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At least 1,387 records · Page 77
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NASA NTRS1985

A Preliminary Investigation of Systematic Noise in Data Acquired with the Airborne Imaging Spectrometer

Systematic noise is present in Airborne Imaging Spectrometer (AIS) data collected on October 26, 1983 and May 5, 1984 in grating position 0 (1.2 to 1.5 microns). In the October data set the noise occurs as 135 scan lines of low DN's every 270 scan lines. The noise is particularly bad in bands nine through thirty, restricting effective analysis to at best ten of the 32 bands. In the May data the regions of severe noise have been eliminated, but systematic noise is present with three frequencies (3, 106 and 200 scan lines) in all thirty two bands. The periodic nature of the noise in both data sets suggests that it could be removed as part of routine processing. This is necessary before classification routines or statistical analyses are used with these data.

Masuoka, E.↗
NASA NTRS1985

Scattered light in the IUE spectra of Epsilon Aurigae

As a result of this work it was found that light scattered from the longer wavelengths constitutes a small but non-negligible, wavelength and time dependent fraction of the measured flux in the far UV. The reality of the UV excess has not been unambigiously ruled out. However, it is noted that there are still uncertainties in the assumed scattering profile. New measurements of the scattering properties of the cross disperser grating are planned in order to verify the results of Mount and Fastie and extend the wavelength coverage into the far wings of the profile. The results of these measurements will no doubt reduce some of these uncertainties. For the present, it is felt that the BCH approach is a significant improvement over the methods heretofore available for the treatment of scattered light in IUE spectra.

Aitner, B.↗
NASA NTRS1985

Advanced Moisture and Temperature Sounder (AMTS) baseline 5 study report

An Advanced Moisture and Temperature Sounder (AMTS) passive infrared atmospheric sounding system is described. Instrument requirements are developed. Parametric and scaling equations for a grating spectrometer instrument approach are developed which define detector noise limited performance in terms of instrument, orbit, and spatial coverage parameters. Instrument design criteria are developed and a baseline instrument design is presented. Error sources are identified and corresponding system error component values are estimated. Within narrow limits, the highest level of performance achievable with a stand alone infrared sounder using current state of the art technology is established. Additional trade offs necessary to establish a reasonably optimal system design in terms of performance, cost, and risk are identified.

Evans, N. L., Jr.↗
NASA NTRS1985

Interstellar Medium Absorption Profile Spectrograph (IMAPS)

The design and fabrication of an objective-grating echelle spectrograph to fly on sounding rockets and record spectra of stars from approximately 920 to 1120A with a resolving power lambda/delta lambda = 200,000 is discussed. The scientific purpose of the program is to observe, with ten times better velocity resolution than before, the plentiful absorption lines in this spectral region produced by atoms, ions and molecules in the interstellar medium. In addition, an important technical goal is to develop and flight-quality a new ultraviolet, photon-counting image sensor which has a windowless, opaque photocathode and a CCD bombarded directly by the accelerated photoelectrons. Except for some initial difficulties with the performance of CCDs, the development of the payload instrument is relatively straightforward and our overall design goals are satisfied. The first flight occurred in late 1984, but no data were obtained because of an inrush of air degraded the instrument's vacuum and caused the detector's high voltage to arc. A second flight in early 1985 was a complete success and obtained a spectrum of pi Sco. Data from this mission are currently being reduced; quick-look versions of the spectra indicate that excellent results will be obtained. Currently, the payload is being reconfigured to fly on a Spartan mission in 1988.

Jenkins, E. B.↗
NASA NTRS1986

Observations of the J = 10 manifold of the pure rotational band of phosphine on Saturn

Saturn was observed in the vicinity of the J = 10 manifold of the pure rotational band of phosphine on 1984 July 10 and 12 from NASA's Kuiper Airborne Observatory with the facility far-infrared cooled grating spectrometer. On each night observations of the full disk plus rings were made at 4 to 6 discrete wavelengths which selectively sampled the manifold and the adjacent continuum. The previously reported detection of this manifold is confirmed. After subtraction of the flux due to the rings, the data are compared with disk-averaged models of Saturn. It is found that PH3 must be strongly depleted above the thermal inversion (approx. 70 mbar). The best fitting models consistent with other observational constaints indicate that PH3 is significantly depleted at even deeper atmospheric levels ( or = 500 mbar), implying an eddy diffusion coefficient for Saturn of 10 to the 4 cm sq/sec.

Haas, M. R.↗
NASA NTRS1985

The Imaging Spectrometric Observatory

Design and performance features of the Imaging Spectrometric Observatory (ISO) first flown on Spacelab 1 for atmospheric, earth surface and stellar monitoring are outlined. The ISO has five grating spectrometers fitted with CCD arrays for simultaneously gathering spectral and spatial data. The instrument covered the 300-12,700 A range on the Spacelab 1 flight, when it was mounted on a pallet and used for atmospheric scans at high solar zenith angles. A future mission is planned which will include limb-viewing of OH, NO, ClO and NO2 radicals in the middle atmosphere to complement the data collected in the Upper Atmosphere Research Satellite program. Technical details are presented of the instrument components and ground- and balloon-borne test results.

Torr, D. G.↗
NASA NTRS1986

Advanced X-ray Astrophysics Facility (AXAF) instrumentation

The instrumentation planned for the Advanced X-ray Astrophysics Facility (AXAF), a space-based observation platform for the 1990s, is described. The AXAF will feature a grazing incidence telescope at the end of the observatory and four independently selected instruments at the other end, including: a CCD imaging spectrometer; a Bragg crystal spectrometer; and two transmission grating spectrometers located directly behind the telescope to detect first order spectral images. The instruments are currently in the definition phase to be followed by design and development starting in the late 1980s. A detailed schematic diagram of the Bragg crystal imaging spectrometer is provided.

Winkler, C. E.↗
NASA NTRS1985

The application of contraction theory to an iterative formulation of electromagnetic scattering

Contraction theory is applied to an iterative formulation of electromagnetic scattering from periodic structures and a computational method for insuring convergence is developed. A short history of spectral (or k-space) formulation is presented with an emphasis on application to periodic surfaces. To insure a convergent solution of the iterative equation, a process called the contraction corrector method is developed. Convergence properties of previously presented iterative solutions to one-dimensional problems are examined utilizing contraction theory and the general conditions for achieving a convergent solution are explored. The contraction corrector method is then applied to several scattering problems including an infinite grating of thin wires with the solution data compared to previous works.

Brand, J. C.↗
NASA NTRS1986

A faint object spectrometer for the infrared

A cryogenic astronomical spectrometer for the NASA Infrared Telescope Facility is described. This spectrometer will employ an array of at least 20 detectors and provide a resolving power of 100 to 1500 at 1-5 microns. The resolving power will be adjustable by changing gratings.

Tokunaga, A. T.↗
NASA NTRS1985

Observations of the J = 10 manifold of the pure rotational band of phosphine on Saturn

Saturn was observed in the vicinity of the J = 10 manifold of the pure rotational band of phosphine on 1984 July 10 and 12 from NASA's Kuiper Airborne Observatory with the facility far-infrared cooled grating spectrometer. On each night observations of the full disk plus rings were made at 4 to 6 discrete wavelengths which selectively sampled the manifold and the adjacent continuum. The previously reported detection of this manifold is confirmed. After subtraction of the flux due to the rings, the data are compared with disk-averaged models of Saturn. It is found that PH3 must be strongly depleted above the thermal inversion (approx. 70 mbar). The best fitting models consistent with other observational constraints indicate that PH3 is significantly depleted at even deeper atmospheric levels (or = 500 mbar), implying an eddy diffusion coefficient for Saturn of 10 to the 4 cm sq/sec.

Haas, M. R.↗
NASA NTRS1986

Diffraction effects and special advantages in electronic heterodyne moire deflectometry

Effects of diffraction on the performance of electronic heterodyne readout of moire fringes are investigated. The sensitivity, accuracy, and resolution of the system are calculated, and it is shown that these features are significantly improved compared with the conventional intensity moire readout technique. The sensitivity of the system can be tripled without changing the distance between gratings. The system was evaluated experimentally by measuring the refractive-index derivatives of a weak phase object consisting of a large KD(asterisk)P crystal. Effects of nonlinear fringe modulation were studied both theoretically and experimentally. It is shown that in this case the electronic phase is not linearly related to the fringe shift, and calibration of the system is necessary.

Stricker, J.↗
NASA NTRS1985

Advanced X-ray Astrophysics Facility (AXAF) science instrumentation

AXAF is to be equipped with a high performance X-ray telescope for the conduction of detailed astrophysics research. The observatory is to be serviced by the Space Station or the Shuttle, depending on capabilities during the AXAF operational period. The AXAF is to utilize the wavelength band from 1.2 A to 120 A. Attention is given to the AXAF science team, the AXAF observatory characteristics, the AXAF science instrument definition program, the Advanced Charge Coupled Device (CCD) Imaging Spectrometer (ACIS), the High Resolution Camera (HRC), the Bragg Crystal Spectrometer (BCS), the X-ray Spectrometer (XRS), the transmission gratings, and the program schedule.

Dailey, C. C.↗
NASA NTRS1986

Evidence for a low-density component in the broad-line region of Seyfert 1 galaxies

It is found that the forbidden 4959-5007 A broad O III lines, good candidates for the excess shelf emission, are found in the vicinity of H-beta in Seyfert 1 galaxy spectra. The shelf-study method used to remove Fe II assumes that the profiles of the contributors to the shelf are known, and that subtraction of these contributors in the correct amount will result in a fairly smooth H-beta profile. Data were obtained with the Ohio State University Image-Dissector Scanner with a 600 line/mm grating, on a 1.8-m reflector. The estimated cloud electron density of 1 billion/sq cm is at the low end of those used for BLR photoionization models. The presence of a broad residual emission feature in the neighborhood of 5050 A after subtraction of the shelf is thought to be the result of a weak broad emission in this range from yet another species.

Crenshaw, D. M.↗
NASA NTRS1985

Shear strain anomalies in composite beam specimens by moire interferometry

Experimental analyses were performed for determination of in-plane deformations and shear strains in unidirectional and quasi-isotropic graphite-epoxy beams. Forty-eight-ply beams were subjected to five-point and three-point flexure. Whole-field measurements were recorded at load levels from about 20 percent to more than 90 percent of failure loads. Contour maps of U and W displacement fields were obtained by moire interferometry, using reference gratings of 2400 lines/mm. Clearly defined fringes with fringe orders exceeding 1000 were obtained. Whole-field contour maps of shear strains were obtained. Various anomalous effects were detected in the displacement fields. Their analysis indicated excess shear strains in resin-rich zones in regions of shear tractions; free-edge shear strains in quasi-isotropic specimens in regions of normal stresses, and shear stresses associated with cyclic shear compliances of quasi-isotropic laminates in regions of shear tractions. Their contributions could occur independently or in superposition. Qualitative analyses addressed questions of the effect of specimen overhang, nonlinearity, and characteristics of five-point and three-point flexure tests.

Post, D.↗
NASA NTRS1986

Observation of radiative surface plasmons in metal-oxide-metal tunnel junctions

A peak in the UV region of the spectrum of light emitted from metal-oxide-metal (MOM) tunnel junctions has been observed at room temperature. Both the amplitude and wavelength of the peak are sensitive to applied junction bias. The UV peak corresponds to the normal or radiative surface plasmon mode while a visible peak, also present in the present spectra and reported in past MOM literature, is due to the tangential or nonradiative mode. The radiative mode requires no surface roughness or gratings for photon coupling. The results show that it is possible to obtain radiative surface plasmon production followed by a direct decay into photons with MOM tunnel diodes. A MOM diode with a double anode structure is found to emit light associated only with the nonradiative mode. The thickness dependence of the UV peak, along with the experimental results of the double anode MOM diode and the ratio of the UV peak to visible peak, support the contention that the UV light emission is indeed due to the radiative surface plasmon.

Donohue, J. F.↗
NASA NTRS1986

In-flight analysis of IUE cross-disperser scattered light

The scattered light properties of the IUE (International Ultraviolet Explorer) cross-disperser gratings are investigated using in-flight data of the emission spectrum of Comet Bradfield (1979X). The scattering function in the vicinity of H I Lyman alpha at 1216 angstroms is found to be significantly lower than that derived from either the laboratory measurements of Mount and Fastie (1978) or the analysis by Basri et al. (1985) of cool star observations.

Feldman, P. D.↗
NASA NTRS1986

Enhanced acetylene emission near the north pole of Jupiter

The present paper is concerned with observations of acetylene fundamental and hot band vibrational emission lines from the planet Jupiter. It is pointed out that the observation of a polar bright spot in the atmosphere of Jupiter is characterized by an enhancement in the individual lines of C2H2 which can be interpreted as an enhancement in the acetylene abundance. However, a purely thermal effect, or non-LTE phenomena cannot be excluded. The intensity of the observed hot band lines is also consistent with either hypothesis. The reported observations were performed with a cooled Fabry-Perot Grating Spectrometer (FPGS). Observations and instrumentation are considered in detail along with the calculation of synthetic spectra on the basis of a line-by-line computation, and the interpretation of the obtained data.

Drossart, P.↗