SEARCH · Engineering Papers

Results for “Spectral shape”

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 991 records · Page 55

All sources NASA NTRS DOE OSTI

NASA NTRS1993

ROSAT observations of pulsed soft X-ray emission from PSR 1055-52

Utilizing the position-sensitive proportional counter and the high-resolution imager aboard the orbiting X-ray observatory ROSAT, we have detected pulsations at the radio period from the pulsar PSR 1055-52. The pulse shapes are energy-dependent and show a transition at about 0.5 keV where the phase angle of the pulse peak changes by about -120 deg and the pulsed fraction increases from 11 percent to 63 percent toward larger energies. Simple spectral models are found to be unsatisfactory, while multicomponent models, such as a soft blackbody and hard power-law tail, yield better fits to the pulse-height data. The hard power-law tail is consistent with the extension of the recently reported EGRET results and may indicate a common emission mechanism for the X-ray through GeV gamma-ray regime. The soft blackbody component with T(infinity) = (7.5 +/- 0.6) x 10 exp 5 K, if interpreted as the initial cooling of a neutron star, is consistent with standard cooling models and does not require the presence of exotic components.

Oegelman, Hakki↗

NASA NTRS1994

Laser/lidar analysis and testing

Section 1 of this report details development of a model of the output pulse frequency spectrum of a pulsed transversely excited (TE) CO2 laser. In order to limit the computation time required, the model was designed around a generic laser pulse shape model. The use of such a procedure allows many possible laser configurations to be examined. The output pulse shape is combined with the calculated frequency chirp to produce the electric field of the output pulse which is then computationally mixed with a local oscillator field to produce the heterodyne beat signal that would fall on a detector. The power spectral density of this heterodyne signal is then calculated. Section 2 reports on a visit to the LAWS laser contractors to measure the performance of the laser breadboards. The intention was to acquire data using a digital oscilloscope so that it could be analyzed. Section 3 reports on a model developed to assess the power requirements of a 5J LAWS instrument on a Spot MKII platform in a polar orbit. The performance was assessed for three different latitude dependent sampling strategies.

Spiers, Gary D.↗

NASA NTRS2017

Osiris-REx Spacecraft Current Status and Forward Plans

The NASA New Frontiers OSIRIS-REx spacecraft executed a flawless launch on September 8, 2016 to begin its 23-month journey to near-Earth asteroid (101955). The primary objective of the OSIRIS-REx mission is to collect and return to Earth a pristine sample of regolith from the asteroid surface. The sampling event will occur after a two-year period of remote sensing that will ensure a high probability of successful sampling of a region on the asteroid surface having high science value and within well-defined geological context. The OSIRIS-REx instrument payload includes three high-resolution cameras (OCAMS), a visible and near-infrared spectrometer (OVIRS), a thermal imaging spectrometer (OTES), an X-ray imaging spectrometer (REXIS), and a laser altimeter (OLA). As the spacecraft follows its nominal outbound-cruise trajectory, the propulsion, power, communications, and science instruments have undergone basic functional tests, with no major issues. Outbound cruise science investigations include a search for Earth Trojan asteroids as the spacecraft approaches the Sun-Earth L4 Lagrangian point in February 2017. Additional instrument checkouts and calibrations will be carried out during the Earth gravity assist maneuver in September 2017. During the Earth-moon flyby, visual and spectral images will be acquired to validate instrument command sequences planned for Bennu remote sensing. The asteroid Bennu remote sensing campaign will yield high resolution maps of the temperature and thermal inertia, distributions of major minerals and concentrations of organic matter across the asteroid surface. A high resolution 3d shape model including local surface slopes and a high-resolution gravity field will also be determined. Together, these data will be used to generate four separate maps that will be used to select the sampling site(s). The Safety map will identify hazardous and safe operational regions on the asteroid surface. The Deliverability map will quantify the accuracy with which the navigation team can deliver the spacecraft to and from specific sites on the asteroid surface. The Sampleability map quantifies the regolith properties, providing an estimation of how much material would be sampled at different points on the surface. The final Science Value map synthesizes the chemical, mineralogical, and geological, observations to identify the areas of the asteroid surface with the highest science value. Here, priority is given to organic, water-rich regions that have been minimally altered by surface processes. Asteroid surface samples will be acquired with a touch-and-go sample acquisition system (TAGSAM) that uses high purity pressurized N2 gas to mobilize regolith into a stainless steel canister. Although the mission requirement is to collect at least 60 g of material, tests of the TAGSAM routinely exceeded 300 g of simulant in micro-gravity tests. After acquiring the sample, the spacecraft will depart Bennu in 2021 to begin its return journey, with the sample return capsule landing at the Utah Test and Training Range on September 23, 2023. The OSIRIS-REx science team will carry out a series of detailed chemical, mineralogical, isotopic, and spectral studies that will be used to determine the origin and history of Bennu and to relate high spatial resolution sample studies to the global geological context from remote sensing. The outline of the sample analysis plan is described in a companion abstract.

Messenger, Scott↗

NASA NTRS1999

Spectral Behavior of Hematite at Visible/Near Infrared and Midinfrared Wavelengths

The oxide mineral hematite alpha-Fe2O3) is present on Mars as evidenced by spectroscopy using visible/near infrared (VNIR) and midinfrared (MIR) wavelengths. The physical nature of this surficial hematite varies from fine-grained, crystalline red hematite (red-Hm) in certain martian bright regions, to coarser-grained, crystalline gray hematite (gray-Hm) in the Sinus Meridiani equatorial site discovered in the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) data. The VNIR spectra require that the red hematite is present in amounts subordinate to a second ferric pigment, which accounts for the general shape and position of the martian ferric absorption edge. By analogy with palagonitic tephra and synthetic samples, the pigment is a nanophase ferric oxide, possibly nanophase hematite (np-Hm). The purpose of this abstract is to document the physicospectral properties of hematite in the VNIR (0.35 to 2.2 microns) and MIR (5 to 25 microns) with respect to the terms "nanophase" and "crystalline", "red" and "gray", and "fine-grained" and "coarse-grained". We will show that different "types" of hematite (no-, red-, and gray-Hm) have different spectral responses in the VNIR and MIR regions and that these differences are important for inferring the types of hematite and their relative proportions from remotely sensed spectra of Mars. Because hematite is an alteration product that forms through many different geologic processes, determination of the type of hematite provides important clues about the style and diversity of martian weathering processes.

Lane, Melissa D.↗

NASA NTRS1999

Spectral Behavior of Hematite at Visible/Near Infrared and Midinfrared Wavelengths

The oxide mineral hematite alpha-Fe2O3) is present on Mars as evidenced by spectroscopy using visible/near infrared (VNIR) and midinfrared (MIR) wavelengths. The physical nature of this surficial hematite varies from fine-grained, crystalline red hematite (red-Hm) in certain martian bright regions, to coarser-grained, crystalline gray hematite (gray-Hm) in the Sinus Meridiani equatorial site discovered in the Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) data. The VNIR spectra require that the red hematite is present in amounts subordinate to a second ferric pigment, which accounts for the general shape and position of the martian ferric absorption edge. By analogy with palagonitic tephra and synthetic samples, the pigment is a nanophase ferric oxide, possibly nanophase hematite (np-Hm). The purpose of this abstract is to document the physicospectral properties of hematite in the VNIR (0.35 to 2.2 mm) and MIR (5 to 25 mm) with respect to the terms "nanophase" and "crystalline", "red" and "gray", and "fine-grained" and "coarse-grained". We will show that different "types" of hematite (np-, red-, and gray-Hm) have different spectral responses in the VNIR and MIR regions and that these differences are important for inferring the types of hematite and their relative proportions from remotely sensed spectra of Mars. Because hematite is an alteration product that forms through many different geologic processes, determination of the type of hematite provides important clues about the style and diversity of martian weathering processes. Additional information is contained in the original extended abstract.

Lane, M. D.↗

NASA NTRS1981

Extremely red compact radio sources - The empty field objects

Radiation of 10 microns has been detected from 1413+135, one of the very red objects discovered by Rieke, Lebofsky, and Kinman (1979) at near-infrared wavelengths. The spectrum of this object flattens at wavelengths longer than 2.2 microns. Upper limits are also given for the 10-micron emission from 2255+14, 0026+34, and 0406+121. Photometry between 1.25 and 2.2 microns confirms the variability of 1413+135, 2255+41, and 0406+121. Five percent resolution spectra of 1413+135 and 0406+121 between 1.5 and 2.4 microns show no emission or absorption lines. The spectral data rule out the possibility that 1413+135 is a quasar with normal line strengths and a redshift less than 1.3 and greater than 4. The lack of features of the 1.5-2.4-micron spectra, the rapid variability, and the overall shape of the radio, infrared, and X-ray energy distributions are consistent with a BL Lac nature for these objects.

Beichman, C. A.↗

NASA NTRS1989

Physically-based parameterization of spatially variable soil and vegetation using satellite multispectral data

A stochastic-geometric landsurface reflectance model is formulated and tested for the parameterization of spatially variable vegetation and soil at subpixel scales using satellite multispectral images without ground truth. Landscapes are conceptualized as 3-D Lambertian reflecting surfaces consisting of plant canopies, represented by solid geometric figures, superposed on a flat soil background. A computer simulation program is developed to investigate image characteristics at various spatial aggregations representative of satellite observational scales, or pixels. The evolution of the shape and structure of the red-infrared space, or scattergram, of typical semivegetated scenes is investigated by sequentially introducing model variables into the simulation. The analytical moments of the total pixel reflectance, including the mean, variance, spatial covariance, and cross-spectral covariance, are derived in terms of the moments of the individual fractional cover and reflectance components. The moments are applied to the solution of the inverse problem: The estimation of subpixel landscape properties on a pixel-by-pixel basis, given only one multispectral image and limited assumptions on the structure of the landscape. The landsurface reflectance model and inversion technique are tested using actual aerial radiometric data collected over regularly spaced pecan trees, and using both aerial and LANDSAT Thematic Mapper data obtained over discontinuous, randomly spaced conifer canopies in a natural forested watershed. Different amounts of solar backscattered diffuse radiation are assumed and the sensitivity of the estimated landsurface parameters to those amounts is examined.

Jasinski, Michael F.↗

NASA NTRS1992

Mapping Mars water vapor with the Very Large Array

This paper presents the first radio measurements of Mars atmospheric water, retrieved from interferometric spectral line observations with the NRAO VLA. Large atmospheric path lengths on the limb of Mars lead to an annulus of H2O line emission which provides a measure of the diurnal and latitudinal variability of atmospheric water on Mars. The measured line shapes of the observed H2O emission yield the first direct measurements of the vertical mixing profile of H2O in the Mars atmosphere. The observations indicate a very dry Mars atmosphere in which the globally averaged water column is approximately 3 pr micron.

Clancy, R. T.↗

NASA NTRS2002

Cometary Silicates: Interstellar and Nebular Materials

Evidence for interstellar material in comets is deduced from IR spectra, insitu measurements of Halley, and chondritic porous interplanetary dust particles (CP IDPs). IR spectra of comets reveal the spectrally active minerals: amorphous carbon, amorphous silicates, and (in some comets) crystalline silicates. Evidence suggests amorphous silicates are of interstellar origin while crystalline silicates are of nebular origin. 10 microns spectra of comets and submicron amorphous silicate spherules in CP IDPs have shapes similar to lines-of-sight through the ISM. Thermal emission models of cometary IR spectra require Fe-bearing amorphous silicates. Fe-bearing amorphous silicates may be Fe-bearing crystalline silicates formed in AGB outflows that are amorphized through He+ ion bombardment in supernova shocks in the ISM. Crystalline silicates in comets, as revealed by IR spectra, and their apparent absence in the ISM, argues for their nebular origin. The high temperatures (less than l000 K) at which crystals form or are annealed occur in the inner nebula or in nebular shocks in the 5-10 AU region. Oxygen isotope studies of CP IDPs show by mass only 1 % of the silicate crystals are of AGB origin. Together this suggests crystalline silicates in comets are probably primitive grains from the early solar nebula.

Wooden, Diane H.↗

NASA NTRS2004

Dust aerosol retrieval results from MISR (multi-angle imaging spectro-radiometer)

Satellite measurements provide important tools for understanding the effect of mineral dust aerosols on past and present climate and climate predictions. Multi-angle instruments such as Multi-angle Imaging Spectro- Radiometer (MISR) provide independent constraints on aerosol properties based on their sensitivity to the shape of aerosol scattering phase functions. The current MISR operational retrieval algorithm (version 16 and higher) was modified by incorporating new non-spherical dust models that account for naturally occurring dust shapes and compositions. We present selected examples of MISR version 16 retrievals over AERONET sunphotometer land and ocean sites during the passage of dust fronts. Our analysis shows that during such events MISR retrieves Angstrom exponents characteristic of large particles, having little spectral variation in extinction over the MISR wavelength range (442, 550, 672 and 866 nm channels), as expected. The retrieved fraction of non-spherical particles is also very high. This quantity is not retrieved by satellite instruments having only nadir-viewing cameras. Our comparison of current (version 16) MISR-retrieved aerosol optical thickness (AOT) with AERONET instantaneous AOT shows better coverage and stronger correlations than when making identical comparisons with previous AOT retrievals (version 15). The MISR algorithm successful mixtures include a non-spherical dust component with high frequency in retrievals over dark water and slightly lower frequency over land. Selection frequencies of non-spherical dust models also decrease in dusty regions affected by pollution.

Multiangle Imaging Spectroradiometer (MISR)↗

NASA NTRS2017

Synthetic Absorption Lines for a Clumpy Medium: A Spectral Signature for Cloud Acceleration in AGN?

There is increasing evidence that the highly ionized multiphase components of AGN disc winds may be due to thermal instability. The ions responsible for forming the observed X-ray absorption lines may only exist in relatively cool clumps that can be identified with the so-called warm absorbers. Here we calculate synthetic absorption lines for such warm absorbers from first principles by combining 2D hydrodynamic solutions of a two-phase medium with a dense grid of photoionization models to determine the detailed ionization structure of the gas. Our calculations reveal that cloud disruption, which leads to a highly complicated velocity field (i.e. a clumpy flow), will only mildly affect line shapes and strengths when the warm gas becomes highly mixed but not depleted. Prior to complete disruption, clouds that are optically thin to the driving UV resonance lines will cause absorption at an increasingly blueshifted line-of-sight velocity as they are accelerated. This behavior will imprint an identifiable signature on the line profile if warm absorbers are enshrouded in an even broader absorption line produced by a high column of intercloud gas. Interestingly, we show that it is possible to develop a spectral diagnostic for cloud acceleration by differencing the absorption components of a doublet line, a result that can be qualitatively understood using a simple partial covering model. Our calculations also permit us to comment on the spectral differences between cloud disruption and ionization changes driven by flux variability. Notably, cloud disruption offers another possibility for explaining absorption line variability.

line: formation â€“ galaxies: nuclei â€“ quasars: ↗

NASA NTRS1972

New theory for giant loops.

Four very large, shell-shaped features are known from the surveys of radio emission from the Galaxy. It is suggested that the giant loops represent a class of nebulae, induced by supernova radiation as opposed to supernova ejecta. The model considered provides a qualitative explanation for the spectral and polarization properties of the radio emission from giant loops. The radio emitting electrons are part of the general cosmic ray gas and need not arise specifically in the supernova that produced the fossil Stroemgren sphere.

Brandt, J. C.↗

NASA NTRS1981

The RS Canum Venaticorum binaries

This review presents a brief up-to-date summary of observational properties of RS CVn binaries, with emphasis on the photometric. A table of the 69 systems known at this time give the orbital period, mean apparent V magnitude, spectral classification, range of amplitude determinations for the photometric wave, and an indication of known period variations and eclipses. Points considered are (1) the underlying cause of the extreme surface activity, (2) the evolutionary status, (3) the geometric configuration, (4) the temperature, size, shape, location, and lifetimes of the dark spot regions, (5) synchronization of rotational and orbital motion, (6) spectroscopic features in the optical and far ultraviolet, (7) the wave migration, (8) the search for spot cycles, and (9) the orbital period variations produced by the enhanced stellar wind.

Hall, D. S.↗

NASA NTRS1983

Radiative properties of advanced spacecraft heat shield materials

Experimental results are presented to show the effects of simulated reentry exposure by convective heating and by radiant heating on spectral and total emittance of statically oxidized Inconel 617 and Haynes HS188 superalloys to 1260 K and a silicide coatea (R512E) columbium 752 alloy to 1590 K. Convective heating exposures were conducted in a supersonic arc plasma wind tunnel using a wedge-shaped specimen configuration. Radiant tests were conducted at a pressure of .003 atmospheres of dry air at a flow velocity of several meters per second. Convective heating specimens were subjected to 8, 20, and 38 15-min heating cycles, and radiant heating specimens were tested for 10, 20, 50, and 100 30-min heating cycles. Changes in radiative properties are explained in terms of changes in composition resulting from simulated reentry tests. The methods used to evaluate morphological, compositional and crystallographic changes include: Auger electron spectroscopy; scanning electron microscopy; X-ray diffraction analysis; and electron microprobe analysis.

Cunnington, G. R.↗

NASA NTRS1985

Theoretical analysis of Wolter/LSM X-ray telescope systems

A ray tracing analysis has been performed for the spectral slicing zoom X-ray telescope for configurations in which a convex layered synthetic microstructure (LSM) optic is placed in front of the prime focus or a concave LSM optic is placed behind the prime focus. The analysis has considered the geometrical shape of the LSM optic to be either a hyperboloid, sphere, ellipsoid or constant optical path aspheric element for two configurations of the glancing incidence X-ray telescope: the ATM Experimental S-056 Wolter I system and the Stanford/MSFC Wolter-Schwarzchild nested system. For the different systems the RMS blur circle radii, the point spread function (PSF), the full width half maximum (FWHM) of the PSF have been evaluated as a function of field angle and magnification of the secondary to determine resolution of the system. The effects of decentration and tilt of the selected LSM element on the performance of the system have been studied to determine mounting and alignment tolerances.

Shealy, D. L.↗

NASA NTRS1992

The polar cap structure of the X-ray pulsar 4U 1538 - 52

We compare the pulse-phase-dependent spectral observations of 4U 1538 - 52 obtained from Ginga to a series of static model atmospheres of curved accreting polar caps, utilizing a magnetized radiative transfer code with relativistic polarized cross sections. A chi-squared fit was performed on the symmetrized pulse shapes, allowing the parameters of the two polar caps to vary independently. We find evidence for a significant difference between the caps, both in terms of opening angle and temperature, while the optical depth is similar and compatible with radiative deceleration models. The polar caps appear larger than what is usually estimated from dipole fields, and are not located at the antipodes of each other. A broader distribution of magnetic fields is required than expected from a dipolar field at constant radius. If the magnetic field is indeed dipolar, it should be off-center in respect to the star and the accretion shock height exhibits an unusual dependence on the polar angle. An alternative possibility is that the magnetic field is disordered on scales small compared to the polar cap radius.

Bulik, T.↗

NASA NTRS1999

Data Processing for the Near Earth Asteroid Rendezvous (NEAR), X-ray and Gamma-ray Spectrometer (XGRS) Ground System

An X-ray and Gamma-ray spectrometer (XGRS) is onboard the Near Earth Asteroid Rendezvous (NEAR) spacecraft to determine the elemental composition of the surface of the asteroid 433Eros. The Eros asteroid is highly non-spherical in physical shape and the development of data management and analysis methodologies are in several areas a divergence from traditional remotely sensed geographical information systems techniques. Field of view and asteroid surface geometry must be derived virtually and then combined with real measurements of solar, spectral and instrument calibration information to derive meaningful scientific results. Spatial resolution of planned geochemical maps will be improved from the initial conditions of low statistical significance per integration by repeated surface flyovers and regional spectral accumulation. This paper describes the results of a collaborative effort of design and development of the NEAR XGRS instrument ground system undertaken by participants at the Goddard Space Flight Center, University of Arizona, Cornell University, Applied Physics Laboratory, and Max Plank institute.

McClanahan, Timothy P.↗

NASA NTRS1999

Data Processing for the Near Earth Asteroid Rendezvous (NEAR), X-Ray and Gamma-Ray Spectrometer (XRS) Ground System

McClanahan, Timothy P.↗