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  • 1
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    Retrieval of monthly rainfall indices from microwave radiometric measurements using probability distribution functions (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: An algorithm for the estimation of monthly rain totals for 5 deg cells over the ocean from histograms of SSM/I brightness temperatures has been developed. There are three novel features to this algorithm. First, it uses knowledge of the form of the rainfall intensity probability density function to augment the measurements. Second, a linear combination of the 19.35 and 22.235 GHz channels has been employed to reduce the impact of variability of water vapor. Third, an objective technique has been developed to estimate the rain layer thickness from the 19.35- and 22.235-GHz brightness temperature histograms. Comparison with climatologies and the GATE radar observations suggest that the estimates are reasonable in spite of not having a beam-filling correction. By-products of the retrievals indicate that the SSM/I instrument noise level and calibration stability are quite good.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Atmospheric and Oceanic Technology (ISSN 0739-0572); 8; 118-136
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  • 2
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    Linear stability of free planetary waves in the presence of radiative-photochemical feedbacks (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The diabatic effects of Newtonian cooling and ozone-dynamics interaction on the linear stability of free planetary waves in the atmosphere have been studied using a simple beta-plane model. The model couples radiative transfer, ozone advection, and ozone photochemistry with the quasi-geostrophic dynamical circulation. An analytical expression is derived which demonstrates the following: (1) the influence of meridional ozone advection on wave growth or decay depends on the wave and basic state vertical structures; and (2) photochemically accelerated cooling, which predominates in the upper stratosphere, augments the Newtonian cooling rate and is stabilizing. Attention is also given to the 1D linear stability problem which is numerically solved for a Charney basic state and for zonal mean basic states. It is shown that ozone heating generated by ozone-dynamics interaction in the stratosphere can reduce (enhance) the damping rates due to Newtonian cooling by as much as 50 percent for planetary waves of large vertical scale and maximum amplitude in the stratosphere.
    Keywords: GEOPHYSICS
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 48; 1837-185
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  • 3
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    Terrestrial weathering of Antarctic stone meteorites - Formation of Mg-carbonates on ordinary chondrites (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results are presented on the mineralogy, chemistry, and origin of white efflorescences on the surface of Lewis Cliff (Antarctica) 85320 (H5) chondrite (LEW 85320). Particular attention is given to determining the sources of the cations and anions of the evaporite, in order to establish the relative importance of the meteoritic element distribution and terrestrial contamination in the evaporite formation during the weathering process. The data on Na, K, Ca, and Rb abundances in efflorescence from LEW 85320 suggest that cations in evaporite minerals on Antarctic meteorites are not the products of contamination by terrestrial (marine) salts. It is suggested that the Mg in efflorescence on LEW 85320 originated from weathering of meteoritic olivine.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 55; 67-76
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  • 4
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    The RAPT control method for nonlinear systems (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Rapid Advancement Preview Tracking (RAPT) control method uses both a nonlinear system model and a linearized system model to provide a form of feedback/preview control for nonlinear systems. It uses measurements of the states to calculate the current preview control signal from a local linearization of the state equations, and then iteratively calculates a perturbation correction for that control using the nonlinear equations. The corrected control signal is then applied to the system, driving the end-effector to the next position along a specified trajectory. Computer simulations of tracking control for two-link planar manipulators indicate that this algorithm may be fast enough for real-time control.
    Keywords: CYBERNETICS
    Type: ASME, Transactions, Journal of Dynamic Systems, Measurement, and Control (ISSN 0022-0434); 113; 736-741
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  • 5
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    Ultrasonic detection and identification of fabrication defects in composites (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Methods for deliberate fabrication of porosity into carbon/epoxy composite panels and the influence of three-dimensional stitching on the detection of porosity were investigated. Two methods of introducing porosity were investigated. Porosity was simulated by inclusion of glass microspheres, and a more realistic form of porosity was introduced by using low pressure during consolidation. The panels were ultrasonically scanned and the frequency slope of the ultrasonic attenuation coefficient was used to evaluate the two forms of porosity. The influence of stitching on the detection of porosity was studied using panels which were resin transfer molded from stitched plies of knitted carbon fabric and epoxy resin.
    Keywords: COMPOSITE MATERIALS
    Type: First NASA Advanced Composites Technology Conference, Part 2; p 705-720
    Format: application/pdf
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  • 6
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    Spaceborne radar measurement of wind velocity over the ocean - An overview of the NSCAT scatterometer system (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Scatterometry and scatterometer design issues are reviewed. The design of the NASA Scatterometer (NSCAT) to be flown on the Japanese ADEOS mission is presented. Building on Seasat experience, the NSCAT system includes several enhancements, such as three antenna azimuths in each of two swaths, and an onboard digital Doppler processor to allow backscatter measurements to be colocated everywhere within the orbit. These enhancements will greatly increase the quality of the NSCAT wind data. The ground processing of data is discussed, and scatterometers of the next decade are briefly described.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: IEEE, Proceedings (ISSN 0018-9219); 79; 850-866
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  • 7
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    An experimental apparatus for measuring surface resistance in the submillimeter-wavelength region (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A method for measuring the surface electrical resistance of small metallic samples at submillimeter wavelengths is presented which employs a qausi-optical hemispherical resonator fed by an optically pumped far-infrared laser. The small beam size at the sample, which serves as a plane mirror, allows measurements on samples with widths as small as 5 mm. The quality factor is high, and surface resistance losses are readily measurable.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 62; 2480-248
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  • 8
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    Wind-tunnel and flight tests of a delta-wing remotely piloted vehicle (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 728-734
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  • 9
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    Optical performance of exposed solar cell covers (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: The characterization results of samples flown on the Long Duration Exposure Facility (LDEF) are discussed. These samples included both coated and uncoated fused silica and ceria glass substrates used in the manufacture of solar cell covers. The coatings comprised a single-layer magnesium fluoride antireflection coating and an all-dielectric high-reflector multilayer coating centered at 350 nm. Samples were mounted on both the leading and trailing surfaces of the LDEF for exposure to the environment of space. The optical properties of the coatings will be compared to control samples which were stored on the ground during the LDEF Mission. Results of Auger Electron Spectroscopy and Rutherford Backscatter Spectroscopy measurements made on several of the coatings are presented to explain the effects of space on the chemical composition of the coatings.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA, Langley Research Center, First LDEF Post-Retrieval Symposium Abstracts; p 106
    Format: text
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  • 10
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    Infiltration/cure modeling of resin transfer molded composite materials using advanced fiber architectures (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A model was developed which can be used to simulate infiltration and cure of textile composites by resin transfer molding. Fabric preforms were resin infiltrated and cured using model generated optimized one-step infiltration/cure protocols. Frequency dependent electromagnetic sensing (FDEMS) was used to monitor in situ resin infiltration and cure during processing. FDEMS measurements of infiltration time, resin viscosity, and resin degree of cure agreed well with values predicted by the simulation model. Textile composites fabricated using a one-step infiltration/cure procedure were uniformly resin impregnated and void free. Fiber volume fraction measurements by the resin digestion method compared well with values predicted using the model.
    Keywords: COMPOSITE MATERIALS
    Type: First NASA Advanced Composites Technology Conference, Part 2; p 425-441
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