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NASA NTRS1988

Integrating sphere and hemisphere calibration update

This background information relates to the conclusions reached about the GSFC/Optronic calibrations for the 6-foot sphere. Both the hemispherical and the spherical integrating sources were remeasured in February 1988 by two experimenters and the results show a decrease in the output of the sphere. But the discrepancy between GSFC data and Optronic Data remains. The decrease in the output can be accounted for by a correction in the current value of power supplies Number 2 and Number 3. The supplies were running about 1.75 percent high. Minor differences were noted in the short wavelength end of the hemisphere. Efforts to resolve the discrepancy between GSFC and Optronic Labs as well as improve the ability to make more accurate and precise measurements are underway.

Mclean, J. T.↗

NASA NTRS1988

Electron-ion hybrid mode due to transverse velocity shear

Cases in which the velocity shear scale length is larger than the electron gyroradius but much smaller than the ion gyroradius are considered. In this situation, it is found that a hybrid mode with short wavelength and high frequency can be excited.

Ganguli, G.↗

NASA NTRS1988

The spatial distribution of ultraviolet line and continuum emission in Herbig-Haro objects

Archival IUE data and monochromatic CCD images in the optical range are used to compare the spatial distribution of UV and optical emission in HH 1, HH 2, HH 24, HH 32, HH 43, and HH 47. For all six objects, the observed UV radiation is shown to originate in the objects themselves. The results indicate that the C IV and semiforbidden emission-line regions are small. Although the continuum in the IUE short-wavelength range displays a distribution that is broader than that of any measured line emission in the UV or optical range, the continuum distribution in the IUE long-wavelength range is quite narrow.

Lee, M. G.↗

NASA NTRS1988

Hydromagnetic wave heating of low density interstellar gas

The origin of the observed wave spectrum for hot gas in the ISM is considered theoretically. The governing equations for the generation, propagation, and dissipation of compressive waves are reviewed, and particular attention is given to the heating of warm neutral gas and the implications for radio-wave scattering. It is shown that little power from interactions between SN shocks and hot coronal gas reaches short wavelengths, and that scintillation probably does not originate in a warm weakly ionized gas.

Zweibel, Ellen G.↗

NASA NTRS1988

Comparison of Shuttle Imaging Radar-B ocean wave image spectra with linear model predictions based on aircraft measurements

During October 1984, coincident Shuttle Imaging Radar-B synthetic aperture radar (SAR) imagery and wave measurements from airborne instrumentation were acquired. The two-dimensional wave spectrum was measured by both a radar ocean-wave spectrometer and a surface-contour radar aboard the aircraft. In this paper, two-dimensional SAR image intensity variance spectra are compared with these independent measures of ocean wave spectra to verify previously proposed models of the relationship between such SAR image spectra and ocean wave spectra. The results illustrate both the functional relationship between SAR image spectra and ocean wave spectra and the limitations imposed on the imaging of short-wavelength, azimuth-traveling waves.

Monaldo, Frank M.↗

NASA NTRS1989

Observations of aerosol optical depth during the First ISLSCP Field Experiment (FIFE)

Solar radiation measurements were made with a multiwavelength airborne tracking sunphotometer during the First International Satellite Land Surface Climatology Project Field Experiment (FIFE). Data from June 6, and October 11, 1987 are analyzed. Atmospheric optical properties were derived from the data, including total optical depth, aerosol optical depth, aerosol size distribution, aerosol phase function, and aerosol single scattering albedo. The aerosol optical depths for June 6 exhibited a spectral dependence that peaked at short wavelengths, whereas those for October 11 decreased monotonically with wavelength and closely followed an Angstrom wavelength dependence. Also, a unimodal aerosol size distribution was found for the June 6 data, while the October 11 data exhibited a power law size distribution. It is suggested that these differences indicate the need for simultaneous sunphotometer measurements and remotely sensed data.

Spanner, Michael A.↗

NASA NTRS1988

Airborne sensor systems under development at the NASA/NSTL/Earth Resources Laboratory

The operational characteristics of the Airborne Bathymetric System (ABS) MSS and the Airborne Multispectral Pushbroom Scanner (AMPS), which are currently being developed at NASA's Earth Resources Laboratory (ERL), are described. The ABS MSS system scans through a swath width of + or - 40 deg from nadir and the sensor incorporates onboard calibration references for the visible and short-wavelength IR channels. The AMPS uses five separate f/1.8 refractive telecentric lens systems, each incorporating nine optical elements, and a replaceable fixed bandwidth filter.

Anderson, James E.↗

NASA NTRS1988

Ultraviolet observations of SN 1987A - Clues to mass loss

Evidence for a circumstellar shell surrounding SN 1987A is presented, based on UV observations. In May 1987, narrow (less than 1500 km/s) emission lines began to appear in the short wavelength IUE spectra (Wamsteker et al., 1987 and Kirshner et al., 1987) It is suggested that the narrow UV emission lines are due to photoionization of the circumstellar shell by the UV emission expected when the shock hits the surface of the star SK -69 deg 202. Because the gas is N-rich, has a low velocity, and may be located a light-year from the supernova, it is suggested that it was ejected from the progenitor during a red supergiant phase. Also, it is found that the hydrogen mass above a velocity of 6,000 km/s for SN 1987A is between 1 and 6 solar masses.

Kirshner, Robert P.↗

NASA NTRS1988

Mapping in the Oman ophiolite using enhanced Landsat Thematic Mapper images

The level of apparent lithological discrimination possible with Landsat TM images in the Oman are discussed. It is found that by using parts of the short-wavelength IR spectrum, the discrimination revealed by the TM data is sufficiently uniform throughout the Oman ophiolite to produce lithological maps at 1:100,000 scale. Decorrelation stretching of the data produces images in which allows for the recognition of variations in gabbro composition, the identification of small acidic, gabbroic, and ultramafic intrusions, the discrimation of the uppermost mantle from the deeper mantle, the precise location of the Moho, and the delineation of gossans and areas subject to choritic-epidotic alteration.

Abrams, M. J.↗

NASA NTRS1989

An astronomy camera for low background applications in the 1.0 to 2.5 micron spectral region

A description is given of a low-background astronomy camera system based on a short wavelength (1.0-2.5 micron) 128 x 128 focal plane array. The camera is designed to accept either a HgCdTe array for the 1-2.5 micron spectral region or an InSb array for the 3-5 micron spectral region. A cryogenic folded optical system is utilized to control excess stray light along with a cold eight-position filter wheel for spectral filtering. The camera head and electronics will also accept a 256 x 256 focal plane. Engineering evaluation of the system and two engineering runs at the JPL Table Mountain Observatory have been completed. System design, engineering performance, and sample imagery are presented.

Kaki, Said A.↗

NASA NTRS1988

Thematic Conference on Remote Sensing for Exploration Geology, 6th, Houston, TX, May 16-19, 1988, Proceedings. Volumes 1 & 2

Papers concerning remote sensing applications for exploration geology are presented, covering topics such as remote sensing technology, data availability, frontier exploration, and exploration in mature basins. Other topics include offshore applications, geobotany, mineral exploration, engineering and environmental applications, image processing, and prospects for future developments in remote sensing for exploration geology. Consideration is given to the use of data from Landsat, MSS, TM, SAR, short wavelength IR, the Geophysical Environmental Research Airborne Scanner, gas chromatography, sonar imaging, the Airborne Visible-IR Imaging Spectrometer, field spectrometry, airborne thermal IR scanners, SPOT, AVHRR, SIR, the Large Format camera, and multitimephase satellite photographs.

Source record↗

NASA NTRS1989

An analysis of shear failure mechanisms for compression-loaded (+/-theta)s laminates

An analysis of interlaminar and in-plane shear failures for (+/-theta)s composite laminates loaded in uniaxial compression is described. A laminate model is presented that idealizes each ply as a plate supported by an elastic foundation. A nonlinear analysis for plies with short-wavelength initial imperfections is used to determine laminate stresses and interlaminar strains. A failure criterion that uses the results of the nonlinear analysis is introduced.

Shuart, Mark J.↗

NASA NTRS1989

Ultraviolet extinction differences within NGC 6530

Ultraviolet extinction curves are presented for 14 stars in the very young cluster NGC 6530. The variation of the short-wavelength extinction is consistent with that expected based on random errors alone, although the weakest extinction is found only toward the cluster center. Variations significantly larger than the measurement uncertainty are found in the area, width, and central peak position of the 2200 A extinction bump. These parameters are largest in the cluster center and decrease systematically outwards. Physical processes capable of modifying the grains in the H II region containing the cluster are discussed.

Boggs, Don↗

NASA NTRS1989

The relative line strength and intensity of the N II 2143 doublet

The doublet emission from N II at 2139.7 A and 2143.6 A was observed by a 1.4-m scanning spectrometer with 3.1 A resolution in the daytime, high-altitude thermosphere during moderate levels of solar activity. The spectrometer viewed the earth's limb 5 deg below the local horizontal to give a nominal tangent height of 152 km. Both sub band heads of the nitric oxide gamma band system were resolved in the data at the resolution used. The emission features from N II are clearly evident on the short wavelength shoulder of the (1, 0) band. Synthetic profiles of the (1, 0) gamma band and the (0, 3) delta band of nitric oxide were fitted to the data using a chi-square analysis. These contributions were removed from the data leaving a residual emission, considered to be the N II doublet. A chi-square minimization of the data relative to a synthetic intensity profile was done. The minimum was for a line strength ratio between the 2139 A and 2143 A lines of 0.58 + or - 0.08. The mean solar EUV flux deduced from the intensity of the N II emission in this experiment is lower than other reported observations, consistent with a lower solar activity level.

Bucsela, Eric J.↗

NASA NTRS1989

Laser thruster

Laser propulsion can reduce fuel by 57 t to 105 t over chemical propulsion for a 144 t Lunar base, with no significant increase in trip time. Laser propulsion reduces trip time by a factor of 40 to 120 over nuclear electric propulsion and time in radiation belts by a factor of 100 to 1700. Either solar or nuclear driven laser diode arrays could produce multimegawatt beams, typically 3,700 t for a 235 MW laser system. Laser diode arrays have high payoff due to short wavelength (850 nm) and high diode efficiency (70 percent). A dry laser OTV of 8790 kg and 60 percent efficiency can transport a 144 t lunar base. Laser propulsion could carry both personnel and cargo safely to the lunar base.

Jalufka, N. W.↗

NASA NTRS1989

Fourier transform methods in local gravity modeling

New algorithms were derived for computing terrain corrections, all components of the attraction of the topography at the topographic surface and the gradients of these attractions. These algoriithms utilize fast Fourier transforms, but, in contrast to methods currently in use, all divergences of the integrals are removed during the analysis. Sequential methods employing a smooth intermediate reference surface were developed to avoid the very large transforms necessary when making computations at high resolution over a wide area. A new method for the numerical solution of Molodensky's problem was developed to mitigate the convergence difficulties that occur at short wavelengths with methods based on a Taylor series expansion. A trial field on a level surface is continued analytically to the topographic surface, and compared with that predicted from gravity observations. The difference is used to compute a correction to the trial field and the process iterated. Special techniques are employed to speed convergence and prevent oscillations. Three different spectral methods for fitting a point-mass set to a gravity field given on a regular grid at constant elevation are described. Two of the methods differ in the way that the spectrum of the point-mass set, which extends to infinite wave number, is matched to that of the gravity field which is band-limited. The third method is essentially a space-domain technique in which Fourier methods are used to solve a set of simultaneous equations.

Harrison, J. C.↗

NASA NTRS1989

The GRADIO spaceborne gravity gradiometer: Development and accommodation

The European ARISTOTELES mission aims at the determination of the Earth's gravity field at short wavelength with a global coverage. Gravity gradient measurements will be achieved during six months by the GRADIO instrument onboard a dedicated satellite in a near dawn-dusk sun-synchronous orbit at an altitude of 200 km. The objective is an accuracy of better than 5 mgals for gravity anomalies, at ground level for blocks of 1 x 1 deg. According to present knowledge of the potential, the recovery of higher spherical harmonics (degree and order greater than 30) is of main importance. This leads to focus on the variations of the measured components T(sub ij) of the gravity gradient tensor, at frequencies greater than 5 x 10(exp -3) Hz. The resolution, required for the gradiometer is 10(exp -2) Eotvos (i.e., 10(exp -11)/s squared) with an averaging time of 4 s.

Bernard, A.↗

NASA NTRS1989

Improved Si:As BIBIB (Back-Illuminated Blocked-Impurity-Band) hybrid arrays

Results of a program to increase the short wavelength (less than 10 microns) detective quantum efficiency, eta/beta, of Si:As Impurity Band Conduction arrays are presented. The arrays are epitaxially grown Back-Illuminated Blocked (BIB) Impurity-Band (BIBIB) 10x50 detectors bonded to switched-FET multiplexers. It is shown that the 4.7 microns detective quantum efficiency increases proportionately with the thickness of the infrared active layer. A BIB array with a thick active layer, designed for low dark current, exhibits eta/beta = 7 to 9 percent at 4.7 microns for applied bias voltages between 3 and 5 V. The product of quantum efficiency and photoelectric gain, etaG, increases from 0.3 to 2.5 as the voltage increases from 3 to 5 V. Over this voltage range, the dark current increases from 8 to 120 e(-)s(-1) at a device temperature of 4.2 K and is under 70 e(-)s(-1) for all voltages at 2 K. Because of device gain, the effective dark current (equivalent photon rate) is less than 3 e(-)s(-1) under all operating conditions. The effective read noise (equivalent photon noise) is found to be less than 12 electrons under all operating conditions and for integration times between 0.05 and 100 seconds.

Herter, T.↗