SEARCH · Search NASA

Results for “reflection”

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.

SourceResearch connectionFrom yearThrough year

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

At least 613 records · Page 34

All sources NASA NTRS DOE OSTI

NASA NTRS1977

Asteroid infrared reflectances and compositional implications

The paper assesses the state of asteroid infrared reflectance measurements and discusses what they have contributed to our understanding of asteroidal surfaces. The data suggest that space weathering has not significantly affected the optical properties of the asteroids. Thus comparisons of asteroid reflectance spectra with unweathered meteorite and rock data is a valid procedure. The high 1.6 and 2.2 micron reflectances of a number of asteroids strongly suggest the presence of a metallic phase.

Matson, D. L.↗

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 NTRS1977

A practical method for correcting bidirectional reflectance variations

The purpose of the investigation was to analyze angular bidirectional reflectance variations and to test the hypothesis that first order variations could be described from a consideration of shadows created by surface perturbations. The results demonstrate the validity of this approach, and while it is not suitable for calculating absolute spectral reflectance characteristics, the development of such a model was not the objective of the investigation. Instead, a model was needed which can make relative angular corrections to bidirectional reflectance measurements independent of the details of surface geometry.

Egbert, D. D.↗

NASA NTRS1978

Lunar occultation of Saturn. II - The normal reflectance of Rhea, Titan, and Iapetus

An inversion procedure to obtain the reflectance of the central region of a satellite's disk from lunar occultation data is presented. The scheme assumes that the limb darkening of the satellite depends only on the radial distance from the center of the disk. Given this assumption, normal reflectances can be derived that are essentially independent of the limb darkening and the diameter of the satellite. The procedure has been applied to our observations of the March 1974 lunar occultation of Tethys, Dione, Rhea, Titan, and Iapetus. In the V passband we derive the following normal reflectances: Rhea (0.97 plus or minus 0.20), Titan (0.24 plus or minus 0.03), Iapetus, bright face (0.60 plus or minus 0.14). For Tethys and Dione the values derived have large uncertainties, but are consistent with our result for Rhea.

Elliot, J. L.↗

NASA NTRS1977

Effects of atmosphere, temperature and emittance on reflected and emitted energy

The effects of temperature and emittance on the relative magnitude of reflected energy and emitter energy from a target including atmospheric effects was studied. From the calculations of energy reflected and emitted from a target including atmospheric effects using LOWTRAN 3 programs for midlatitude summer model, the following conclusions were obtained: (1) At 3.5 micrometers q is considerably less than 1 except at high temperatures and for high emittance; (2) at 4 micrometers q is of the order of magnitude equal to 1 for most targets; and (3) at 4.6 micrometers, q is considerably greater than 1 at high temperatures and high emittance. In addition, incident atmospheric emission reflected from the target was found to be negligible except for targets having low temperature and low emittance.

Kumar, R.↗

NASA NTRS1978

Two-stream theory of spectral reflectance of snow

Spectral reflectance of snow under diffuse illumination is studied using the two-stream approximation of the radiative transfer equation. The scattering and absorption within the snowcover due to the randomly distributed ice grains are characterized by the single scattering albedo and anisotropic phase function. Geometric optics calculations are used to relate the scattering and absorption parameters to grain size and density of snow. Analytical expressions for the intensity within the snowpack and the asymptotic flux extinction coefficient are also obtained. Good agreement is shown between the theory and available experimental data on visible and near-infrared reflectance and asymptotic flux extinction coefficient. The theory also may be used to explain the observed effect of aging on the snow reflectance.

Choudhury, B. J.↗

NASA NTRS1979

The reflectance characteristics of snow covered surfaces

Data analysis techniques were developed to most efficiently use available satellite measurements to determine and understand components of the surface energy budget for ice and snow-covered areas. The emphasis is placed on identifying the important components of the heat budget related to snow surfaces, specifically the albedo and the energy consumed in the melting process. Ice and snow charts are prepared by NOAA from satellite observations which map areas into three relative reflectivity zones. Field measurements are analyzed of the reflectivity of an open snow field to assist in the interpretation of the NOAA reflectivity zones.

Batten, E. S.↗

NASA NTRS1979

Interpreting vegetation reflectance measurements as a function of solar zenith angle

Spectral hemispherical-conical reflectances of a nadir looking sensor were taken throughout the day for a lodgepole pine and two grass canopies. Mathematical simulations of both spectral hemispherical-conical and bi-hemispherical reflectances were performed for two theoretical canopies of contrasting geometric structure. These results and comparisons with literature studies showed a great amount of variability of vegetation canopy reflectances as a function of solar zenith angle. Explanations for this variability are discussed and recommendations for further measurements are proposed.

Kimes, D. S.↗

NASA NTRS1978

Using reflectance and photography to detect ozone damage to cantaloupe plants

Laboratory and field reflectance measurements showed that ozone-damaged cantaloupe (Cucumis melo L.) leaves had lower water contents and higher reflectance than nondamaged leaves. Cantaloupe plants with lightly, severely, and very severely ozone-damaged leaves were distinguishable from nondamaged plants by reflectance measurements in the 1.35-2.5-micron near-IR water absorption band. Ozone-damaged leaf areas were detected photographically 16 hours before the damage was visible.

Gausman, H. W.↗

NASA NTRS1979

Polarization-sensitive spectroradiometer - Two methods for overcoming the problems of measuring reflectance spectra

The spectra obtained using a spectroradiometer are incorrect if the incident light from the sample is polarized, and if, at the same time, polarization is introduced into the transmitted beam by components of the spectroradiometer. Two methods are proposed for obtaining correct power reflectance spectra. One way is to average two incorrect reflectance spectra, which are taken at mutually orthogonal angles of rotation of the radiometer about its optical axis. Another way is by averaging reflectance spectra of mutually orthogonal polarized light components. When the orientation of one component is chosen such that it is in the plane of polarization of the incoming light, the latter method also gives the correct degree of polarization.

Auer, S.↗

NASA NTRS1978

A low cost, durable anti-reflective film for solar collectors

The physics of reflection reduction by thin films is briefly reviewed. Current techniques for the production of anti-reflective coatings are surveyed with respect to their applicabilities to solar panel covers. Techniques for the production of suitable anti-reflection coatings based on acid-hardened sodium silicate solutions are presented along with optical data for both acid-leached and silicate coatings

Pastirik, E. M.↗

NASA NTRS1979

Planetary reflectance measurements in the region of planetary thermal emission

As planetary reflectance measurements are extended into the infrared, the emitted thermal radiation becomes larger than the reflected solar component. This paper describes a method for removal of the thermal component from planetary reflectance measurements and discusses the limitations involved. Examples are shown for the case of lunar observations where the temperature and emissivity are known and for Mercury where it is assumed the temperature and emissivity are unknown

Clark, R. N.↗

NASA NTRS1979

Atlas of soil reflectance properties

A compendium of soil spectral reflectance curves together with soil test results and site information is presented in an abbreviated manner listing those soil properties most important in influencing soil reflectance. Results are presented for 251 soils from 39 states and Brazil. A narrative key describes relationships between soil parameters and reflectance curves. All soils are classified according to the U.S. soil taxonomy and soil series name for ease of identification.

Stoner, E. R.↗

NASA NTRS1980

Physiochemical, site, and bidirectional reflectance factor characteristics of uniformly moist soils

The author has identified the following significant results. The bidirectional reflectance factor (0.5 micron to 2.3 micron wavelength interval) and physiochemical properties of over 500 soils from 39 states, Brazil and Spain were measured. Site characteristics of soil temperature regime and moisture zone were used as selection criteria. Parent material and internal drainage were noted for each soil. At least five general types of soil reflectance curves were identified based primarily on the presence or absence of ferric iron absorption bands, organic matter content, and soil drainage characteristics. Reflectance in 10 bands across the spectrum was found to be negatively correlated with the natural log of organic matter content.

Stoner, E. R.↗

NASA NTRS1979

An efficient approach for computing the geometrical optics field reflected from a numerically specified surface

An approach for computing the geometrical optic fields reflected from a numerically specified surface is presented. The approach includes the step of deriving a specular point and begins with computing the reflected rays off the surface at the points where their coordinates, as well as the partial derivatives (or equivalently, the direction of the normal), are numerically specified. Then, a cluster of three adjacent rays are chosen to define a 'mean ray' and the divergence factor associated with this mean ray. Finally, the ampilitude, phase, and vector direction of the reflected field at a given observation point are derived by associating this point with the nearest mean ray and determining its position relative to such a ray.

Mittra, R.↗

NASA NTRS1980

Dependence of the spectral surface irradiance on aerosol properties and surface reflectivity

A reduction in global surface irradiance occurs with increasing aerosol loadings when the aerosols are absorbing. For scattering aerosols, a reduction is pronounced for isotropic scattering (characteristic of small particles) but reduction is not as significant for scattering with a high anisotropy of a large forward peak (characteristic of large particles). This distinction between isotropic and anisotropic scattering becomes small or null over highly reflecting terrain; and for reflectivities higher than 0.5 and solar elevation angles close to the zenith, the global irradiance can be slightly higher for isotropic scattering than in the case of an anisotropy of a forward peak. Under such conditions, which can be encountered in reflective infrared bands over dense vegetation or over sandy deserts (close to noon, in low latitudes) the surface irradiance becomes nearly independent of the aerosol optical thickness.

Otterman, J.↗

NASA NTRS1980

The relative reflectance of Iapetus at 1.6 and 2.2 microns

Iapetus was observed at 0.56, 1.6, and 2.2 microns near seven elongations. The infrared reflectance at 2.2 microns relative to 0.56 microns varies from 0.6 to 1.6 (plus or minus 0.1). The low infrared reflectance of the trailing hemisphere of Iapetus is consistent with the previous identification of water ice as the composition of the bright surface. The high infrared reflectance of the leading hemisphere indicates a dark material that is too red to be consistent with a carbonaceous chondritic or 'C'-type surface composition.

Veeder, G. J.↗

NASA NTRS1980

Cost/performance of solar reflective surfaces for parabolic dish concentrators

Materials for highly reflective surfaces for use in parabolic dish solar concentrators are discussed. Some important factors concerning performance of the mirrors are summarized, and typical costs are treated briefly. Capital investment cost/performance ratios for various materials are computed specifically for the double curvature parabolic concentrators using a mathematical model. The results are given in terms of initial investment cost for reflective surfaces per thermal kilowatt delivered to the receiver cavity for various operating temperatures from 400 to 1400 C. Although second surface glass mirrors are emphasized, first surface, chemically brightened and anodized aluminum surfaces as well as second surface, metallized polymeric films are treated. Conventional glass mirrors have the lowest cost/performance ratios, followed closely by aluminum reflectors. Ranges in the data due to uncertainties in cost and mirror reflectance factors are given.

Bouquet, F.↗