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  • 1
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    Plans to improve the experimental limit in the comparison of the east-west and west-east one-way light propagation times on the rotating earth (1993)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The preceding paper describes the results so far (interrupted in the Spring of 1989 because of lack of funds) of an experiment comparing the one-way light propagation times on the surface of the rotating Earth. For the 20 Km path length component in the East-West direction the predicted difference between the opposite sense propagation times would be 160 ps, if the approximately 360 Km/s surface speed of the Earth gives effective light speeds of 3 x 10(exp 8) m/s +/- 360 m/s. This could lead to a prediction of the difference between the clock transport and the light pulse synchronization methods described in the preceding paper: delta(T) = 0.5 (160) = 80 ps. The current upper bound of approximately 100 ps for delta(T) is limited by poorly understood systematic errors. The most important seems to be intensity-dependent time delays in the remote light pulse avalanche photo-diode detector. This will be replaced by a continuously operating circular scan streak camera having single photon sensitivity and a time resolution of approximately 5 ps. (This camera has recently been developed by the Xian Institute of Optics and Precision Mechanics in the P.R.C.). Better isolation from shocks and vibration for the Sigma-Tau hydrogen maser during transport will be provided. It is hoped that delta(T) is less than 20 ps can be achieved.
    Keywords: OPTICS
    Type: NASA. Goddard Space Flight Center, The 24th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting; p 105-112
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  • 2
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    Large format, high resolution images sensors (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The performance requirements for scientific-quality CCDs are discussed, focusing on the design of two devices, and the progress toward achieving the desired performance is discussed. These devices are intended for rear-illuminated applications and have 512 x 512 and 2048 x 2048 pixel formats. The thinned 10 to 20 micron thick Si membrane is fully supported by a unique glass ceramic substrate. Quantum efficiencies of greater than 70 percent at 700 nm and greater than 40 percent at wavelengths less than 400 nm have been measured on a test device. Dark currents as low as 6 pA/sq cm also have been measured recently.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Optical Engineering (ISSN 0091-3286); 26; 837-843
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  • 3
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    Radio scintillations during occultations by turbulent planetary atmospheres (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The radio occultation experiment which uses the radio link between the earth and spacecraft passing behind planets has proven to be an important method for remote sensing turbulence in planetary atmospheres. The effects of defocusing and anisotropic irregularities on the turbulence-induced fluctuations of the radio occultation signal are examined. Rytov's method along with geometrical optics is employed to study the frequency spectra and coherences of the log amplitude and phase fluctuations of spherical waves operating at one as well as two frequencies. Comparison with the Mariner 5 2.3-GHz measurements shows good agreement with the theoretical results.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: Radio Science; 15; May-June
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  • 4
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    Probing the solar wind with radio measurements of the second moment field (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The dependence of spectral broadening on anisotropic electron-density irregularities and velocity fluctuations in the solar wind is investigated on the basis of results for a second moment mutual coherence function obtained by a parabolic-equation method. It is found that although anisotropic irregularities and wind-velocity fluctuations decrease the bandwidth of the spectrum relative to that for isotropic irregularities and no velocity fluctuations, the shape of the spectrum remains unchanged. Examination of the frequency dependence and shape of a computed angular spectrum indicates that the electron-density spectrum is consistent with a power law having a spectral index close to the value appropriate for the Kolmogorov spectrum. It is proposed that multiple-station observations of some total field be employed to measure the solar wind.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 218
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  • 5
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    Scintillation estimates for a Jupiter entry probe: Phase 1 (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A model of the electron density irregularities in the Jovian ionosphere is constructed based on a preliminary interpretation of the Pioneer 10 Jovian ionospheric scintillations. The ionospheric irregularities exist over an altitude range of 3000 km. The structure constant c sub n of refractive index fluctuations is constant throughout this altitude range. The spatial wavenumber spectrum of the electron density irregularities follows the Kolmogorov spectrum and the outer scale size is greater than 6 km. Estimates of scintillation for a Jovian entry probe based on this model indicate that it is small at S-band but could be substantial at 4000 MHz. The temporal frequency spectrum of the log-amplitude fluctuation is less than 1 Hz and is consequently rather narrow.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-145769 , JPL-TM-33-745
    Format: application/pdf
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  • 6
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    Measurements of the magnetic field orientation in the Jovian ionosphere deduced from Pioneer 10 and 11 scintillation observations (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: In this paper the S band scintillations observed during the Pioneer 10 and 11 occultation measurements of Jupiter are analyzed. It is found that while the electron density irregularities are isotropic in the collision-dominated lower ionosphere, they are anisotropic in the upper ionosphere because of alignment along the magnetic field. By using Rytov's approximation the frequency spectrum of the log-amplitude scintillations is derived for a wave propagating in an anisotropic turbulent medium. It is shown that the spectrum depends to a large extent on the direction of anisotropy and is therefore useful for measuring the orientation of the magnetic field in regions that have not yet been probed by direct measurements. This new technique is applied to the Pioneer 10 and 11 observations, and is used to deduce the first measurements of magnetic field orientation in the ionosphere of Jupiter.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 83; Nov. 1
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  • 7
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    HF Doppler and VHF radar observations of upper atmospheric disturbances caused by weak cold front during winter time (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The simultaneous use of the Taiwan VHF radar and the HF Doppler sounder for remote measurement of three-dimensional winds, gravity waves, and density perturbations at mesospheric and thermospheric heights is demonstrated. A special event of atmospheric disturbances caused by propagating gravity waves excited by weak convective motions in winter time were investigated. The three-dimensional wind velocities at different heights were determined, and the frequency, horizontal wavelength, vertical wavelength, and phase velocity of the gravity waves were measured. The subtropical, low-latitude site makes the VHF radar and HF Doppler array systems unique, and the observations especially valuable for space projects dealing with low-latitude atmosphere.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: AIAA PAPER 90-0483
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  • 8
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    Structure of density fluctuations near the sun deduced from Pioneer-6 spectral broadening measurements (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Spectral broadening of monochromatic radio waves by density fluctuations near the sun is analyzed using the parabolic equation method. Application of the analysis to the 1968 Pioneer-6 spectral broadening observations yields indirect measurements of the density spectrum within 14 solar radii of the sun. For spatial wavenumbers of at least 0.0084 inverse km, the three-dimensional density spectrum is found to be close to the Kolmogorov spectrum (power law with spectral index of 11/3) and is consistent with interplanetary-scintillation and in situ spacecraft measurements farther from the sun. The magnitude of the density spectrum increases, but its shape remains the same during 'solar events' marked by increases in bandwidth.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; 210; Dec. 1
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  • 9
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    Measurements of large-scale density fluctuations in the solar wind using dual-frequency phase scintillations (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: It is demonstrated that phase-difference scintillations measured with a coherent dual-frequency radio system such as that on Mariner 10 can be used to study the structure of density fluctuations in the solar wind covering a wider range of scale sizes than has ever been possible before. The Mariner 10 observations at solar elongations of 11.5 and 12.6 deg show that the density spectrum in the frequency range from 0.0001 to 0.5 Hz, which corresponds to the spatial wavenumber range of 2 millionths to 0.001 inverse km if the solar wind velocity is assumed to be 350 km/s, is approximately power-law and close to Kolmogorov (spectral index of 11/3). The results are consistent with direct spacecraft observations near earth and provide strong evidence that the density fluctuations are produced by turbulence. The potential and benefits of future extensive measurements are also discussed.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; 210; Dec. 1
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  • 10
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    Measurements of electron density irregularities in the ionosphere of Jupiter by Pioneer 10 (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: It is demonstrated that when the frequency spectrum of log amplitude fluctuations is used, the radio-occultation experiment is a powerful tool for detecting, identifying, and studying ionospheric irregularities. Analysis of Pioneer 10 radio-occultation measurements reveals that the Jovian ionosphere possesses electron-density irregularities which are very similar to those found in the earth's ionosphere. This is the first time such irregularities have been found in a planetary ionosphere other than that of the earth. The Pioneer 10 results indicate that the spatial wave-number spectrum of the electron-density irregularities is close to the Kolmogorov spectrum and that the outer scale size is greater than the Fresnel size (6.15 km). This type of spectrum suggests that the irregularities are probably produced by the turbulent dissipation of irregularities larger than the outer scale size.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 81; July 1
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