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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Long-slit optical spectroscopy of powerful far-infrared galaxies - The nature of the nuclear energy source

Optical spectroscopic data are presented for a sample of 47 powerful far-IR galaxies chosen for IR spectral shape, and for six other IR-bright galaxies. The stellar absorption lines expected from a population of old stars are generally very weak in the nuclei of the galaxies. Very weak Mg I absorption is found in regions well off the nucleus, implying that the visible spectrum is dominated by young stars and not by an AGN. At least one, and probably five, of the galaxies have detectable WR emission features, providing additional evidence for a young stellar population. About 20 percent of the galaxies have strong Balmer absorption lines, indicating the presence of a substantial intermediate-age stellar population. The equivalent width of the H-alpha emission line can be modeled as arising from a mixture of a large young population and an intermediate-age population of stars.

Armus, Lee↗
NASA NTRS1990

2060 Chiron - Colorimetry and cometary behavior

Ambiguities concerning the fit of the 2060 Chiron's visible spectrum to its IR spectrum have been resolved by resort to VRIJHK colorimetry obtained in 1988, which also confirms the neutrality of Chiron's taxonomic class C spectrum and indicates that Chiron has anomalously brightened since 1980-1983. This brightening, and one reported in 1978, are consistent with the hypothesis that Chiron sporadically undergoes weak cometary outbursts similar to those of comet P/Schwassmann-Wachmann 1; Chiron is further speculated to be an ice-rich object darkened by C-class carbonaceous soil, and may have been scattered from the Oort cloud in recent solar system history.

Hartmann, William K.↗
NASA NTRS1989

Solar sensor subsystems alignment check using solar scans for the Halogen Occultation Experiment

The alignment of a dual-axes sun sensor subsystem to a telescope having a multiple sensor subsystem is described. The sun sensor consists of two analog and one digital silicon detectors. The analog detectors are shadow mask type operating in the visible spectrum. The detectors are mounted for azimuth and elevation positioning of biaxial gimbals. The digital detector is a linear diode array that operates at a spectral position of 0.7 micron and is used for elevation positioning. The position signals correspond to relative angles between the sun sensor and the solar disk. These three detectors are aligned on an Invar structure which is mounted to a Cassegrain telescope. This telescope relays solar radiance to an eight channel detector subsystem operating in the infrared range from 2 to 10 microns. The test technique and results to check the boresight alignment of these two subsystems by scanning the solar disk will be reported. The boresight alignment for both the azimuth and elevation axes of the two detector subsystems is verified using this technique.

Jurczyk, S. G.↗
NASA NTRS1991

Wavelength variation of p-mode intensity fluctuations

The oscillatory signal in the solar p-mode band has been measured as a function of optical wavelength using a grating spectrometer and Fourier transform spectrometer. The relative intensity fluctuations are found to increase with height in the solar photosphere, while the absolute level of intensity fluctuations in the p-mode band is reduced by about 50 percent in the cores and wings of Ca II H and K, H-delta, and H-gamma compared to the neighboring spectral regions. Thus, these spectral regions of diminished absolute p-mode signal could be exploited as signal references by spectrophotometers while attempting to observe nonradial p-mode oscillations in stars from the ground. High spectral and temporal resolution observations of several unblended lines in the red portion of the visible spectrum show an asymmetry in the relative and absolute p-mode intensity oscillations across the line profiles. The peak in intensity oscillations lies in the blue wing of the lines.

Ronan, R. S.↗
NASA NTRS1992

Video System Highlights Hydrogen Fires

Video system combines images from visible spectrum and from three bands in infrared spectrum to produce color-coded display in which hydrogen fires distinguished from other sources of heat. Includes linear array of 64 discrete lead selenide mid-infrared detectors operating at room temperature. Images overlaid on black and white image of same scene from standard commercial video camera. In final image, hydrogen fires appear red; carbon-based fires, blue; and other hot objects, mainly green and combinations of green and red. Where no thermal source present, image remains in black and white. System enables high degree of discrimination between hydrogen flames and other thermal emitters.

Youngquist, Robert C.↗
NASA NTRS1992

Evaluation of high quantum efficiency silicon photodiodes for calibration in the 400 nm to 900 nm spectral region

The reflectance and internal quantum efficiency (QE) of three single-element photodiodes are determined using two different light-trapping devices. The QED-200 light trapping device which is based on inversion layer photodiodes exhibits the best performance within the short wavelengths of the visible spectrum (VIS), while the A-O device based on p-n photodiodes, performs best in the long wave VIS up to 950 nm. The combination of the two light-traps provides nearly 100 percent external QE coverage from 400 to 950 nm. The reflectances and internal QE were determined within this spectral range for three photodiodes: UV100, an inversion layer photodiode; X-UV100, a shallow diffused n-p photodiode; and 10DPI/SB, a blue-enhanced p-n photodiode.

Jorquera, Carlos↗
NASA NTRS1992

Charge-coupled device imaging spectroscopy of Mars. I - Instrumentation and data reduction/analysis procedures

This paper describes the collection, reduction, and analysis of 0.4-1.0-micron Mars imaging spectroscopy data obtained during the 1988 and 1990 oppositions from Mauna Kea Observatory and provides a general outline for the acquisition and analysis of similar imaging spectroscopy data sets. The U.H. 2.24-m Wide Field Grism CCD Spectrograph was used to collect 13 3D image cubes covering 90 percent of the planet south of 50 deg N in the 0.4-0.8 micron region and covering 55 percent of the planet south of 50 deg N in the 0.5-1.0 micron region. Spectra extracted from these image cubes reveal the detailed character of the Martian near-UV to visible spectrum. Images at red wavelengths reveal the 'classical' albedo markings at 100-500 km spatial resolution while images at blue wavelengths show little surface feature contrast and are dominated by condensate clouds/hazes and polar ice.

Bell, James F., III↗
NASA NTRS1993

Crystal growth of ZnSe and related ternary compound semiconductors by physical vapor transport

The materials to be investigated are ZnSe and related ternary semiconducting alloys (e.g., ZnS(x)Se(1-x), ZnTe(x)Se(1-x), and Zn(1-x)Cd(x)Se). These materials are useful for opto-electronic applications such as high efficient light emitting diodes and low power threshold and high temperature lasers in the blue-green region of the visible spectrum. The recent demonstration of its optical bistable properties also makes ZnSe a possible candidate material for digital optical computers. The investigation consists of an extensive ground-based study followed by flight experimentation, and involves both experimental and theoretical work. The objectives of the ground-based work are to establish the characteristics of the crystals grown on Earth as a basis for subsequent comparative evaluations of the crystals grown in a low gravity environment and to obtain the experimental data and perform the analyses required to define the optimum parameters for the flight experiments. During the six months of the Preliminary Definition Phase, the research efforts were concentrated on the binary compound ZnSe - the purification of starting materials of Se by zone refining, the synthesis of ZnSe starting materials, the heat treatments of the starting materials, the vapor transport rate measurements, the vapor partial pressure measurements of ZnSe, the crystal growth of ZnSe by physical vapor transport, and various characterization on the grown ZnSe crystals.

Su, Ching-Hua↗
NASA NTRS1993

Color separation gratings

In this paper, we describe the theory, fabrication and test of a binary optics 'echelon'. The echelon is a grating structure which separates electromagnetic radiation of different wavelengths, but it does so according to diffraction order rather than by dispersion within one diffraction order, as is the case with conventional gratings. A prototype echelon, designed for the visible spectrum, is fabricated using the binary optics process. Tests of the prototype show good agreement with theoretical predictions.

Farn, Michael W.↗
NASA NTRS1993

The solar spectral irradiances from x ray to radio wavelengths

Sources of new measurements of the solar EUV, UV, and visible spectrum are presented together with discussion of formation of the solar spectrum as a problem in stellar atmospheres. Agreement between the data and a modern synthetic spectrum shows that observed radiative variability is a minor perturbation on a photosphere in radiative equilibrium and local thermodynamic equilibrium (LTE). Newly observed solar variability in 1992 defines a magnetic episode on the Sun closely associated with changes in both spectral irradiances and the total irradiance. This episode offers the opportunity to track the relationship between radiation and magnetic flux evolution.

White, O. R.↗
NASA NTRS1994

A model-based approach for detection of runways and other objects in image sequences acquired using an on-board camera

This research was initiated as a part of the Advanced Sensor and Imaging System Technology (ASSIST) program at NASA Langley Research Center. The primary goal of this research is the development of image analysis algorithms for the detection of runways and other objects using an on-board camera. Initial effort was concentrated on images acquired using a passive millimeter wave (PMMW) sensor. The images obtained using PMMW sensors under poor visibility conditions due to atmospheric fog are characterized by very low spatial resolution but good image contrast compared to those images obtained using sensors operating in the visible spectrum. Algorithms developed for analyzing these images using a model of the runway and other objects are described in Part 1 of this report. Experimental verification of these algorithms was limited to a sequence of images simulated from a single frame of PMMW image. Subsequent development and evaluation of algorithms was done using video image sequences. These images have better spatial and temporal resolution compared to PMMW images. Algorithms for reliable recognition of runways and accurate estimation of spatial position of stationary objects on the ground have been developed and evaluated using several image sequences. These algorithms are described in Part 2 of this report. A list of all publications resulting from this work is also included.

Kasturi, Rangachar↗
NASA NTRS1993

Relationships between pigment composition variation and reflectance for plant species from a coastal savannah in California

Advances in imaging spectroscopy have indicated that remotely sensed reflectance measurements of the plant canopy may be used to identify and qualify some classes of canopy biochemicals; however, the manner in which differences in biochemical compositions translate into differences is not well understood. Most frequently, multiple linear regression routines have been used to correlate narrow band reflectance values with measured biochemical concentrations. Although some success has been achieved with such methods for given data sets, the bands selected by multiple regression are not consistent between data sets, nor is it always clear what physical or biological basis underlies the correlation. To examine the relationship between biochemical concentration and leaf reflectance signal we chose to focus on the visible spectrum where the primary biochemical absorbances are due to photosynthetic pigments. Pigments provide a range of absorbance features, occur over a range of concentrations in natural samples, and are ecophysiologically important. Concentrations of chlorophyll, for example, have been strongly correlated to foliar nitrogen levels within a species and to photosynthetic capacity across many species. In addition pigments effectively absorb most of the photosynthetically active radiation between 400-700 nm, a spectral region for which silicon detectors have good signal/noise characteristics. Our strategy has been to sample a variety of naturally occurring species to measure leaf reflectance and pigment compositions. We hope to extend our understanding of pigment reflectance effects to interpret small overlapping absorbances of other biochemicals in the infrared region. For this reason, selected samples were also tested to determine total nitrogen, crude protein, cellulose, and lignin levels. Leaf reflectance spectra measured with AVIRIS bandwidths and wavelengths were compared between species and within species and for differences between seasons, for changes in the the shape of the spectra. We attempt to statistically correlate these shape changes with differences in pigment compositions. In parallel with our comparisons of pigment composition and leaf reflectance, we have modified the PROSPECT leaf reflectance model to test the contributions of pigments or pigment group concentrations. PROSPECT considers a leaf as a multi-layer dielectric plane with an uneven surface. Jacquemoud adapted the basic analysis of Allen for surface effects, a leaf thickness factor, and the absorption of water and chlorophyll (actually all pigments) and the plant matrix. Our modifications to PROSPECT in the forward direction include breaking out the pigment concentration parameter into separate components for chlorophyll a and b and a number of xanthophylls and carotenes, and introducing a shift and convolution function to model the spread and shift from their in vitro measurements to their in vivo state. Further, we have considered how the matrix elements (i.e., all biochemicals and structural effects not modeled explicity) vary with species.

Ustin, Susan L.↗
NASA NTRS1994

Ocular hazards of light

The eye is protected against bright light by the natural aversion response to viewing bright light sources. The aversion response normally protects the eye against injury from viewing bright light sources such as the sun, arc lamps and welding arcs, since this aversion limits the duration of exposure to a fraction of a second (about 0.25 s). The principal retinal hazard resulting from viewing bright light sources is photoretinitis, e.g., solar retinitis with an accompanying scotoma which results from staring at the sun. Solar retinitis was once referred to as 'eclipse blindness' and associated 'retinal burn'. Only in recent years has it become clear that photoretinitis results from a photochemical injury mechanism following exposure of the retina to shorter wavelengths in the visible spectrum, i.e., violet and blue light. Prior to conclusive animal experiments at that time, it was thought to be a thermal injury mechanism. However, it has been shown conclusively that an intense exposure to short-wavelength light (hereafter referred to as 'blue light') can cause retinal injury. The product of the dose-rate and the exposure duration always must result in the same exposure dose (in joules-per-square centimeter at the retina) to produce a threshold injury. Blue-light retinal injury (photoretinitis) can result from viewing either an extremely bright light for a short time, or a less bright light for longer exposure periods. This characteristic of photochemical injury mechanisms is termed reciprocity and helps to distinguish these effects from thermal burns, where heat conduction requires a very intense exposure within seconds to cause a retinal coagulation otherwise, surrounding tissue conducts the heat away from the retinal image. Injury thresholds for acute injury in experimental animals for both corneal and retinal effects have been corroborated for the human eye from accident data. Occupational safety limits for exposure to UVR and bright light are based upon this knowledge. As with any photochemical injury mechanism must consider the action spectrum, which describes the relative effectiveness of different wavelengths in causing a photobiological effect. The action spectrum for photochemical retinal injury peaks at approximately 440 nm.

Sliney, David H.↗
NASA NTRS1998

Fabrication and Atomic Force Microscopy Characterization of Molecular Composites of Fullerenes in Aerogel Matrix for Optical Limiting

An optical limiter is a device which exhibits a decrease in the transmittance in a material with an increase in intensity of light. Sol-gel techniques offer many advantages in the fabrication of materials. These materials possess many desirable properties for nonlinear optical (NLO) device applications which include transparency, high thermal and chemical stabilities, very low refractive index and dielectric constants. C60 shows a higher excited state absorption cross section than the ground state absorption cross section over the complete visible spectrum, and the spectrum of the excited state absorption of C60 has the same general shape as the ground state absorption. This fact suggests that fullerenes are ideal optical limiting materials. Aerogels are fabricated by sol-gel processing. One of the key issues is the dispersion of fullerenes into small and uniform pores of silica aerogel host matrices. The aerogel network was characterized by Raman spectroscopy. Atomic force microscopy is a technique with many advantages to characterize the aerogel materials. The morphology of the cleaved surface for a C60/aerogel sample shows that there are long paralleled shaped stripes with 20-30 nm in width and about 500 nm in length on the cleaved surface. The cleaved surface also was etched by 5% HF solution for one minutes, and it became smoother after HF etching. The main feature in on the surface is the spherical particles with the size of few nanometers, and no aggregated fullerenes appear. The fullerenes are well dispersed in the aerogel matrices.

Lu, W. J .↗
NASA NTRS2000

A Grant from NASA's Office of Space Station Science, Planetary Atmosphere's Program to Boston University

In the past three years of this program we have made contributions to a variety of subjects in research on Jupiter's Atmosphere, the Ultraviolet Spectroscopy of Jupiter, the abundance of CH4 in Pluto's atmosphere, and the emissivity of Pluto's Surface. We also performed work on two projects related to Titan, and an analysis of the visible spectrum of a brown dwarf. The highpoints are briefly summarized and a list of papers supported partly or wholly by this program is also provided.

Yelle, Roger V.↗
NASA NTRS2001

Tethered Formation Configurations: Meeting the Scientific Objectives of Large Aperture and Interferometric Science

With the success of the Hubble Space Telescope, it has become apparent that new frontiers of science and discovery are made every time an improvement in imaging resolution is made. For the HST working primarily in the visible and near-visible spectrum, this meant designing, building, and launching a primary mirror approximately three meters in diameter. Conventional thinking tells us that accomplishing a comparable improvement in resolution at longer wavelengths for Earth and Space Science applications requires a corresponding increase in the size of the primary mirror. For wavelengths in the sub-millimeter range, a very large telescope with an effective aperture in excess of one kilometer in diameter would be needed to obtain high quality angular resolution. Realistically a single aperture this large is practically impossible. Fortunately such large apertures can be constructed synthetically. Possibly as few as three 34 meter diameter mirrors flying in precision formation could be used to collect light at these longer wavelengths permitting not only very large virtual aperture science to be carried out, but high-resolution interferometry as well. To ensure the longest possible mission duration, a system of tethered spacecraft will be needed to mitigate the need for a great deal of propellant. A spin-stabilized, tethered formation will likely meet these requirements. Several configurations have been proposed which possibly meet the needs of the Space Science community. This paper discusses two of them, weighing the relative pros and cons of each concept. The ultimate goal being to settle on a configuration which combines the best features of structure, tethers, and formation flying to meet the ambitious requirements necessary to make future large synthetic aperture and interferometric science missions successful.

Farley, Rodger E.↗
NASA NTRS2003

Finding the Cold Needle in a Warm Haystack: Infrared Imaging Applied to Locating Cryo-cooled Crystals in Loops

Thermally imaging the cryocooling processes of crystals has been demonstrated showing the progression of a cold wave through a crystal from the face closest to the origin of the coldstream ending at the point furthest away. During these studies large volume crystals were clearly distinguished from the loop holding them. Large volume crystals, used for neutron studies, were chosen deliberately to enhance the imaging. The different infrared transmission and reflectance properties of the crystal in comparison to the cryo-protectant are thought to be the parameter that produces the contrast making the crystal visible. As an application of the technology to locating crystals, more small crystals of lysozyme and a bFGF/dna complex were cryo-protected and imaged in large loops. The crystals were clearly distinguished from the vitrified solution. In the case of the bFGF/dna complex the illumination had to be carefully manipulated to enable the crystal to be seen in the visible spectrum. These preliminary results will be presented along with advantages and disadvantages of the technique and a discussion of how it might be applied.

Snell, Edward↗
NASA NTRS1995

Satellite Snow-Cover Mapping: A Brief Review

Satellite snow mapping has been accomplished since 1966, initially using data from the reflective part of the electromagnetic spectrum, and now also employing data from the microwave part of the spectrum. Visible and near-infrared sensors can provide excellent spatial resolution from space enabling detailed snow mapping. When digital elevation models are also used, snow mapping can provide realistic measurements of snow extent even in mountainous areas. Passive-microwave satellite data permit global snow cover to be mapped on a near-daily basis and estimates of snow depth to be made, but with relatively poor spatial resolution (approximately 25 km). Dense forest cover limits both techniques and optical remote sensing is limited further by cloudcover conditions. Satellite remote sensing of snow cover with imaging radars is still in the early stages of research, but shows promise at least for mapping wet or melting snow using C-band (5.3 GHz) synthetic aperture radar (SAR) data. Observing System (EOS) Moderate Resolution Imaging Spectroradiometer (MODIS) data beginning with the launch of the first EOS platform in 1998. Digital maps will be produced that will provide daily, and maximum weekly global snow, sea ice and lake ice cover at 1-km spatial resolution. Statistics will be generated on the extent and persistence of snow or ice cover in each pixel for each weekly map, cloudcover permitting. It will also be possible to generate snow- and ice-cover maps using MODIS data at 250- and 500-m resolution, and to study and map snow and ice characteristics such as albedo. been under development. Passive-microwave data offer the potential for determining not only snow cover, but snow water equivalent, depth and wetness under all sky conditions. A number of algorithms have been developed to utilize passive-microwave brightness temperatures to provide information on snow cover and water equivalent. The variability of vegetative Algorithms are being developed to map global snow and ice cover using Earth Algorithms to map global snow cover using passive-microwave data have also cover and of snow grain size, globally, limits the utility of a single algorithm to map global snow cover.

Hall, Dorothy K.↗