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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1970

Some properties of unstable particle gases

Elastic scattering formation and decay of unstable particle gases, discussing density and corrections to chemical and nuclear statistical equilibrium equations

Delano, M. D.↗
NASA NTRS1981

Properties of dust particles in Comet Halley from observations made in 1910 during its encounter with the Earth

Observations of the dust tail of Comet Halley about the time of the Earth's transit across the orbit plane of the comet are analyzed. The Earth grazed the tail, whose apparent length reached up to 150 deg. The maximum acceleration the ejecta were subjected to by solar radiation pressure is approximately 2.5 times the solar attraction. This acceleration indicates the presence of submicron sized, strongly absorbing particles. Their detectable contribution to the tail's brightness is limited to the immediate proximity of the orbit plane because of a low reflectivity and/or a low spatial density. The width of the tail, observed edgewise at the time of transit, is determined by particles whose beta = 05, possibly submicron sized dielectric grains. Their derived ejection velocity = 450 m/sec.

Sekanina, Z.↗
NASA NTRS1987

Timing of frost deposition on Martian dunes: A clue to properties of dune particles?

Scans were made across the Martian dunes found in images taken at several different times to determine the time history of the dune albedo. Atmospheric contributions were estimated using optical depth data and the brightness of shadows in some images. The data show that the dunes brighten very substantially between L(s) = 10 and 40 deg, depending on the latitude. Bright coverings on dunes form outliers 1 to 5 deg north of the cap edge. Formation of the general cap then sometimes reverses the contrast of the dune field with the surrounding area. Causes for the early deposition of frost on dunes relative to surroundings are discussed.

Thomas, P.↗
NASA NTRS1995

Temperature measurements of a Martian local dust storm

A technique for estimating the ground and near-ground atmospheric temperatures within a Martian local dust storm is presented. It is applied to soundings taken by the Viking orbiter infrared thermal mapper (IRTM) instrument at four times-of-day for one storm. Essentially, a comparison is made between infrared radiances emerging from the storm interior and those from the region surrounding the storm. Particle extinction properties are assumed to be independent of position in the storm region, and scattering properties must be selected arbitrarily. For the storm studied here, the ground temperature in the interior is at least 6 K cooler, whereas the near-ground atmospheric temperature may be less than or comparable to, those of the surroundings. The thermal structure of the storm interior did not change measurably between 11.5 and 16.6 hours local time. These observations favor the theories of dust storm development in which regional winds rather than local, dust driven convection initiate the mobilization of dust from the surface. It also concluded that the optical properties of dust particles in this local storm differ from those observed by Mariner 9 during the 1971-1972 global dust storm.

Kahn, Ralph↗
NASA NTRS1995

Temperature measurements of a Martian local dust storm

A technique for estimating the ground and near-ground atmospheric temperatures within a Martian local dust storm is presented. It is applied to soundings taken by the Viking orbiter infrared thermal mapper (IRTM) instrument at four times-of-day for one storm. Essentially, a comparison is made between infrared radiances emerging from the storm interior and those from the region surrounding the storm. Particle extinction properties are assumed to be independent of position in the storm region, and scattering properties must be selected arbitrarily. For the storm studied here, the ground temperature in the interior is at least 6 K cooler, whereas the near-ground atmospheric temperature may be less than or comparable to, those of the surroundings. The thermal structure of the storm interior did not change measurably between 11.5 and 16.6 hours local time. These observations favor theories of dust storm development in which regional winds rather than local, dust-driven convection initiate the mobilization of dust from the surface. It is also concluded that the optical properties of dust particles in this local storm differ from those observed by Mariner 9 during the 1971-1972 global dust storm.

Kahn, Ralph↗
NASA NTRS1997

Measurement of Optical Properties of Small Particles

We have measured the optical constants of montmorillonite and the separated coats and cores of B. subtilis spores over the wavelength interval from 200 nm to 2500 nm. The optical constants of kaolin were obtained over the wavelength interval from 130 nm to 2500 nm. Our results are applicable to the development of systems for detection of airborne biological contaminants. Future work will include measurement of the optical constants of B. cereus spores, B. sub tilts vegetative cells, egg albumin, illite, and a mixture (by weight) of one third kaolin, one third montmorillonite, and one third illite.

Arakawa, E. T.↗
NASA NTRS2009

Spectral Absorption Properties of Aerosol Particles from 350-2500nm

The aerosol spectral absorption efficiency (alpha (sub a) in square meters per gram) is measured over an extended wavelength range (350 2500 nm) using an improved calibrated and validated reflectance technique and applied to urban aerosol samples from Sao Paulo, Brazil and from a site in Virginia, Eastern US, that experiences transported urban/industrial aerosol. The average alpha (sub a) values (approximately 3 square meters per gram at 550 nm) for Sao Paulo samples are 10 times larger than alpha (sub a) values obtained for aerosols in Virginia. Sao Paulo aerosols also show evidence of enhanced UV absorption in selected samples, probably associated with organic aerosol components. This extra UV absorption can double the absorption efficiency observed from black carbon alone, therefore reducing by up to 50% the surface UV fluxes, with important implications for climate, UV photolysis rates, and remote sensing from space.

Martins, J. Vanderlei↗
NASA NTRS1988

The spectral properties of collected interplanetary dust particles

The observed spectral and mineralogical properties of interplanetary dust particles (IDP) allows the conclusion that: (1) the majority of IDP infrared spectra are dominated by olivine, pyroxene, or layer lattice silicate minerals, (2) to the first order the emission spectra of comets Halley and Kohoutek can be matched by mixtures of these IDP infrared types, implying that comets contain mixtures of these different crystalline silicates and may vary from comet to comet and perhaps even within a single comet, (3) do not expect to observe a single 20 micron feature in cometary spectra, (4) carbonaceous materials dominate the visible spectra properties of the IDPs even though the mass in these particles consists primarily of silicates, and (5) the particle characteristics summarized need to be properly accounted for in future cometary emission models.

Sandford, S. A.↗
NASA NTRS2013

Aerosol Airmass Type Mapping Over the Urban Mexico City Region From Space-based Multi-angle Imaging

Using Multi-angle Imaging SpectroRadiometer (MISR) and sub-orbital measurements from the 2006 INTEX-B/MILAGRO field campaign, in this study we explore MISR's ability to map different aerosol air mass types over the Mexico City metropolitan area. The aerosol air mass distinctions are based on shape, size and single scattering albedo retrievals from the MISR Research Aerosol Retrieval algorithm. In this region, the research algorithm identifies dust-dominated aerosol mixtures based on non-spherical particle shape, whereas spherical biomass burning and urban pollution particles are distinguished by particle size. Two distinct aerosol air mass types based on retrieved particle microphysical properties, and four spatially distributed aerosol air masses, are identified in the MISR data on 6 March 2006. The aerosol air mass type identification results are supported by coincident, airborne high-spectral-resolution lidar (HSRL) measurements. Aerosol optical depth (AOD) gradients are also consistent between the MISR and sub-orbital measurements, but particles having single-scattering albedo of approx. 0.7 at 558 nm must be included in the retrieval algorithm to produce good absolute AOD comparisons over pollution-dominated aerosol air masses. The MISR standard V22 AOD product, at 17.6 km resolution, captures the observed AOD gradients qualitatively, but retrievals at this coarse spatial scale and with limited spherical absorbing particle options underestimate AOD and do not retrieve particle properties adequately over this complex urban region. However, we demonstrate how AOD and aerosol type mapping can be accomplished with MISR data over complex urban regions, provided the retrieval is performed at sufficiently high spatial resolution, and with a rich enough set of aerosol components and mixtures.

aerosol optical depth↗
NASA NTRS2015

Scattering Properties of Heterogeneous Mineral Particles with Absorbing Inclusions

We analyze the results of numerically exact computer modeling of scattering and absorption properties of randomly oriented poly-disperse heterogeneous particles obtained by placing microscopic absorbing grains randomly on the surfaces of much larger spherical mineral hosts or by imbedding them randomly inside the hosts. These computations are paralleled by those for heterogeneous particles obtained by fully encapsulating fractal-like absorbing clusters in the mineral hosts. All computations are performed using the superposition T-matrix method. In the case of randomly distributed inclusions, the results are compared with the outcome of Lorenz-Mie computations for an external mixture of the mineral hosts and absorbing grains. We conclude that internal aggregation can affect strongly both the integral radiometric and differential scattering characteristics of the heterogeneous particle mixtures.

minerals↗