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NASA NTRS1982

Airborne multispectral linear array instruments at Goddard Space Flight Center

The fabrication of airborne instruments is contributing to the development of multispectral linear array technology at NASA's Goddard Space Flight Center. The linear array pushbroom radiometer (LAPR-I), was built to demonstrate capabilities for acquiring digital image data using linear arrays. The LAPR-I employed three arrays of 512 silicon photodiodes each to simultaneously acquire three channels of data for spectral bands within the visible and near-infrared portions of the spectrum. A second instrument, LAPR-II, uses four arrays each consisting of 512 silicon detectors. A filter wheel containing six spectral filters is used in conjunction with each array to allow filter changes in flight. This capability will facilitate studies into the utility of various bands within the visible and near infrared portions of the spectrum. The LAPR-II's aircraft mounting will allow off-nadir pointing (plus-or-minus 50 deg fore-and-aft and side-to-side) which will enable investigations of the radiometric and geometric effects of off-nadir viewing. A short wave infrared radiometer is also described.

Irons, J. R.↗

NASA NTRS1982

The optical spectrum of R136a - The central object of the 30 Doradus nebula

R136 (HD 38268) is the brightest member of the compact cluster of stars at the center of the 30 Doradus Nebula, a massive H II region in the Large Magellanic Cloud (LMC). The far-ultraviolet luminosity is equivalent to at least 1000 ordinary O type stars. Optically, R136 is an unresolved patch corresponding to a linear extent of about 0.7 pc. Several components are known to be present, of which R136a is the brightest. A quantitative description of the optical spectrum of R136a has not been available in the literature. The present investigation is concerned with the analysis of spectrograms in the visible region. It is found that the optical spectrum of R136a shows broad but rather weak emission lines of ions which are frequently seen in early WN-type stars. The centroid of H-alpha is displaced by approximately 100 km/s redward of the nebular H-alpha emission. The Balmer series is visible, in absorption, up to H11.

Ebbets, D. C.↗

NASA NTRS2014

On-Orbit Radiometric Characterization of OLI (Landsat 8) for Applications in Aquatic Remote Sensing

Landsat-8 carries two separate sensors, namely the Operational Land Imager (OLI) and the Thermal Infrared Radiometer Suite (TIRS), that image the earth surface throughout the visible and thermal portions of the spectrum. Compared to Landsat heritage sensors, the OLI has enhanced features, which include its 12-bit radiometric resolution and the addition of a band centered at 443 nm. The dramatically improved data quality/quantity expands existing applications of Landsat imagery in aquatic sciences from the retrieval of bio-geochemical properties, such as near-surface concentrations of chlorophyll-a (CHL) and total suspended solids (TSS), to benthic mapping. This study offers analysis of OLI's absolute radiometric performance over bodies ofwater using benchmark observations, namely the top-of-atmosphere (TOA) ocean color observations and marine in situ radiometric measurements. Sensor-to-sensor comparisons are performed to derive gain factors (g1) from near-concurrent observations in TOA radiance and reflectance domains. The gains in the radiance domain were further validated/adjusted by determining a second set of gains (g2) via analysis of OLI-derived water-leaving radiance, i.e., L(sub w) (gamma), against in situ measurements made either at the Ocean Color AErosol RObotic NETwork (AERONETOC) sites or during field campaigns. The analyses yield the OLI calibration uncertainties that need to be accounted forwhen studying aquatic environments. Itwas found that, for the visible and near-infrared channels, the OLI radiometric responses, on average, are well in agreement (b 2 % discrepancies) with the TOA radiances estimated by ocean color satellites or those predicted by models based onmeasurements of aquatic and atmospheric properties. However, the TOA radiance at the new 443-nm band is found to be, on average, 3.4 % larger than the reference observations. The inter-sensor comparisons in the reflectance domain, however, indicated slightly different results with the OLI responses being low in the blue bands. To enhance the retrieval accuracy of aquatic-science products from OLI datasets, sets of temporally averaged gains (radiance and reflectance) are derived and recommended for use prior to the retrieval of in-water products.

Remote Sensing↗

NASA NTRS1973

Red clouds in reducing atmospheres

A dark reddish-brown high-molecular weight polymer is produced by long wavelength ultraviolet irradiation of abundant gases in reducing planetary atmospheres. The polymer is examined by paper chromatography, mass spectrometry, and infrared, visible, and ultraviolet spectroscopy. High carbon-number straight-chain alkanes with NH2 and, probably, OH and C = O groups are identified, along with amino acids. There are chemical similarities between this polymer and organic compounds recovered from carbonaceous chondrites and precambrian sediments. The visible and near-ultraviolet transmission spectrum of the polymer shows its absorption optical depth to be redder than lambda(-2) and perhaps similar in coloration to the clouds of Jupiter, Saturn, and Titan. The nitrile content is small, and the polymer should be semitransparent in the 5 micrometer atmospheric window. Such polymers may be a common constituent of clouds in the outer solar system and on the early earth.

Khare, B. N.↗

NASA NTRS1975

Infrared tunable laser: A concept

Apparatus in which laser wavelengths of two dyes are mixed in intracavity, nonlinear crystal provides intense source of coherent laser radiation which is tunable from visible through infrared wavelengths of electromagnetic spectrum.

Billman, K. W.↗

NASA NTRS1979

Identification of HgO/x/ species by matrix isolation spectroscopy

The condensation of Hg atoms in an ozone-doped argon matrix gas with irradiation from a medium-pressure mercury arc lamp at 10 K resulted in the formation of several trapped HgO(x) species. Tentative identification of HgO has been made from absorption bands appearing in the visible and IR regions of the spectrum based on (O-16)2 and (O-18)2 isotope studies. The following spectroscopic constants were obtained: nu(00) = 14634 cm, nu(1) = 548 cm, and nu(11) = 676 cm. Some qualitative evidence was obtained for the existence of HgO2.

Butler, R.↗

NASA NTRS1980

Titan aerosols - Optical properties and vertical distribution

An analysis of Titan's solar phase variation as a function of wavelength together with the continuum geometric albedo makes it possible to set limits on the real part of the refractive index and on the average particle size of the aerosol component of Titan's atmosphere of between about 1.5 and 2.0 and between 0.20 microns and about 0.35 microns, respectively. If the real part of the refractive index is known the average particle size can be determined to within a few percent, and varies inversely with the real part of the refractive index. Using this information in a two-layer model of a methane-aerosol atmosphere and comparing the result with Titan's visible and near-infrared methane spectrum leads to the conclusion that the top layer of Titan's atmosphere contains 0.01 km atm of methane and 2.5 extinction optical depths of aerosol, while the data are consistent with a bottom layer containing 2.2 km atm of methane and about 7.5 aerosol optical depths for a real part of the refractive index equal to 1.7 and an average particle size of 0.25 microns.

Rages, K.↗

NASA NTRS1980

Ultraviolet spectroscopic observations of VV Cephei

Observations with the International Ultraviolet Explorer satellite (IUE) of the recent egress of the eclipsing binary VV Cep(M2Iabep + B) are presented. Egress in the ultraviolet lagged behind the visible egress by 2 to 3 months, as a result of higher opacity of the M star atmosphere in the ultraviolet. Shortly after visible egress, the low-dispersion spectrum from 1200-1900 wavelengths was dominated by fluorescent emission lines arising in the atmosphere of the M star and excited by the ultraviolet continuum of the hot companion. High-dispersion spectra show a hot continuum blanketed by absorption lines, some of which weaken or disappear as the egress continues. A year after eclipse, the absorption spectrum is still too complex to permit determination of a spectral type for the hot companion. The Mg II h and k lines both exhibit asymmetric double-peaked emission features indicative of an expanding chromosphere in the M supergiant.

Hagan, W.↗

NASA NTRS1982

Portable Radiometer Monitors Plant Growth

Three-band hand-held spectral radiometer measures electromagnetic energy reflected from plant canopies in the visible and infrared portions of the spectrum. It is mobile and easy to use for rapid, repeated measurements. Radiometer probe is held level over plant canopy, readout range switches are set and measurements are recorded. Chlorophyll content, leaf area index and leaf water content can be quickly and easily measured.

Tucker, C. J., III↗

NASA NTRS1980

Ultraviolet albedo of Comet West /1976 VI/

The nature of the dust scattered radiation shown in the ultraviolet spectrum of Comet West is analyzed. The continuum of solar radiation scattered by cometary dust is detected to wavelengths as short as 2100 A and is found to follow closely the solar spectrum. The flux from the entire visible coma is included in the spectrometer slit. A comparison of the ultraviolet with the visible solar flux gives the ratio of the albedo at 2700 A to that of 5500 A as about 0.3. Even with all the uncertainties included (the absolute calibration uncertainty is plus or minus 15%), the evidence for strong reddening between the visible and the ultraviolet is clear. A further decrease in albedo is found near 2200 A. The value of the visible albedo of 0.2 is used to derive a value of 0.6 for the cometary albedo at 2700 A. This value is similar to that found for the moon and lunar dust in this spectral region.

Feldman, P. D.↗

NASA NTRS1983

A stochastic atmospheric model for remote sensing applications

There are many factors which reduce the accuracy of classification of objects in the satellite remote sensing of Earth's surface. One important factor is the variability in the scattering and absorptive properties of the atmospheric components such as particulates and the variable gases. For multispectral remote sensing of the Earth's surface in the visible and infrared parts of the spectrum the atmospheric particulates are a major source of variability in the received signal. It is difficult to design a sensor which will determine the unknown atmospheric components by remote sensing methods, at least to the accuracy needed for multispectral classification. The problem of spatial and temporal variations in the atmospheric quantities which can affect the measured radiances are examined. A method based upon the stochastic nature of the atmospheric components was developed, and, using actual data the statistical parameters needed for inclusion into a radiometric model was generated. Methods are then described for an improved correction of radiances. These algorithms will then result in a more accurate and consistent classification procedure.

Turner, R. E.↗

NASA NTRS1985

Shuttle glow emissions due to radiative relaxation of highly vibrationally excited NO molecules produced by surface reflection

A new mechanism is proposed for the Space Shuttle glow, which is due to the radiative relaxation of ambient nitric-oxide molecules that are excited to very high vibrational levels by collisions with the Shuttle surface. Many of the particles colliding with the Shuttle surface at a very high speed (about 8 km/sec) would bounce off, exciting vibrational and rotational motions of molecules up to the level of vibrational quantum number v not greater than 35. Radiative transfer from these high levels should cause emissions in the spectrum range from infrared (IR) to visible red depending upon the transition paths. A perturbation method is used to calculate the transition probability and the emission intensity for the transitions of Delta-v not greater than 4. The result indicates that the Delta-v not greater than 4 transitions from high vibrational levels dominates the other transitions; the Delta-v = 4 transitions generally occur at the IR range.

Shimazaki, T.↗

NASA NTRS1985

Remote sensing of atmosphere-surface interaction parameters

Examples are given of the accuracy of the results obtained from the HIRS 2/MSU (High Resolution Infrared Sounder and Microwave Sounding Unit) analysis of ocean, atmosphere, and land parameters. Sea surface temperatures are compared with available ship and buoy radiosonde data, and land surface temperatures are compared with shelter temperatures. The seasonal change in land and ocean skin surface temperature is reviewed. The distribution of clouds is examined and their opacities in the visible and infrared parts of the spectrum are compared.

Chahine, M. T.↗

NASA NTRS1986

Detection of a 'rotating' gas cloud 100 kiloparsecs in diameter surrounding 3C 275.1, a quasar at the center of a rich cluster of galaxies

The distorted radio quasar 3C 275.1 (z = 0.55) is the first QSO found to lie at the center of a rich cluster of galaxies. The quasar is surrounded by an extremely large elliptical nebulosity whose major axis exceeds 100 kpc. Spectroscopic observations of this nebulosity were obtained, with the spectrograph slit aligned along the nebulosity's major axis. The spectrum of the nebulosity in the visible is dominated by O II and O III forbidden emission lines, which yield a well-defined 'solid-body rotation curve' extending 40 kpc from the quasar nucleus, a rotation curve very different from those of normal spiral galaxies. The 3C 275.1 nebulosity is both the largest yet discovered around a quasar and the first in which organized large-scale motions (rotation?) have been identified. The nebulosity may be residue from multiple tidal interactions with cluster members, or it may be accumulated material from a 'cooling flow' of the type seen in low-redshift clusters which are X-ray sources.

Hintzen, P.↗

NASA NTRS1989

Measuring and modeling spectral characteristics of a tallgrass prairie

This study was conducted to evaluate the diurnal and seasonal, spectral reflectance characteristics of burned and unburned areas of a tallgrass prairie, based on field measurements and models of radiation transport in plant canopies. Burning of the senescent vegetation, resulting from the previous years' growth, is a common management practice, which results in improved productivity and affects the succession of grass species. The burned and unburned grass canopies showed distinctly different, diurnal and seasonal, spectral reflectance characteristics in the visible and infrared regions of the spectrum. These were attributed to the differences in development of the two plant canopies and the azimuthal differences in sensor-sun-canopy positions during field measurements of spectral reflectance. The radiation transfer model properly simulated the diurnal spectral behavior of the two canopies. The simulated, seasonal, spectral reflectance values for the unburned grass canopy were greater than the measured ones, because of limitations in proper representation of the layer of senescent vegetation in the model.

Asrar, G.↗

NASA NTRS1990

Experimental investigations of low-energy (4 to 40 eV) collisions of O(-)(P2) ions and O(P3) atoms with surfaces

Using a newly-developed, magnetically confined source, low-energy, ground state oxygen negative ions and neutral atoms are generated. The energy range is variable, and atom and neutrals have been generated at energies varying from 2 eV to 40 eV and higher. It was found that the interaction of these low-energy species with a solid magnesium fluoride target leads to optical emissions in the (at least) visible and infrared regions of the spectrum. Researchers describe y details of the photodetachment source, and present spectra of the neutral and ion glows in the wavelength range 250 to 850 nm (for O(-)) and 600 to 850 nm (for O), and discuss the variability of the emissions for incident energies between 4 and 40 eV.

Chutjian, A.↗

NASA NTRS1991

Vacuum deposited optical coatings experiment (AO 138-4)

The aim of this experiment was to test the optical behavior of 20 components and coatings subjected to space exposure. Most of them are commonly used for their reflective or transmittive properties in spaceborne optics. They consist in several kind of metallic and dielectric mirrors designed for the 0.12 to 10 microns spectrum, UV, and NIR bandpass filters, visible, and IR antireflecting coatings, visible/IR dichroic beam splitters, and visible beam splitter. The coatings were deposited on various substrates such as glasses, germanium, magnesium fluoride, quartz, zinc selenide, and kanigened aluminum. Several coating materials were used such as Al, Ag, Au, MgF2, LaF3, ThF3, ThF4, SiO2, TiO2, ZrO2, Al2O3, MgO, Ge, and ZnSe. Five samples of each component were manufactured. Two flight samples were mounted in such a way that one was directly exposed to space and the other looking backwards. The same arrangement was used for the spare samples stored on ground in a box identical to the flight one and they were kept under vacuum during the LDEF mission. Finally, one set of reference components was stocked in a sealed box under a dry nitrogen atmosphere. By comparing the preflight and postflight optical performances of the five samples of each component, it is possible to detect the degradations due to the space exposure.

Charlier, Jean↗

NASA NTRS1990

Experimental investigations of low-energy (4-40 eV) collisions of O-(2P) ions and O(3P) atoms with surfaces

Using a newly-developed, magnetically confined source, low-energy, ground state oxygen negative ions and neutral atoms are generated. The energy range is variable, and atom and neutrals have been generated at energies varying from 2 eV to 40 eV and higher. It was found that the interaction of these low-energy species with a solid magnesium fluoride target leads to optical emissions in the (at least) visible and infrared regions of the spectrum. Researchers describe y details of the photodetachment source, and present spectra of the neutral and ion glows in the wavelength range 250 to 850 nm (for O/-/) and 600 to 850 nm (for O), and discuss the variability of the emissions for incident energies between 4 and 40 eV.

Orient, O. J.↗