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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Comparison of Filter-based Absorption Measurements of Biomass Burning Aerosol and Background Aerosol at the Mt. Bachelor Observatory

In this study we evaluate the recently upgraded aethalometer (AE33) and the newly released tricolor absorption photometer (TAP) with respect to their response to wildfire aerosol plumes during their deployment at the Mount Bachelor Observatory (MBO; 2763 m a.s.l.) in central Oregon, USA, during the summer of 2016. While both instruments use similar methodology (i.e., light extinction through an aerosol-laden filter), each has a unique set of correction schemes to address artifacts originating from filter loading, scattering from captured aerosol particles, and multiple scattering effects of the filter fibers. We also utilize a Single Particle Soot Photometer (SP2) to determine refractory black carbon (rBC) in these air masses. In addition to comparing the AE33 filter-loading correction methodology to previously published aethalometer correction schemes, we also compare the AE33 to the correction schemes used for the TAP and evaluate the degree to which the different correction factors influence the derived absorption Ångström exponents (AAE) and mass absorption cross sections (MACs). We find that while the different correction factors for either the AE33 or TAP do exert an influence on the derived MACs, AAEs exhibit the most sensitivity to the correction schemes. Our study finds that using the AE33 manufacturer’s recommended settings results in aerosol light absorption coefficients that are 3.4 to 4 times greater than the aerosol light absorption coefficients reported by the TAP. We calculated a correction factor (Cf) of 4.35 for the AE33 by normalizing the AE33 to match the TAP. The uncorrected AE33 also gives equivalent black carbon (eBC) values that are approximately 2 times the rBC measured by the SP2 instrument. We also find that biomass burning aerosols result in significant MAC enhancements, particularly at lower wavelengths, which is attributable to brown carbon (BrC).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1974

High purity silica reflective heat shield development

Measurements were made of reflectance in the vacuum ultraviolet down to 0.15 micron. Scattering coefficients (S) and absorption coefficients (K) were also measured. These coefficients express the optical properties and are used directly in a thermodynamic analysis for sizing a heat shield. The effect of the thin silica melt layer formed during entry was also studied from the standpoint of trapped radiant energy.

Blome, J. C.↗
NASA NTRS1981

Absorption of visible radiation by aerosols in the volcanic plume of Mount St. Helens

Samples of particles from Mount St. Helens were collected in both the stratosphere and troposphere for measurement of the light absorption coefficient. Results indicate that the stratospheric dust had a small but finite absorption coefficient ranging up to 2 x 10 to the minus 7 per meter at a wavelength of 0.55 micron, which is estimated to yield an albedo for single scatter of 0.98 or greater. Tropospheric results showed similar high values of an albedo for single scatter

Ogren, J. A.↗
NASA NTRS1986

Rotational collisional narrowing in an infrared CO2 Q branch studied with a tunable-diode laser

A tunable diode laser has been used to observe rotational collisional narrowing or line mixing in the IR absorption spectrum of the Q branch of the (1 1 exp-1 0,0 3 exp-1 0) sub II - 0 0 exp-0 0 band of CO2 at 1932.47/cm over the 100-745 Torr pressure range. The observed absorption coefficients below the band origin are up to 80 percent lower than those calculated on the basis of an isolated Lorentz line approxmation. A simple fitting law is derived for the state-to-state, rotationally inelastic rate constants, on the basis of the known line broadening coefficients; a calculation of the mixing using these rates agrees with observed absorption coefficients to within several percent.

Strow, L. L.↗
NASA NTRS1990

Intersubband absorption in Si(1-x)Ge(x/Si superlattices for long wavelength infrared detectors

Researchers calculated the absorption strengths for intersubband transitions in n-type Si(1-x)Ge(x)/Si superlattices. These transitions can be used for the detection of long-wavelength infrared radiation. A significant advantage in Si(1-x)Ge(x)/Si supperlattice detectors is the ability to detect normally incident light; in Ga(1-x)Al(x)As/GaAs superlattices, intersubband absorption is possible only if the incident light contains a polarization component in the growth direction of the superlattice. Researchers present detailed calculation of absorption coefficients, and peak absorption wavelengths for (100), (111) and (110) Si(1-x)Ge(x)/Si superlattices. Peak absorption strengths of about 2000 to 6000 cm(exp -1) were obtained for typical sheet doping concentrations (approx. equals 10(exp 12)cm(exp -2)). Absorption comparable to that in Ga(1-x)Al(x)As/GaAs superlattice detectors, compatibility with existing Si technology, and the ability to detect normally incident light make these devices promising for future applications.

Rajakarunanayake, Yasantha↗
DOE OSTI2016

Enhancement of acoustical performance of hollow tube sound absorber

This paper presents acoustical performance of hollow structures utilizing the recycled lollipop sticks as acoustic absorbers. The hollow cross section of the structures is arranged facing the sound incidence. The effects of different length of the sticks and air gap on the acoustical performance are studied. The absorption coefficient was measured using impedance tube method. Here it is found that improvement on the sound absorption performance is achieved by introducing natural kapok fiber inserted into the void between the hollow structures. Results reveal that by inserting the kapok fibers, both the absorption bandwidth and the absorption coefficient increase. For test sample backed by a rigid surface, best performance of sound absorption is obtained for fibers inserted at the front and back sides of the absorber. And for the case of test sample with air gap, this is achieved for fibers introduced only at the back side of the absorber.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1973

Polarizability calculations on water, hydrogen, oxygen, and carbon dioxide

A semiclassical model of damped oscillators is used as a basis for the calculation of the dispersion of the refractive index, polarizability, and dielectric permeability in water, hydrogen, and oxygen in liquid and gaseous states, and in gaseous carbon dioxide. The absorption coefficient and the imaginary part of the refractive index are also calculated at corresponding wavelengths. A good agreement is obtained between the observed and calculated values of refractive indices, and between those of absorption coefficients in the region of absorption bands. The calculated values of oscillator strengths and damping factors are also discussed. The value of the polarizability of liquid water was about 2.8 times that of previous calculations.

Nir, S.↗
NASA NTRS1984

Wavenumber dependent investigation of the terrestrial infrared radiation budget with two versions of the LOWTRAN5 band model

Two versions of the LOWTRAN5 radiance code are used in a study of the earth's clear sky infrared radiation budget in the interval 30 per cm (333.3 microns) to 3530 per cm (2.8 microns). One version uses 5 per cm resolution and temperature dependent molecular absorption coefficients, and the second uses 20 per cm resolution and temperature independent molecular absorption coefficients. Both versions compare well with Nimbus 3 IRIS spectra, with some discrepancies at particular wavenumber intervals. Up and downgoing fluxes, calculated as functions of latitude, are displayed for wavenumbers at which the principle absorbers are active. Most of the variation of the fluxes with latitude is found in the higher wavenumber intervals for both clear and cloudy skies. The main features of the wavenumber integrated cooling rates are explained with reference to calculations in more restricted wavenumber intervals. A tropical lower tropospheric cooling maximum is produced by water vapor continuum effects in the 760-1240 per cm window. A secondary upper tropospheric cooling maximum, with wide meridional extent, is produced by water vapor rotational lines between 30-430 per cm. Water vapor lines throughout the terrestrial infrared spectrum prevent the upflux maximum from coinciding with the surface temperature maximum.

Charlock, T. P.↗
NASA NTRS2004

High Spectral Resolution MODIS Algorithms for Ocean Chlorophyll in Case II Waters

The Case 2 chlorophyll a algorithm is based on a semi-analytical, bio-optical model of remote sensing reflectance, R(sub rs)(lambda), where R(sub rs)(lambda) is defined as the water-leaving radiance, L(sub w)(lambda), divided by the downwelling irradiance just above the sea surface, E(sub d)(lambda,0(+)). The R(sub rs)(lambda) model (Section 3) has two free variables, the absorption coefficient due to phytoplankton at 675 nm, a(sub phi)(675), and the absorption coefficient due to colored dissolved organic matter (CDOM) or gelbstoff at 400 nm, a(sub g)(400). The R(rs) model has several parameters that are fixed or can be specified based on the region and season of the MODIS scene. These control the spectral shapes of the optical constituents of the model. R(sub rs)(lambda(sub i)) values from the MODIS data processing system are placed into the model, the model is inverted, and a(sub phi)(675), a(sub g)(400) (MOD24), and chlorophyll a (MOD21, Chlor_a_3) are computed. Algorithm development is initially focused on tropical, subtropical, and summer temperate environments, and the model is parameterized in Section 4 for three different bio-optical domains: (1) high ratios of photoprotective pigments to chlorophyll and low self-shading, which for brevity, we designate as 'unpackaged'; (2) low ratios and high self-shading, which we designate as 'packaged'; and (3) a transitional or global-average type. These domains can be identified from space by comparing sea-surface temperature to nitrogen-depletion temperatures for each domain (Section 5). Algorithm errors of more than 45% are reduced to errors of less than 30% with this approach, with the greatest effect occurring at the eastern and polar boundaries of the basins. Section 6 provides an expansion of bio-optical domains into high-latitude waters. The 'fully packaged' pigment domain is introduced in this section along with a revised strategy for implementing these variable packaging domains. Chlor_a_3 values derived semi-analytically and Chlor_a_2 values derived empirically using the O Reilly et al. OC3M algorithm from MODIS Terra radiances are compared to field chlorophyll-a concentrations in Sections 7 and 8.

Carder, Kendall L.↗
DOE OSTI2019

Obtaining the complex optical constants n and k via quantitative absorption measurements in KBr pellets

Reflectance (emittance) spectroscopy, especially at infrared wavelengths, continues to grow in utility as an analytical technique for contact, standoff, and remote sensing. The reflectance spectra of solids, however, are complex, depending on many parameters, even for the same material. Granule or powder particle size, crystal morphology, layer thickness, and substrate material all affect the spectral distribution of reflected light. However, such phenomena can all be modeled if the optical constants n(?) and k(?) are available. If the quantitative absorption coefficient K(?) is known, the k value can be obtained via the relation k(?) = 2.303K(?)/4p?. The absorption coefficient can in turn be derived from a simple KBr-pellet infrared absorption measurement, provided the pellet mass ratio is prepared quantitatively. The method requires the pellet’s mass and diameter, along with the analyte mass fraction and density. In this paper we demonstrate the requisite experimental details in preparing the pellets, as well as methods to reduce light scattering in order to obtain more quantitative values. Theoretical methods to derive the related optical constants will also be detailed, in particular the assumptions used to obtain the scalar refractive index n. Ideally, this value is known or measured separately, but in some cases we have found that it can be approximated (first approximation) for most organic chemicals by n~1.5 at the shortest wavelength. The results are presented for a couple of species.

optical constants, solids, KBr pellet↗
NASA NTRS1993

The absorption of p-modes by sunspots - Variations with degree and order

A spherical harmonic decomposition of the p-modes into inward and outward propagating waves is employed to investigate the absorption of solar p-modes by an isolated sunspot. The absorption coefficient (averaged over frequency and azimuthal order) is found to increase with increasing horizontal wavenumber k over the range 0-0.8/Mm. For larger horizontal wavenumbers, in the range 0.8-1.5/Mm, the absorption coefficient decreases with increasing k. The absorption along each individual p-mode ridge tends to peak at an intermediate value of the spherical harmonic degree in the range 200-400. The highest absorption is found along the p(1) ridge, and the absorption decreases with increasing radial order.

Bogdan, Thomas J.↗
NASA NTRS1974

Absorption of infrared radiation by electrons in the field of a neutral hydrogen atom

An analytical expression for the absorption coefficient is developed from a relationship between the cross-section for inverse bremsstrahlung absorption and the cross-section for electron-atom momentum transfer; it is accurate for those photon frequencies v and temperatures such that hv/kT is small. The determination of the absorption of infrared radiation by free-free transitions of the negative hydrogen ion has been extended to higher temperatures. A simple analytical expression for the absorption coefficient has been derived.

Stallcop, J. R.↗
DOE OSTI2018

The Ascension Island boundary layer in the remote southeast Atlantic is often smoky

Observations from June through October, 2016, from a surface-based ARM Mobile Facility deployment on Ascension Island (8°S, 14.5°W) indicate that refractory black carbon (rBC) is almost always present within the boundary layer. rBC mass concentrations, light absorption coefficients, and cloud condensation nuclei concentrations vary in concert and synoptically, peaking in August. Light absorption coefficients at three visible wavelengths as a function of rBC mass indirectly indicate the presence of other light-absorbing aerosols (e.g., brown carbon), most pronounced in June. The single-scattering-albedo increases systematically from August to October in both 2016 and 2017, with monthly-means of 0.78±0.02 (August), 0.81±0.03 (September) and 0.83±0.03 (October) at the green wavelength. Boundary-layer aerosol loadings are only loosely correlated with total aerosol optical depth, with smoke more likely to be present in the boundary layer earlier in the biomass-burning season, evolving to smoke predominantly present above the cloud layers in September-October, typically resting upon the cloud-top inversion. The time period with the campaign-maximum near-surface light absorption and column aerosol optical depth, on 13-16 August of 2016, is investigated further. Also, backtrajectories indicate more direct boundary layer transport westward from the African continent is central to explaining the elevated surface aerosol loadings.

47 OTHER INSTRUMENTATION↗
NASA NTRS1986

Laboratory measurements of microwave absorption from gaseous atmospheric constituents under conditions for the outer planets

Quite often the interpretive work on the microwave and millimeter-wave absorption profiles, which are inferred from radio occultation measurements or radio astronomical observations of the outer planets, employs theoretically-derived absorption coefficients to account for contributions to the observed opacity from gaseous constituents. Variations of the actual absorption coefficients from those which are theoretically derived, especially under the environmental conditions characteristic of the outer planets, can result in significant errors in the inferred abundances of the absorbing constituents. The recognition of the need to make laboratory measurements of the absorptivity of gases such as NH3, CH4, and H2O in a predominantly H2 atmosphere, under temperature and pressure conditions simulating the outer planets' atmospheres, and at wavelengths corresponding to both radio occultation and radio astronomical observations, has led to the development of a facility capable of making such measurements at Georgia Tech. The laboratory measurement system, the measurement techniques, and the proposed experimental regimen for Winter 1985 are described.

Steffes, Paul G.↗
DOE OSTI2016

Spectroscopic ellipsometry-based study of optical properties of amorphous and crystalline ZnSnO alloys and Zn{sub 2}SnO{sub 4} thin films grown using sputtering deposition: Dielectric function and subgap states

We investigated the optical properties of amorphous and crystalline zinc tin oxide (ZTO) thin films grown on SiO{sub 2}/Si substrates with varying compositions via a co-sputtering deposition method at room temperature. The co-sputtering targets consist of SnO{sub 2} and ZnO. By varying the relative power ratio of the two targets, we demonstrate the ability to control the Sn and Zn composition of the resulting ZTO thin films. The ratio of [Sn]/([Sn] + [Zn]) atomic compositions was estimated at 11%, 29%, 42%, 54%, and 60%. Using a 600 °C annealing process, the as-grown amorphous ZTO films were transformed into crystalline ZTO films. The dielectric functions were obtained based on the measured ellipsometric angles, ψ and Δ. We determined the dielectric functions, absorption coefficients, and optical gap energies of ZTO thin films with varying compositions. The dielectric functions, absorption coefficients, and optical gap energies of amorphous and crystalline Zn{sub 2}SnO{sub 4} thin films were obtained at 29 at. % of Sn. Subgap states at 1.6 eV (A) and 2.8 eV (B) of ZnSnO alloys and Zn{sub 2}SnO{sub 4} films were found in the imaginary part of the dielectric function spectra. The subgap state intensities were reduced via a nitrogen gas annealing. Possible origins of the observed subgap states will be discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Understanding the optical properties of ZnO{sub 1−x}S{sub x} and ZnO{sub 1−x}Se{sub x} alloys

ZnO{sub 1−x}Y{sub x} with chalcogen element Y exhibits intriguing optoelectronic properties as the alloying strongly impacts the band-gap energy E{sub g}(x). In this work, we analyze and compare the electronic structures and the dielectric responses of Zn(O,S) and Zn(O,Se) alloys by means of the density functional theory and the partially self-consistent GW approach. We model the crystalline stability from the total energies, and the results indicate that Zn(O,S) is more stable as alloy than Zn(O,Se). We demonstrate also that ion relaxation strongly affects total energies, and that the band-gap bowing depends primarily on local relaxation of the bonds. Moreover, we show that the composition dependent band-gap needs to be analyzed by the band anti-crossing model for small alloying concentration, while the alloying band-bowing model is accurate for strong alloying. We find that the Se-based alloys have a stronger change in the band-gap energy (for instance, ΔE{sub g}(0.50) = E{sub g}(ZnO) – E{sub g}(x = 0.50) ≈ 2.2 eV) compared with that of the S-based alloy (ΔE{sub g}(0.50) = 1.2 eV), mainly due to a stronger relaxation of the Zn–anion bonds that affects the electronic structure near the band edges. The optical properties of the alloys are discussed in terms of the complex dielectric function ε(ω) = ε{sub 1}(ω) + iε{sub 2}(ω) and the absorption coefficient α(ω). While the large band-gap bowing directly impacts the low-energy absorption spectra, the high-frequency dielectric constant ε{sub ∞} is correlated to the intensity of the dielectric response at energies above 4 eV. Therefore, the dielectric constant is only weakly affected by the non-linear band-gap variation. Despite strong structural relaxation, the high absorption coefficients of the alloys demonstrate that the alloys have well-behaved optoelectronic properties.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1980

Laser-heated thruster

The development of a computer program for the design of the thrust chamber for a CW laser heated thruster was examined. Hydrodgen was employed as the propellant gas and high temperature absorber. The laser absorption coefficient of the mixture/laser radiation combination is given in temperature and species densities. Radiative and absorptive properties are given to determine radiation from such gas mixtures. A computer code for calculating the axisymmetric channel flow of a gas mixture in chemical equilibrium, and laser energy absorption and convective and radiative heating is described. It is concluded that: (1) small amounts of cesium seed substantially increase the absorption coefficient of hydrogen; (2) cesium is a strong radiator and contributes greatly to radiation of cesium seeded hydrogen; (3) water vapor is a poor absorber; and (4) for 5.3mcm radiation, both H2O/CO and NO/CO seeded hydrogen mixtures are good absorbers.

Kemp, N. H.↗