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  • Other Sources  (8)
  • 1990-1994  (8)
  • 1
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    Modulation for terrestrial broadcasting of digital HDTV (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The digital modulation methods used by the DigiCipher, DSC-HDTV, ADTV, and ATVA-P digital high-definition television (HDTV) systems are discussed. Three of the systems use a quadrature amplitude modulation method, and the fourth uses a vestigial sideband modulation method. The channel equalization and spectrum sharing of the digital HDTV systems is discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Broadcasting (ISSN 0018-9316); 37; 141-144
    Format: text
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  • 2
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    Visual cueing considerations in Nap-of-the-Earth helicopter flight head-slaved helmet-mounted displays (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The pilot's ability to derive Control-Oriented Visual Field Information from teleoperated Helmet-Mounted displays in Nap-of-the-Earth flight, is investigated. The visual field with these types of displays, commonly used in Apache and Cobra helicopter night operations, originates from a relatively narrow field-of-view Forward Looking Infrared Radiation Camera, gimbal-mounted at the nose of the aircraft and slaved to the pilot's line-of-sight, in order to obtain a wide-angle field-of-regard. Pilots have encountered considerable difficulties in controlling the aircraft by these devices. Experimental simulator results presented here indicate that part of these difficulties can be attributed to head/camera slaving system phase lags and errors. In the presence of voluntary head rotation, these slaving system imperfections are shown to impair the Control-Oriented Visual Field Information vital in vehicular control, such as the perception of the anticipated flight path or the vehicle yaw rate. Since, in the presence of slaving system imperfections, the pilot will tend to minimize head rotation, the full wide-angle field-of-regard of the line-of-sight slaved Helmet-Mounted Display, is not always fully utilized.
    Keywords: MAN/SYSTEM TECHNOLOGY AND LIFE SUPPORT
    Type: Piloting Vertical Flight Aircraft: A Conference on Flying Qualities and Human Factors; p 315-327
    Format: application/pdf
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  • 3
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    The response of C1O radical concentrations to variations in NO2 radical concentrations in the lower stratosphere (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The respose of ClO concentrations to changes in NO2 concentrations has been inferred from simultaneous observations of (ClO), (NO), (NO2) and (O3) in the midlatitude lower stratosphere. This analysis demonstrates that (ClO) is inversely correlated with (NO2), consistent with formation and photolysis of (ClONO2). A factor of ten range in the concentration if NO2 was sampled (0.1 to 1 x 10(exp 9) mol/cu cm), with a comparable range in the ratio of (ClO) to total available inorganic chlorine (1% less than or equal to (ClO)/(Cl(sub y)) less than or equal to 5%. This analysis leads to an estimate of (ClONO2)/(Cl(sub y)) = 0.12 (x/2), in the mid-latitude, lower-stratospheric air masses sampled.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 23; p. 2543-2546
    Format: text
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  • 4
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    The Diurnal Variation of Hydrogen, Nitrogen, and Chlorine Radicals: Implications for the Heterogeneous Production of HNO2 (1994)
    In:  CASI
    Details
    Publication Date: 2019-08-17
    Description: In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained through sunrise and sunset in the lower stratosphere during SPADE are compared to results from a photochemical model constrained by observed concentrations of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N205 on sulfate aerosols agree with measured concentrations of NO, NO2, and ClO throughout the day, but fail to account for high concentrations of OH and H02 observed near sunrise and sunset. The morning burst of [OH] and [HO2] coincides with the rise of [NO] from photolysis of N02, suggesting a new source of HO, that photolyzes in the near UV (350 to 400 nm) spectral region. A model that allows for the heterogeneous production of HN02 results in an excellent simulation of the diurnal variations of [OH] and [HO2].
    Keywords: Geophysics
    Type: NASA-CR-204900 , Paper-94-GL-02782 , NAS 1.26:204900 , Geophysical Research Letters (ISSN 0094-8534); 21; 23; 2551-2554
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  • 5
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    Visual field information in Nap-of-the-Earth flight by teleoperated Helmet-Mounted displays (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The human ability to derive Control-Oriented Visual Field Information from teleoperated Helmet-Mounted displays in Nap-of-the-Earth flight, is investigated. The visual field with these types of displays originates from a Forward Looking Infrared Radiation Camera, gimbal-mounted at the front of the aircraft and slaved to the pilot's line-of-sight, to obtain wide-angle visual coverage. Although these displays are proved to be effective in Apache and Cobra helicopter night operations, they demand very high pilot proficiency and work load. Experimental work presented in the paper has shown that part of the difficulties encountered in vehicular control by means of these displays can be attributed to the narrow viewing aperture and head/camera slaving system phase lags. Both these shortcomings will impair visuo-vestibular coordination, when voluntary head rotation is present. This might result in errors in estimating the Control-Oriented Visual Field Information vital in vehicular control, such as the vehicle yaw rate or the anticipated flight path, or might even lead to visuo-vestibular conflicts (motion sickness). Since, under these conditions, the pilot will tend to minimize head rotation, the full wide-angle coverage of the Helmet-Mounted Display, provided by the line-of-sight slaving system, is not always fully utilized.
    Keywords: AIRCRAFT INSTRUMENTATION
    Type: In: Large-screen-projection, avionic, and helmet-mounted displays; Proceedings of the Meeting, San Jose, CA, Feb. 26-28, 1991 (A93-26881 09-54); p. 132-153.
    Format: text
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  • 6
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    The Response of ClO Radical Concentrations to Variations in NO2 Radical Concentrations in the Lower Stratosphere (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The response of ClO concentrations to changes in NO2 concentrations has been inferred from simultaneous observations of [ClO], [NO], [NO2] and [O3] in the mid-latitude lower stratosphere. This analysis demonstrates that [ClO] is inversely correlated with [NO2], consistent with formation and photolysis of [ClONO2]. A factor of ten range in the concentration of NO2 was sampled (0.1 to 1 x 10(exp 9) mol/cc), with a comparable range in the ratio of [ClO] to total available inorganic chlorine (1% 〈= [ClO]/[Cl(sub y)] 〈= 5%). This analysis leads to an estimate of [ClONO2]/[Cl(sub y)] = 0.12 (x/divided by 2), in the mid-latitude, lower-stratospheric air masses sampled.
    Keywords: Environment Pollution
    Type: Paper-94GL02373 , Geophysical Research Letters (ISSN 0094-8534); 21; 23; 2543-2546
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  • 7
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    Flight-path estimation in passive low-altitude flight by visual cues (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: A series of experiments was conducted, in which subjects had to estimate the flight path while passively being flown in straight or in curved motion over several types of nominally flat, textured terrain. Three computer-generated terrain types were investigated: (1) a random 'pole' field, (2) a flat field consisting of random rectangular patches, and (3) a field of random parallelepipeds. Experimental parameters were the velocity-to-height (V/h) ratio, the viewing distance, and the terrain type. Furthermore, the effect of obscuring parts of the visual field was investigated. Assumptions were made about the basic visual-field information by analyzing the pattern of line-of-sight (LOS) rate vectors in the visual field. The experimental results support these assumptions and show that, for both a straight as well as a curved flight path, the estimation accuracy and estimation times improve with the V/h ratio. Error scores for the curved flight path are found to be about 3 deg in visual angle higher than for the straight flight path, and the sensitivity to the V/h ratio is found to be considerably larger. For the straight motion, the flight path could be estimated successfully from local areas in the far field. Curved flight-path estimates have to rely on the entire LOS rate pattern.
    Keywords: BEHAVIORAL SCIENCES
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 16; 2; p. 363-370.
    Format: text
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  • 8
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    The Distribution of Hydrogen, Nitrogen, and Chlorine Radicals in the Lower Stratosphere: Implications for Changes in O3 due to Emission of NO(y) from Supersonic Aircraft (1994)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained in the lower stratosphere during the Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE) are compared to results from a photochemical model that assimilates measurements of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N2O5 agree well with measured concentrations of NO and ClO, but concentrations of HO2 and OH are underestimated by 10 to 25%, concentrations of NO2 are overestimated by 10 to 30%, and concentrations of HCl are overestimated by a factor of 2. Discrepancies for [OH] and [HO2] are reduced if we allow for higher yields of O(sup 1)D) from 03 photolysis and for heterogeneous production of HNO2. The data suggest more efficient catalytic removal of O3 by hydrogen and halogen radicals relative to nitrogen oxide radicals than predicted by models using recommended rates and cross sections. Increases in [O3] in the lower stratosphere may be larger in response to inputs of NO(sub y) from supersonic aircraft than estimated by current assessment models.
    Keywords: Geophysics
    Type: NASA-CR-204901 , Paper-94GL02781 , NAS 1.26:204901 , Geophysical Research Letters (ISSN 0094-8534); 21; 23; 2547-2550
    Format: application/pdf
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