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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Skylab radar altimeter - Short-wavelength perturbations detected in ocean surface profiles

Short-wavelength anomalies in sea surface topography, caused by the gravitational effects of major ocean bottom topographic features, have been detected by the radar altimeter aboard Skylab. Some features, such as deep ocean trenches, seamounts, and escarpments, displace the ocean surface by as much as 15 meters over 100-kilometer wavelengths. This experiment demonstrates the potential of satellite altimetry for determining the ocean geoid and for mapping major features of the ocean bottom.

Leitao, C. D.↗
NASA NTRS1975

Callisto - Disk temperature at 3.71-centimeter wavelength

We observed the radio emission of Callisto with a three-element interferometer at the time of the 1973 opposition of Jupiter. Special care was taken to remove the residual, unresolved contribution from Jupiter itself in the antenna side lobes. The resulting disk temperature at a wavelength of 3.71 centimeters, assuming a radius of 2500 + or - 75 kilometers for Callisto, was 101 + or - 25 K. This temperature is much more consistent with emission from a simple dielectric sphere than the considerably higher temperatures that have been reported for wavelengths of 3.5 and 8.2 millimeters.

Berge, G. L.↗
NASA NTRS1975

Mass absorption coefficients of Parylene N at soft X-ray and vacuum-ultraviolet wavelengths

Parylene N was selected as a bandpass filter for the extreme-ultraviolet telescope, flown on the Apollo-Soyuz Test Project in July 1975. The telescope measures stellar and diffuse cosmic radiation in the wavelength region from 45 to 170 A. In connection with this application, a systematic study was conducted of the mass absorption coefficient of the Parylene N. The results of the study for the wavelength region from 44 to 2536 A are reported.

Stern, R.↗
NASA NTRS1975

Comments on the quiet sun brightness distribution at 1.2 mm wavelength

Data on the center-to-limb brightness distribution of the quiet sun at 1.2-mm wavelength are reanalyzed. The observed brightness distribution at this wavelength is plotted along the equatorial direction and analyzed to determine whether it is uniform, limb-brightened, or limb-darkened. It is concluded that at the present time, there is no evidence for a uniform or limb-brightened distribution at 1.2 mm from either an observational or theoretical point of view.

Kundu, M. R.↗
NASA NTRS1976

Solar limb brightening in submillimeter wavelengths

Differential two-beam scans of the sun in submillimeter wavelengths (350 microns to 1 millimeter) indicate limb brightening approaching 1 percent when the cosine of the angle from the normal equals 0.60. The observations also show considerable chromospheric structure, both in active and quiet regions, but with less relative amplitude than at millimeter and centimeter wavelengths. The limited angular resolution of the observing system, together with photometric errors due to fluctuating atmospheric transparency, make the brightness profile of the extreme limb uncertain. The observed degree of limb brightening is considerably less than that consistent with spherically symmetric model atmospheres based on continuum brightness-temperature measurements. The suppression of limb brightening suggests the existence of irregular granular structure with both horizontal and vertical characteristic sizes of the order of 1500 km. High-resolution images in the wings of the K-line show granular structure of about this horizontal scale.

Lindsey, C.↗
NASA NTRS1976

Selection of remote sensing techniques - Surface roughness information from 3 cm wavelength SLAR images

The value of SLAR (Side-Looking Airborne Radar) image data for detecting and measuring small-scale surface roughness is examined, using as an example the Cottonball Basin in Death Valley National Monument, California. The SLAR image was obtained by an X-band (3 cm wavelength) synthetic aperture radar system operated at an altitude of 10,732 m above sea level. The polarization of the transmitted and received signals was horizontal. Film density values were used to produce color hypsometric maps of small-scale surface irregularities. It is shown that semi-quantitative surface roughness information, from uniquely flat surfaces such as the Cottonball Basin, can be obtained by analysis of 3 cm wavelength SLAR images calibrated by limited field measurements. Quantitative roughness data could be obtained with proper consideration of modifying surface and radar system parameters.

Schaber, G. G.↗
NASA NTRS1977

Complex refractive index of Martian dust - Wavelength dependence and composition

The size distribution and complex refractive index of Martian dust-cloud particles observed in 1971 with the Mariner 9 UV spectrometer are determined by matching the observed single-scattering albedo and phase function with Mie-scattering calculations for size distributions of spheres. Values of phase function times single-scattering albedo are presented for 12 wavelength intervals in the range from 190 to 350 nm, and best-fit values are obtained for the absorption index. It is found that the absorption index of the dust particles increases with decreasing wavelength from 350 to about 210 nm and then drops off shortward of 210 nm, with a structural shoulder occurring in the absorption spectrum between 240 and 250 nm. A search for a candidate material that can explain the strong UV absorption yields TiO2, whose anatase polymorph has an absorption spectrum matching that of the Martian dust. The TiO2 content of the dust particles is estimated to be a few percent or less.

Pang, K.↗
NASA NTRS1977

Measurement of wavelength-dependent extinction to distinguish between absorbing and nonabsorbing aerosol particulates

Measurements of spectral transmission factors in smoky optical transmission paths reveal a difference between wavelength exponents of the extinction cross section of high absorption capacity and those of low absorption capacity. A theoretical explanation of this behavior is presented. In certain cases, it is possible to obtain data on the absorption index of aerosol particles in the optical path by measuring the spectral decadic extinction coefficient at, at least, two wavelengths. In this manner it is possible, for instance, to distinguish smoke containing soot from water vapor.

Portscht, R.↗
NASA NTRS1977

Apparent wavelength dependence of v sin i for Zeta Tauri

It was previously reported that the derived projected rotational velocity (v sin i) of the B shell star, Zeta Tau, appeared to depend on the wavelength of the line used in the analysis. This letter documents the apparent wavelength dependence of v sin i for Zeta Tau in order to provide an observational basis against which quantitative explanations can be tested. A value of 300 km/s is adopted for v sin i on the basis of an examination of the visual line spectrum, particularly the lines of He I at 4026 and 4471 A and Mg II at 4481 A. Analysis of the far-UV resonance lines of Si III at 1206 A and Si IV at 1393 and 1463 A in Copernicus spectrograms of Zeta Tau yields a representative value of no more than 150 km/s for v sin i. Gravity darkening of the star's atmosphere and distention of the atmosphere by rapid differential rotation are considered as possible explanations for the discrepancy between the v sin i values determined from the UV and visual lines.

Heap, S. R.↗
NASA NTRS1978

Significance of dual polarized long wavelength radar for terrain analysis

Long wavelength systems with improved penetration capability have been considered to have the potential for minimizing the vegetation contribution and enhancing the surface return variations. L-band imagery of the Arkansas geologic test site provides confirmatory evidence of this effect. However, the increased wavelength increases the sensitivity to larger scale structure at relatively small incidence angles. The regularity of agricultural and urban scenes provides large components in the low frequency-large scale portion of the roughness spectrum that are highly sensitive to orientation. The addition of a cross polarized channel is shown to enable the interpreter to distinguish vegetation and orientational perturbations in the surface return.

Macdonald, H. C.↗
NASA NTRS1978

Multiple wavelength geodesy

An apparatus is being constructed which should be able to measure baselines up to 50 km long with a fractional uncertainty of about 5 x 10 to the -8 power. The instrument will measure both the optical length and the required correction due to the refractivity of the atmosphere, using three wavelengths transmitted in one direction over the path to an active receiver. The three wavelengths are 632.8 nm, 441.6 nm and 3.7 cm. The two endpoint instruments are synchronized using subsidiary return transmissions at 632.8 nm and another telemetry signal. The one-way nature of the system allows an increase in range over existing round-trip systems.

Levine, J.↗
NASA NTRS1979

Airborne infrared and submillimeter astronomical polarization measurements at different wavelengths

Because observations of the Kleinmann-Low region of the Orion Nebula reveal significant polarization in the wavelength range from 1 to 13 micron m, polarization at wavelengths greater than 15 micron were investigated. Far infrared polarization measurements were made of a number of sources using an instrument mounted at the bent cassegrain focus of the Kuiper Airborne Observatory's 90 cm telescope. About two hours of data were obtained on the Orion Nebula on each of two flights, and more careful calibration on Jupiter (assumed to be unpolarized) were obtained on both nights. The data on Orion and Jupiter for three filters are presented. Possible explanations are suggested for reconciling the high polarization observed by others in 1974 with the lower values obtained in this study.

Harwit, M.↗
NASA NTRS1978

Millimeter wavelength spectroscopy of trace atmospheric constituents from the Five College Radio Astronomy Observatory

The Five College Radio Astronomy Observatory system, located in western Massachusetts, is described. It is suggested that high sensitivity in the three-millimeter wavelength band facilitates detection and monitoring of a number of trace molecules in the earth's atmosphere as well as astonomical observation at radio wavelengths. Line formation and radiative transfer in the earth's atmosphere are discussed, and the receiver sensitivity is considered.

Huguenin, G. R.↗
NASA NTRS1979

Interferometric observations of the quiet sun at 8 millimeter wavelength

Results are reported for observations of a quiet region at the center of the sun with an interferometer operating at a wavelength of 8.33 mm and with an east-west baseline giving a maximum angular resolution of 28 arcsec. It is found that strong fluctuations occur over time scales of approximately 10 to 30 min and dominate the data at large hour angles, that smaller and more rapid fluctuations in both amplitude and phase are detected at all hour angles, and that the strong fluctuations are consistent with those that may be produced by the natural time variation of the fringe pattern during observation of a fixed source distribution. The weaker and more rapid fluctuations are tentatively attributed to antenna-tracking variations and the observation of features in a greatly extended source. The results are compared directly with those of two other interferometric studies of the quiet sun at millimeter wavelengths.

Janssen, M. A.↗
NASA NTRS1979

Wide-field electrographic cameras for imagery and spectrography at visual and middle-UV wavelengths

The use of a Kron electrographic detector for wide-field, narrow-band imagery of faint emission nebulosity in the near-UV and visual (3100-6000 A) wavelength interval is described. As an example of the photometric quality of the imagery and of the sensitivity of the instrumentation to diffuse, low-contrast objects, imagery of the Cygnus Loop supernova remnant in the high excitation forbidden line of Ne V 3426 A is presented. In addition, a program to develop electrographic detectors which use cesium telluride photocathodes for broad-band imagery and spectrography in the middle-UV (1650-3100 A) wavelength range is described.

Heckathorn, H. M.↗
NASA NTRS1980

Extending the operating temperature, wavelength and frequency response of HgCdTe heterodyne detectors

Near ideal optical heterodyne performance was obtained at GHz IF frequencies in the 10 micrometer wavelength region with liquid nitrogen cooled HgCdTe photodiodes. Heterodyne NEP's as low as 2.7 x 10 to the minus 20th power W/Hz at 100MHz, 5.4 x 10 to the minus 20th power W/Hz at 1.5 GHz, and 9.4 x 19 to the minus 20th power W/Hz at 3 GHz were achieved. Various physical phenomena which occur within a photodiode and affect heterodyne operation were examined in order to assess the feasibility of extending the operating temperature, wavelength, and frequency response of these HgCdTe photomixers.

Spears, D. L.↗