer and solar zenith angle (including the effects of a terminator within the field of view) for both Lambertian and non-Lambertian reflectance models.

King, M. D.↗
NASA NTRS1980

Hydrocarbon photochemistry and Lyman alpha albedo of Jupiter

A combined study of hydrocarbon and atomic hydrogen photochemistry is made to calculate self-consistently the L alpha albedo of Jupiter. It is shown that the L alpha emissions observed by Voyagers I and II can be explained by resonance scattering of sunlight. Precipitation of energetic particles from the magnetosphere can provide the large required source of atomic hydrogen, although the contribution of direct particle excitation to the disk-averaged brightness is insignificant. The variability of the L alpha brightness inferred from many observations in recent years is examined. The large difference in the brightness of the He 584 A resonance line observed by Pioneer and Voyager is briefly discussed. Driving the photochemistry by solar ultraviolet radiation alone yields a maximum mixing ratio of C2H6 + C2H2 at 0.01 atm of about 4 x 10 to the -6th. The possibility of additional CH4 dissociation from precipitation of magnetospheric particles is discussed. The photochemistry of C2H2 and C2H3 is sufficiently uncertain not to permit accurate calculations of their densities and the ratio C2H6/C2H2.

Yung, Y. L.↗
NASA NTRS1980

Direct solar and earth-albedo radiation pressure effects on the orbit of Pageos 1

The orbit of the Pageos 1 balloon satellite was analyzed for the effects of direct solar and albedo radiation pressure. Anomalous behavior occurred in the orbital acceleration near the end of the 2nd year of the satellite's lifetime which may have resulted from the change in its shape; the shape has become slightly oblate, spinning about a minor axis and precessing about the direction of the sun. The near-earth micrometeoroid particle flux was estimated to be 5 x 10 to the -8th/sq cm/s by analyzing the balloon inflation process with sublimating compounds and the resulting variation of the satellite mass due to the leakage through the holes produced by micrometeoroid bombardment.

Zerbini, S.↗
NASA NTRS1981

Spectroscopic evidence for aqueous alteration products on the surfaces of low-albedo asteroids

The spectral reflectances of primary components of the carbonaceous chondrite matrix materials (CCMM) and their secondary alteration products are compared with new observations of low-albedo asteroids. It is shown that the spectral differences between C-type asteroids and carbonaceous chondrites are consistent with differing degrees of aqueous alteration of CCMM.

Feierberg, M. A.↗