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  • 1
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    Polarimetric and multifrequency SAR signatures of wet snow (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: C-, L-, and P-band polarimetric signatures of wet snow surfaces have been analyzed, based on airborne synthetic aperture radar (AIRSAR) surveys of an Alpine test site. The importance of surface roughness is evident in the C- and L-band signatures, whereas the diffuse scattering contribution by internal inhomogeneities in the snowpack increases from the C- to the P-band at incidence angles below 50 deg due to increasing penetration.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 2 (A93-47551 20-43); p. 1658-1660.
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  • 2
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    Reflectance and transmittance of snow at high spectral resolution (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A radiative-transfer model for the bidirectional reflectance-distribution function (BRDF) shows that snow is moderately anisotropic in the NIR 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 and the transmittance for a variety of snow conditions were made throughout the winter and spring seasons with an SE-590 spectroradiometer, for wavelengths from 0.38 to 1.11 microns. Coincident with these, the surface grain properties were analyzed by stereological methods. A sphere with the same surface-to-volume ratio as the ice grains is used as the equivalent sphere.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
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  • 3
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    Snow property measurements correlative to microwave emission at 35 GHz (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    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: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); GE-25; 751-757
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  • 4
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    Snow and glacier mapping with polarimetric SAR (1991)
    In:  Other Sources
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    Publication Date: 2013-08-29
    Description: The objective of this study was to examine the capability of mapping snow and glaciers in alpine regions using synthetic aperture radar (SAR) imagery when topographic information is not available. The topographic effects on the received power for a resolution cell can be explained by the change in illumination area and incidence angle in a slant-rante representation of SAR imagery. The specific polarization signatures and phase difference between HH and VV components are relatively independent of the illuminated are, and the incidence angle has only a small effect on these parameters. They provide a suitable measurement data set for snow and glacier mapping in a high-relief area. The results show that the C-band images of the enhancement factor, the phase difference between HH and VV scattering components, and the normalized cross product of VV scattering elements provide the capability to discriminate among snow with different wetnesses, glaciers, and rocky regions.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Proceedings of the Third Airborne Synthetic Aperture Radar (AIRSAR) Workshop; p 78-87
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  • 5
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    Satellite Repair Program (1991)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: NASA-Goddard's Satellite Repair Program counts among its major achievements the successful use of welding in servicing equipment employed in the Flight Support System (FSS) structures addressed by the the Solar Maximum Repair Mission of 1984. The FSS berthing and positioning ring will again be employed with the Space Shuttle for the anticipated upgrading of the Hubble Space Telescope; the Explorer Platform (EP) mission will also use the FSS during the planned on-orbit exchange of the EUV Explorer payload for an X-ray Timing Explorer payload. The EP, to which attention is presently given, is the first spacecraft designed to be entirely serviceable by intravehicular activity or EVA.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: Welding in Space and the Construction of Space Vehicles by Welding; Sept. 24-26, 1991; New Carrollton, MD; United States
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  • 6
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    View Angle Effects on MODIS Snow Mapping in Forests (2012)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: Binary snow maps and fractional snow cover data are provided routinely from MODIS (Moderate Resolution Imaging Spectroradiometer). This paper investigates how the wide observation angles of MODIS influence the current snow mapping algorithm in forested areas. Theoretical modeling results indicate that large view zenith angles (VZA) can lead to underestimation of fractional snow cover (FSC) by reducing the amount of the ground surface that is viewable through forest canopies, and by increasing uncertainties during the gridding of MODIS data. At the end of the MODIS scan line, the total modeled error can be as much as 50% for FSC. Empirical analysis of MODIS/Terra snow products in four forest sites shows high fluctuation in FSC estimates on consecutive days. In addition, the normalized difference snow index (NDSI) values, which are the primary input to the MODIS snow mapping algorithms, decrease as VZA increases at the site level. At the pixel level, NDSI values have higher variances, and are correlated with the normalized difference vegetation index (NDVI) in snow covered forests. These findings are consistent with our modeled results, and imply that consideration of view angle effects could improve MODIS snow monitoring in forested areas.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC-E-DAA-TN9223 , Remote Sensing of Environment ; 118; 50-59
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  • 7
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    Space Shuttle Orbiter Structures and Mechanisms (2011)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: The Space Shuttle Orbiter has performed exceptionally well over its 30 years of flight experience. Among the many factors behind this success were robust, yet carefully monitored, structural and mechanical systems. From highlighting key aspects of the design to illustrating lessons learned from the operation of this complex system, this paper will attempt to educate the reader on why some subsystems operated flawlessly and why specific vulnerabilities were exposed in others. Specific areas to be covered will be the following: high level configuration overview, primary and secondary structure, mechanical systems ranging from landing gear to the docking system, and windows.
    Keywords: Spacecraft Design, Testing and Performance
    Type: JSC-CN-24473 , AIAA Space 2011 Conference and Convention: Shuttle Legacy Track; Oct 26, 2011 - Oct 29, 2011; Long Beach, CA; United States
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  • 8
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    Stereological characterization of dry alpine snow for microwave remote sensing (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A persistent problem in investigations of electromagnetic properties of snow, from reflectance at visible wavelengths to emission and backscattering in the microwave, has been the proper characterization of the snow's physical properties. It is suggested that the granular and laminar structure of snow can be measured in its aggregated state by stereology performed on sections prepared from snow specimens, and that these kinds of measurements can be incorporated into models of the electromagnetic properties. With careful sampling, anisotropy in the snow microstructure at various scales can be quantified. It is shown how stereological parameters can be averaged over orientation and optical depth for radiative transfer modeling.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Advances in Space Research (ISSN 0273-1177); 9; 1 19
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  • 9
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    Mechanical Systems (2002)
    In:  CASI
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    Publication Date: 2019-08-13
    Description: The presentation provides an overview of requirement and interpretation letters, mechanical systems safety interpretation letter, design and verification provisions, and mechanical systems verification plan.
    Keywords: Engineering (General)
    Type: JSC-CN-7576 , Joint ESA-NASA Space Flight Safety Conference: "Safety through Partnership"; Jun 11, 2002 - Jun 14, 2002; Noordwijk; Netherlands
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  • 10
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    Research relative to angular distribution of snow reflectance/snow cover characterization and microwave emission (1987)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Remote sensing has been applied in recent years to monitoring snow cover properties for applications in hydrologic and energy balance modeling. In addition, snow cover has been recently shown to exert a considerable local influence on weather variables. Of particular importance is the potential of sensors to provide data on the physical properties of snow with high spatial and temporal resolution. Visible and near-infrared measurements of upwelling radiance can be used to infer near-surface properties through the calculation of albedo. Microwave signals usually come from deeper within the snow pack and thus provide depth-integrated information, which can be measured through clouds and does not relay on solar illumination.Fundamental studies examining the influence of snow properties on signals from various parts of the electromagnetic spectrum continue in part because of the promise of new remote sensors with higher spectral and spatial accuracy. Information in the visible and near-infrared parts of the spectrum comprise nearly all available data with high spatial resolution. Current passive microwave sensors have poor spatial resolution and the data are problematic where the scenes consist of mixed landscape features, but they offer timely observations that are independent of cloud cover and solar illumination.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NASA-CR-182733 , NAS 1.26:182733
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