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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.

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At least 19 records
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NASA NTRS1972

Degree and plane of polarization of multiple scattered light. 2: Earth's atmosphere with aerosols

The degree of polarization, as well as the direction of the plane of polarization, were calculated by a Monte Carlo method for the reflected and transmitted photons from the earth's atmosphere. The solar photons were observed during multiple collisions with aerosols and the Rayleigh scattering centers in the atmosphere. The aerosol number density, as well as the ratio of aerosol to Rayleigh scattering, varies with height. The proportion of aerosol to Rayleigh scattering was appropriately chosen at each wavelength 0.4 microns and 0.7 microns; ozone absorption was included where appropriate. Three different aerosol number densities were used to study the effects of aerosol variations. Results are given for a solar zenith angle of 81.37 deg and a surface albedo of zero. The polarization of the reflected and transmitted photons was found to be sensitive to the amount of aerosols in the atmosphere at certain angles of observation.

Plass, G. N.↗
NASA NTRS1972

Degree and direction of polarization of multiple scattered light. II - Earth's atmosphere with aerosols.

The radiance, polarization, and direction of polarization of the radiation reflected and transmitted through the atmosphere are calculated by a Monte Carlo method on the basis of a realistic model of the atmosphere. The calculated polarization is shown to depend on the aerosol amount and to have normally a value intermediate between that for pure Rayleigh and pure aerosol scattering. The polarization for multiple scattered photons is usually less than the value calculated for single scattering, but may be larger in low-polarization regions near other regions of high polarization. The direction of polarization shows little variation with either the aerosol amount or the value of the surface albedo.

Plass, G. N.↗
NASA NTRS1972

Degree and direction of polarization of multiple scattered light. I - Homogeneous cloud layers.

It is shown that the Monte Carlo method can provide useful information on the polarization and its direction for homogeneous layers corresponding to the haze C, nimbostratus, and ice crystals models. Results for various optical thicknesses and two solar zenith angles show the variation with these parameters. In most cases the direction of polarization with respect to the meridian plane (which contains the outgoing photon) does not change appreciably with the optical thickness of the scattering layer, so that the conclusion that the direction of polarization is determined mainly by the direction of the incident and scattered photons, obtained for single scattering, should apply approximately when multiple scattering is taken into account.

Kattawar, G. W.↗
NASA NTRS1972

Degree and plane of polarization of multiple scattered light. 1: Homogeneous cloud layers

The degree of polarization and the direction of the plane of polarization are calculated by a Monte Carlo method for homogeneous layers. Two solar zenith angles and a range of optical thicknesses up to 10 are considered. The results are compared with calculations for single scattered photons. For a given pair of incident and scattered directions, there are only two possible values for the direction of the plane of polarization differing by 90 deg for single scattering from spherical aerosols. The choice between these two values depends only on the sign of the element M(-) in the first row and second column of the scattering matrix in the I, Q, U, V representation. In most cases there is little change in the direction of the plane of polarization when multiple scattering is taken into account, so that this quantity can usually be predicted from a very simple trigonometric relationship to good accuracy. Measurements of the direction of the plane of polarization at appropriately chosen angles provides information about the size distribution of the scattering centers.

Kattawar, G. W.↗
NASA NTRS1999

Laser Light Scattering with Multiple Scattering Suppression Used to Measure Particle Sizes

Laser light scattering is the technique of choice for noninvasively sizing particles in a fluid. The members of the Advanced Technology Development (ATD) project in laser light scattering at the NASA Lewis Research Center have invented, tested, and recently enhanced a simple and elegant way to extend the concentration range of this standard laboratory particle-sizing technique by several orders of magnitude. With this technique, particles from 3 nm to 3 mm can be measured in a solution. Recently, laser light scattering evolved to successfully size particles in both clear solutions and concentrated milky-white solutions. The enhanced technique uses the property of light that causes it to form tall interference patterns at right angles to the scattering plane (perpendicular to the laser beam) when it is scattered from a narrow laser beam. Such multiple-scattered light forms a broad fuzzy halo around the focused beam, which, in turn, forms short interference patterns. By placing two fiber optics on top of each other and perpendicular to the laser beam (see the drawing), and then cross-correlating the signals they produce, only the tall interference patterns formed by singly scattered light are detected. To restate this, unless the two fiber optics see the same interference pattern, the scattered light is not incorporated into the signal. With this technique, only singly scattered light is seen (multiple-scattered light is rejected) because only singly scattered light has an interference pattern tall enough to span both of the fiber-optic pickups. This technique is simple to use, easy to align, and works at any angle. Placing a vertical slit in front of the signal collection fibers enhanced this approach. The slit serves as an optical mask, and it significantly shortens the time needed to collect good data by selectively masking out much of the unwanted light before cross-correlation is applied.

Meyer, William V.↗
NASA NTRS1993

Multiple scattering of light in a spherical cometary atmosphere with an axisymmetric dust jet. II - Image simulation

A numerical solution for the multiple light scattering in spherical axisymmetric geometry is applied to the simulation of images of a coma as it would appear to a near-flying satellite such as Giotto. The appearance of symmetric comas and dust jets is examined in detail; the nucleus visibility is studied; the effect of forward scattering is considered; and single and multiple scattering effects are quantified. Attention is given to simulated images of a coma with a hollow cone of dust, as predicted by dust-gas hydrodynamic modeling. The cone's appearance is very similar to the northern area of activity on Comet Halley, observed by the Giotto HMC.

Chick, Kenneth M.↗
NASA NTRS1976

Effects of multiple scattering on light pulses reflected by turbid atmospheres

Multiple scattering contributions to lidar returns from turbid atmospheres are derived by means of an analytical theory. It is assumed that scattering takes place mainly at small angles except for one event that scatters the light backward. The phase functions are approximated by the sum of Gaussian functions of the scattering angle in both the forward and backward directions. The three-dimensional radiative transfer equation is transformed to a one-dimensional problem by means of Fourier transforms. Neumann solutions to the transformed equation of radiative transfer are then found. A number of examples are presented for cloud, fog and haze models. The results are found to be in satisfactory agreement with results obtained from the Monte Carlo analysis of Kunkel (1974) and the theory of light pulses doubly scattered by turbid atmospheres which was developed by Eloranta (1972).

Weinman, J. A.↗
NASA NTRS1992

Multiple scattering of light in a spherical cometary atmosphere with an axisymmetric dust jet

A numerical solution has been developed for the anisotropic multiple scattering of light in a spherical shell comet atmosphere. The code has been run for a spherically symmetric coma distribution, benchmarked against past studies, and then run for the conditions of an axisymmetric dust jet at the subsolar point of the comet. The radiant flux impinging on the nucleus surface and the mean intensity of light throughout the coma were investigated.

Chick, Kenneth M.↗
NASA NTRS1980

Investigation of numerical properties of Hovenier's exit function equation for multiple scattering of light

A technique of deriving Hovenier's exit function equation (1978) for multiple scattering, starting with a set of invariant imbedding equations, is presented. The feasibility of the exit function equation as a means to obtain reflection and transmission functions is investigated for isotropic, Rayleigh, and Henyey-Greenstein phase functions with emphasis on the numerical stability, accuracy and timing. It is possible to compute the reflection function rather accurately with an efficiency comparable to that of the standard doubling technique for the same phase functions with moderate anisotropy. The resulting transmission is slightly less accurate than the reflection function, but it may be acceptable for practical purposes.

Kawabata, K.↗
NASA NTRS1997

Microgravity Foam Structure and Rheology

To exploit rheological and multiple-light scattering techniques, and ultimately microgravity conditions, in order to quantify and elucidate the unusual elastic character of foams in terms of their underlying microscopic structure and dynamics. Special interest is in determining how this elastic character vanishes, i.e. how the foam melts into a simple viscous liquid, as a function of both increasing liquid content and shear strain rate. The unusual elastic character of foams will be quantified macroscopically by measurement of the shear stress as a function of static shear strain, shear strain rate, and time following a step strain; such data will be analyzed in terms of a yield stress, a static shear modulus, and dynamical time scales. Microscopic information about bubble packing and rearrangement dynamics, from which these macroscopic non-Newtonian properties presumably arise, will be obtained non-invasively by novel multiple-light scattering diagnostics such as Diffusing-Wave Spectroscopy (DWS). Quantitative trends with materials parameters, such as average bubble size, and liquid content, will be sought in order to elucidate the fundamental connection between the microscopic structure and dynamics and the macroscopic rheology.

Durian, Douglas J.↗
NASA NTRS1996

Multiple-Fiber-Optic Probe For Light-Scattering Measurements

Multiple-fiber-optical probe developed for use in measuring light scattered at various angles from specimens of materials. Designed for both static and dynamic light-scattering measurements of colloidal dispersions. Probe compact, rugged unit containing no moving parts and remains stationary during operation. Not restricted to operation in controlled, research-laboratory environment. Positioned inside or outside light-scattering chamber. Provides simultaneous measurements at small angular intervals over range of angles, made to include small scattering angles by orienting probe in appropriate direction.

Dhadwal, Harbans Singh↗