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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Extreme limb profiles of the sun at far-infrared and submillimeter wavelengths

Thirty, 50, 100, and 200 microns solar limb intensity profiles determined with arcsecond resolution from airborne observations of the occultation of the solar limb during the total eclipse of 1981 July 31 are presented. Two points of particular importance emerge: (1) the longer-wavelength (100 and 200 micron) limbs are significantly brighter than disk center. At 200 microns the extreme limb is about 1.22 times the brightness of disk center. This is consistent with the 6000 K temperature-plateau structure of the model chromospheres of Vernazza, Avrett, and Loeser (1973, Ap. J., 184, 605; 1981; Ap. J. Suppl., 45, 635;) and (2) the longer wavelength limbs are extended significantly further above the visible limb than Vernazza, Avrett, and Loeser predict. These results provide a strong basis for modeling of the solar chromosphere free from the assumption of gravitational-hydrostatic equilibrium.

Lindsey, C.↗
NASA NTRS1984

Results of testing short wavelength HgCdTe hybrid focal plane arrays for earth remote sensing applications

The NASA Imaging Spectrometer program has the objective to develop the next generation of earth remote sensing systems. One part of the program is concerned with the production of advanced short-wavelength mercury cadmium telluride (HgCdTe) hybrid focal plane arrays (FPAs). These arrays are needed for several instruments, including the Shuttle Imaging Spectrometer (SIS), which requires a mosaic of six 64 x 64-element arrays with a cutoff wavelength of 2.5 microns. A device description is provided and the test results are considered. The Airborne Imaging Spectrometer (AIS) is discussed, taking into account an instrument description, focal plane requirements, and AIS results.

Blessinger, M. A.↗
NASA NTRS1986

Measured wavelengths for n = 4 to 2 transitions in Fe XXIV and Fe XXIII

Accurate wavelength measurements for Fe XXIV and Fe XXIII transitions near 8 A and of the type N = 4 to 2 from solar spectra are presented. The resonance transition in the hydrogenlike ion Mg XII is used as a reference. The measured wavelengths are compared with previous ones and with ab initio and semiempirical calculations that include screening parameters in the nonrelativistic, relativistic, and radiative terms.

Seely, J. F.↗
NASA NTRS1985

Simultaneous dual-wavelength VLBI observations of the compact radio source near the Galactic center

Preliminary results from simultaneous VLBI observations at 3.6 and 13 cm confirm that, in this wavelength range, the size of the compact radio source near the Galactic center varies as lambda-squared, where lambda is the wavelength of observation. These results also establish a flux density upper limit at 3.6 cm of 5 mJy for any source in Sgr A West smaller than 8 mas (80 AU).

Marcaide, J. M.↗
NASA NTRS1986

Inversion of 2 wavelength Lidar data for cloud properties

The inversion of the lidar equation to derive quantitative properties of the atmosphere has continued to present considerable difficulty. The results of a study in which Klett's procedure was utilized for the analysis of cloud backscatter measurements made simulataneously at two ruby lidar wavelengths (694nm,347nmm) are presented. With one lidar system a cloud is probed at the two wavelength and the backscatter measured simulataneously by separate receivers. As a result two sigma profiles which should differ only because the wavlength dependence of the scattering. Experimental data presented to demonstrate the effects and the implications of the applications of the inversion method will be discussed.

Pal, S. R.↗
NASA NTRS1986

An intensity-modulated dual-wavelength He-Ne laser for remote sensing of methane

A new type of dual wavelength He-Ne laser is described in which the output power at each of the two wavelengths is modulated with equal amplitude and opposite phase to each other. This laser source can greatly simplify the setup and improve the sensitivity of the differential absorption measurements for the methane detection, as verified by a preliminary experiment. A simple scheme to measure the concentration of methane is also proposed.

Uehara, K.↗
NASA NTRS1986

Backscatter and extinction measurements in cloud and drizzle at CO2 laser wavelengths

The backscatter and extinction of laboratory generated cloud and drizzle sized water drops were measured at carbon dioxide laser wavelengths (predominately at lambda = 10.591 micrometers). Two distinctly different drop size regimes were studied: one which covers the range normally encompassed by natural cloud droplets and the other representative of mist or drizzle sized drops. The derivation and verification of the relation between extinction and backscatter at carbon dioxide laser wavelengths should allow the determination of large cloud drop and drizzle extinction coefficient solely from a lidar return signal without requiring knowledge of the drop size distribution. This result will also apply to precipitation sized drops so long as they are spherical.

Jennings, S. G.↗
NASA NTRS1986

Simultaneous observations of changes in coronal bright point emission at the 20 cm radio and He Lambda 10830 wavelengths

Preliminary results of observations of solar coronal bright points acquired simultaneously from ground based observatories at the radio wavelength of 20 cm and in the He I wavelength 10830 line on September 8, 1985, are reported. The impetus for obtaining simultaneous radio and optical data is to identify correlations, if any, in changes of the low transition-coronal signatures of bright points with the evolution of the magnetic field, and to distinguish between intermittent heating and changes in the magnetic field topology. Although simultaneous observations of H alpha emission and the photospheric magnetic field at Big Bear were also made, as well as radio observations from Owen Valley Radio Interferometer and Solar Maximum Mission (SSM) (O VIII line), only the comparison between He 10830 and the Very Large Array (VLA) radio data are presented.

Habbal, Shadia R.↗
NASA NTRS1986

Rapid spectral and flux time variations in a solar burst observed at various dm-mm wavelengths and at hard X-rays

A solar burst was observed with high sensitivity and time resolution at cm-mm wavelengths by two different radio observatories (Itapetinga and Algonquin), with high spectral time resolution at dm-mm wavelengths by patrol instruments (Sagamore Hill), and at hard X-rays (HXM Hinotori). At the onset of the major burst time structure there was a rapid rise in the spectral turnover frequency (from 5 to 15 GHz), in about 10s, coincident to a reduction of the spectral index in the optically thin part of the spectrum. The burst maxima were not time coincident at the optically thin radio frequencies and at the different hard X-ray energy ranges. The profiles at higher radio frequencies exhibited better time coincidence to the high energy X-rays. The hardest X-ray spectrum (-3) coincided with peak radio emission at the higher frequency (44 GHz). The event appeared to be built up by a first major injection of softer particles followed by other injections of harder particles. Ultrafast time structures were identified as superimposed on the burst emission at the cm-mm high sensitivity data at X-rays, with predominant repetition rates ranging from 2.0 to 3.5 Hz.

Zodivaz, A. M.↗
NASA NTRS1987

Surface bidirectional reflectance properties of two southwestern Arizona deserts for wavelengths between 0.4 and 2.2 micrometers

Surface bidirectional reflectance characteristics are presented for the Sonora Desert and the Mohawk Valley at solar zenith angles of 13, 31, and 57 degs at wavelengths between 0.4 and 1.6 microns. Nadir reflectance values are presented for wavelengths between 0.4 and 2.2 microns for solar zenith angles of 13, 17.5, 27, 31, 45, 57, and 62 degs. Data were taken from a helicopter during May l985 in support of an Earth Radiation Budget Experiment (ERBE), a Stratospheric Aerosol Gas Experiment (SAGE II), and an Advanced Very High Resolution Radiometer (AVHRR) satellite validation experiment.

Whitlock, Charles H.↗
NASA NTRS1986

High-speed dual-wavelength demultiplexing and detection in a monolithic superlattice p-i-n waveguide detector array

High-speed (1 Gbit/x) dual-wavelength demultiplexing and detection in a monolithic linear array of superlattice p-i-n photodetectors in a waveguide configuration is demonstrated. A crosstalk attenuation of 28 dB was achieved between two digital transmission channels with an interchannel wavelength spacing of 30 nm. The device performance is a result of an enhanced electroabsorption due to the quantum-confined Stark effect in the superlattice p-i-n diodes.

Larsson, A.↗
NASA NTRS1986

Wavelength dependence of position angle in polarization standards

Eleven of the 15 stars on Serkowski's (1974) list of 'Standard Stars with Large Interstellar Polarization' were investigated to determine whether the orientation of the plane of their linear polarization showed any dependence on wavelength. Nine of the eleven stars exhibited a statistically significant wavelength dependence of position angle when measured with an accuracy of about 0.1 deg standard deviation. For the majority of these stars, the effect is caused primarily by intrinsic polarization. The calibration of polarimeter position angles in a celestial coordinate frame must evidently be done at the 0.1 deg level of accuracy by using only carefully selected standard stars or by using other astronomical or laboratory methods.

Dolan, J. F.↗
NASA NTRS1986

Extreme limb profiles of the sun at far-infrared and submillimeter wavelengths

Thirty, 50, 100, and 200 microns solar limb intensity profiles determined with arcsecond resolution from airborne observations of the occultation of the solar limb during the total eclipse of July 31, 1981, are presented. Two points of particular importance emerge: (1) the longer-wavelength (100 and 200 micron) limbs are significantly brighter than disk center. At 200 microns the extreme limb is about 1.22 times the brightness of disk center. This is consistent with the 6000 K temperature-plateau structure of the model chromospheres of Vernazza, Avrett, and Loeser (1973, Ap. J., 184, 605; 1981; Ap. J. Suppl., 45, 635); and (2) the longer wavelength limbs are extended significantly further above the visible limb than Vernazza, Avrett, and Loeser predict. These results provide a strong basis for modeling of the solar chromosphere free from the assumption of gravitational-hydrostatic equilibrium.

Lindsey, C.↗
NASA NTRS1986

Microchannel plates and image detection at soft X-ray wavelengths

Detector systems based on the high-gain microchannel plate (MCP) electron multiplier have been used extensively for imaging at soft X-ray wavelengths both on the ground and in space. The latest pulse-counting electronic readout systems provide zero readout-noise, spatial resolutions (FWM) of 25 microns or better and can determine the arrival times of detected photons to an accuracy of the order of 100 ns. These systems can br developed to produce detectors with active areas of 100 mm in diameter or greater. The use of CsI photocathodes produces very high detective quantum efficiencies to wavelengths between about 100 and 1A (0.1 to 10 keV) with moderate energy resolution. The operating characteristics of the different types of soft X-ray MCP detector systems are described, and the prospects for future developments are discussed.

Timothy, J. G.↗
NASA NTRS1986

Evaluation of the microwave spectrum of Venus in the 1.2-22 centimeter wavelength range based on laboratory measurements of constituent gas opacities

Laboratory measurements of the microwave (1.2-22.3 cm) spectrum properties of Venus' gaseous atmospheric constituents were performed using an apparatus for simulating conditions of the middle atmosphere of Venus (gaseous H2SO4 + CO2 at 1 to 6 atm). The results have shown that at wavelengths longer than 1.8 cm, gaseous H2SO4 and CO2 are the predominant microwave absorbers, while at wavelengths from 1.2 to 1.8 cm, SO2 and CO2 are the predominant absorbers. These results were used to develop a model for the microwave emission spectrum of Venus, which correlated well with microwave observations of this planet.

Steffes, Paul G.↗
NASA NTRS1986

A global-scale model of aerosol backscatter at CO2 wavelengths for satellite-based lidar sensors

The status of a global-scale model of background aerosol backscatter cross-sections at CO2 wavelengths is described. The model needs, strategy, concept, parameters, and capabilities are addressed, and the data base is discussed, concluding data selection, CO2 backscatter measurements, aerosol optical measurements, aerosol microphysical measurements, water vapor measurements, and data analysis. Strong evidence is reported for a 'universal' background tropospheric aerosol population. Typical background backscatter values at CO2 wavelengths appear to be about 3 x 10 to the -11th to 8 x 10 to the -11th/m/sr. Background signatures are evident in most aerosol data sets which have global-scale coverage in space or time.

Bowdle, David A.↗
NASA NTRS1986

Absolute absorption cross sections of ozone in the 185- to 350-nm wavelength range

The absorption cross sections of ozone have been measured in the wavelength range 185-350 nm and in the temperature range 225-298 K. The absolute ozone concentrations were established by measuring the pressure of pure gaseous samples in the 0.08to 300-torr range, and the UV spectra were recorded under conditions where less than 1 percent of the sample decomposed. The temperature dependence is significant for wavelengths longer than about 280 nm. The absorption cross-section values around 210 nm were found to be about 10 percent larger than the previously accepted values.

Molina, L. T.↗
NASA NTRS1987

Long-wavelength absorption by fractal dust grains

The far-infrared and submillimeter absorption properties of random aggregates of conducting spheres have been studied as a possible source for the long-wavelength absorption of interstellar dust grains. The complex shapes of random aggregates have various fractal dimensions, depending on the process that forms them. The long wavelength absorption versus frequency is affected more by the shape of a conducting grain than by its composition.

Wright, Edward L.↗