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  • 1
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    Influence of atmospheric aerosols and desert reflectance properties on satellite radiance measurements (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The influence of surface bidirectional reflectance factors, including shadowing, and of atmospheric aerosol variability are modeled for their effects on the remote sensing of desert targets from space in the 0.7-micron region at high spatial resolution. The white sand reflectance data of Salomonson (1968) are used as the basis for the simulation. The effects of the surface bi-directional reflectance and atmospheric aerosol on the nadir-normalized reflectance measured at the satellite are discussed individually and jointly. The net influence of these two factors is shown to depend on the magnitude of other parameters, such as the surface reflectance and solar zenith angle.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: International Journal of Remote Sensing (ISSN 0143-1161); 13; 16; p. 3105-3126.
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  • 2
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    Snow property measurements correlative to microwave emission at 35 GHz (1986)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: Snow microstructure, measured by plane section analysis, and snow wetness, measured by the dilution method, are used to calculate input parameters for a microwave emission model that uses the radiative transfer method. The scattering and absorbing properties are calculated by Mie theory. The effects of different equivalent sphere conversions, adjustments for near-field interference, and different snow wetness characterizations are compared for various snow conditions. The concentric shell geometry of liquid water in snow yields higher emissivities and better model results than the separate-sphere configuration for liquid water contents greater than 0.05, while at lower liquid water contents the separate-sphere treatment gives better results.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: ESA Proceedings of the 1986 International Geoscience and Remote Sensing Symposium (IGARSS '86) on Remote Sensing: Today's Solutions for Tomorrow's Information Needs, Volume 2; p 915-920
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  • 3
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    The spectral bidirectional reflectance of snow (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: A radiative transfer model for the bidirectional reflectance-distribution function (BRDF) shows that snow is moderately anisotropic in the near-infrared wavelengths. Although the directional-hemispherical albedo of snow decreases as the grains become larger, the forward scattering also increases, with the result that the illumination and viewing geometry must be considered when interpreting physical properties of the surface layer of the snow pack from remote sensing data. Measurements of the BRDF for a variety of snow conditions were made throughout the winter and spring seasons with a spectroradiometer, for wavelengths from 0.38 to 1.11 microns. Coincident with these the surface grain properties were analyzed by stereological methods. The data show that Mie scattering calculations using an equivalent spherical radius match the directional-hemispherical reflectance, but the BRDF usually shows a small peak in the backscattered direction that would not occur from spherical grains. The sphere with the same surface-to-volume ratio as the ice grains is used as the equivalent sphere.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: ESA, Proceedings of the 4th International Colloquium on Spectral Signatures in Remote Sensing; p 87-92
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  • 4
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    The observations of the X-ray source HZ Herculis/Hercules X-1 (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The results of a campaign of monitoring HZ Her with the IUE satellite are presented. The spectrum and light variation outside of eclipse are consistent with the Milgrom and Salpeter model for emission from the X-ray heated photosphere of the primary. Near eclipse there is UV flux in excess of the prediction of the heated photosphere model, which shows significant 35 day variations and is consistent with an origin in a precessing disk, as described by Gerend and Boynton. The spectrum shows the strong emission lines of N V and C IV, which generally vary in the sense of the continuum. The N V/C IV ratio is greater than 2 near orbital phase 0.5 and approaches unity near eclipse. It is suggested that these emission lines are optically thick and arise from both the heated photosphere and the accretion disk.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 237
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  • 5
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    IUE observations of X-ray sources - HD153919 /4U1700-37/, HDE226868 /Cyg X-1/, HZ Her /Her X-1/ (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The first UV spectroscopic measurements of binary X-ray sources with IUE show highly variable emission from a photoionized plasma in the object HZ Her, and give evidence for localized circumsystem material in the binary source Cygnus X-1. In addition, a substantial stellar wind is found in one of the brightest identified X-ray sources HD153919. This system may be surrounded by an extensive H II region unusual in its content of high excitation ion species.
    Keywords: ASTROPHYSICS
    Type: Nature; 275; Oct. 5
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  • 6
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    LANDSAT-D investigations in snow hydrology (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Work undertaken during the contract and its results are described. Many of the results from this investigation are available in journal or conference proceedings literature - published, accepted for publication, or submitted for publication. For these the reference and the abstract are given. Those results that have not yet been submitted separately for publication are described in detail. Accomplishments during the contract period are summarized as follows: (1) analysis of the snow reflectance characteristics of the LANDSAT Thematic Mapper, including spectral suitability, dynamic range, and spectral resolution; (2) development of a variety of atmospheric models for use with LANDSAT Thematic Mapper data. These include a simple but fast two-stream approximation for inhomogeneous atmospheres over irregular surfaces, and a doubling model for calculation of the angular distribution of spectral radiance at any level in an plane-parallel atmosphere; (3) incorporation of digital elevation data into the atmospheric models and into the analysis of the satellite data; and (4) textural analysis of the spatial distribution of snow cover.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: E86-10007 , NASA-CR-176379 , NAS 1.26:176379
    Format: application/pdf
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  • 7
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    Spectral reflectances of natural targets for use in remote sensing studies (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A collection of spectral reflectances of 156 natural targets is presented in a uniform format. For each target both a graphical plot and a digital tabulation of reflectance is given. The data were taken from the literature and include laboratory, field, and aircraft measurements. A discussion of the different measurements of reflectance is given, along with the changes in apparent reflectance when targets are viewed through the atmosphere. The salient features of the reflectance curves of common target types are presented and discussed.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NASA-RP-1139 , L-15920 , NAS 1.61:1139
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  • 8
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    Constraints on the inclination and masses of the HDE 226868/Cygnus X-1 system from the observations (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Analyses of two high-dispersions IUE spectra of HDE 226868 (the optical counterpart of Cygnus X-1) are combined with studies of low-dispersion IUE spectra to provide a more accurate determination of the variation of C IV stellar wind absorption as a function of orbital phase. By incorporating these observational results into an analysis of the structure of the X-ray ionization cavity in the stellar wind, it is found that the orbital inclination must lie between 36 and 67 deg, leading to a mass for the compact object between 5.7 and 11.2 solar masses.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 270; July 15
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  • 9
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    Simultaneous ultraviolet, optical, and X-ray observations of the X-ray source Vela X-1 /HD 77581/ (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: UV spectra (obtained by the IUE) of HD 77581, associated with the binary X-ray source Vela X-1, show a spectrum typical of an early B-type supergiant. However, the P Cygni profiles of strong resonance lines show substantial variations with orbital phase. These variations can be ascribed to the changing ionization state in the stellar wind caused by the X-ray emitting companion. X-ray and spectroscopic and photometric optical observations, simultaneous with the IUE observations, indicate behavior consistent with previous epochs.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 238
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  • 10
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    Chromospheres of the active dwarf binaries EQ Pegasi and Xi Bootis (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Ultraviolet spectroscopic measurements of the M dwarf binary EQ Peg and the G8 V star Xi Boo A have been made with the International Ultraviolet Explorer satellite. High-temperature emission lines (N V, C IV, Si IV) are present with similar strengths in both stars. The surface fluxes of chromospheric and transition-region lines are enhanced relative to those of normal main-sequence stars and are comparable to those observed in solar active regions. If inhomogeneities are present, the surface fluxes may be markedly higher than the derived values. It is likely that the emission observed from EQ Peg was not the result of major flare activity; however, the quiescent radiative losses observed in the ultraviolet are comparable to the time-averaged optical flare losses. The similarity of the line emissions of active dwarfs of diverse spectral types suggests that the character of the transition region is independent of the stellar effective temperature.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 233
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