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M. G. Tomasko R. Boese A. P. Ingersoll A. A. Lacis S. S. Limaye J. B. Pollack A. Seiff A. I. Stewart V. E. Suomi F. W. Taylor 《Space Science Reviews》1977,20(4):389-412
Current knowledge of the temperature structure of the atmosphere of Venus is briefly summarized. The principal features to be explained are the high surface temperature, the small horizontal temperature contrasts near the cloud tops in the presence of strong apparent motions, and the low value of the exospheric temperature. In order to understand the role of radiative and dynamical processes in maintaining the thermal balance of the atmosphere, a great deal of additional data on the global temperature structure, solar and thermal radiation fields, structure and optical properties of the clouds, and circulation of the atmosphere are needed. The ability of the Pioneer Venus Orbiter and Multiprobe Missions to provide these data is indicated. 相似文献
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Tomasko M.G. Buchhauser D. Bushroe M. Dafoe L.E. Doose L.R. Eibl A. Fellows C. Farlane E. M Prout G.M. Pringle M.J. Rizk B. See C. Smith P.H. Tsetsenekos K. 《Space Science Reviews》2002,104(1-4):469-551
The payload of the Huygens Probe into the atmosphere of Titan includes the Descent Imager/Spectral Radiometer (DISR). This
instrument includes an integrated package of several optical instruments built around a silicon charge coupled device (CCD)
detector, a pair of linear InGaAs array detectors, and several individual silicon detectors. Fiber optics are used extensively
to feed these detectors with light collected from three frame imagers, an upward and downward-looking visible spectrometer,
an upward and downward looking near-infrared spectrometer, upward and downward looking violet phtotometers, a four-channel
solar aerole camera, and a sun sensor that determines the azimuth and zenith angle of the sun and measures the flux in the
direct solar beam at 940 nm. An onboard optical calibration system uses a small lamp and fiber optics to track the relative
sensitivity of the different optical instruments relative to each other during the seven year cruise to Titan. A 20 watt lamp
and collimator are used to provide spectrally continuous illumination of the surface during the last 100 m of the descent
for measurements of the reflection spectrum of the surface. The instrument contains software and hardware data compressors
to permit measurements of upward and downward direct and diffuse solar flux between 350 and 1700 nm in some 330 spectral bands
at approximately 2 km vertical resolution from an alititude of 160 km to the surface. The solar aureole camera measures the
brightness of a 6° wide strip of the sky from 25 to 75° zenith angle near and opposite the azimuth of the sun in two passbands
near 500 and 935 nm using vertical and horizontal polarizers in each spectral channel at a similar vertical resolution. The
downward-looking spectrometers provide the reflection spectrum of the surface at a total of some 600 locations between 850
and 1700 nm and at more than 3000 locations between 480 and 960 nm. Some 500 individual images of the surface are expected
which can be assembled into about a dozen panoramic mosaics covering nadir angles from 6° to 96° at all azimuths. The spatial
resolution of the images varies from 300 m at 160 km altitude to some 20 cm in the last frames. The scientific objectives
of the experiment fall into four areas including (1) measurement of the solar heating profile for studies of the thermal balance
of Titan; (2) imaging and spectral reflection measurements of the surface for studies of the composition, topography, and
physical processes which form the surface as well as for direct measurements of the wind profile during the descent; (3) measurements
of the brightness and degree of linear polarization of scattered sunlight including the solar aureole together with measurements
of the extinction optical depth of the aerosols as a function of wavelength and altitude to study the size, shape, vertical
distribution, optical properties, sources and sinks of aerosols in Titan's atmosphere; and (4) measurements of the spectrum
of downward solar flux to study the composition of the atmosphere, especially the mixing ratio profile of methane throughout
the descent. We briefly outline the methods by which the flight instrument was calibrated for absolute response, relative
spectral response, and field of view over a very wide temperature range. We also give several examples of data collected in
the Earth's atmosphere using a spare instrument including images obtained from a helicopter flight program, reflection spectra
of various types of terrain, solar aureole measurements including the determination of aerosol size, and measurements of the
downward flux of violet, visible, and near infrared sunlight. The extinction optical depths measured as a function of wavelength
are compared to models of the Earth's atmosphere and are divided into contributions from molecular scattering, aerosol extinction,
and molecular absorption. The test observations during simulated descents with mountain and rooftop venues in the Earth's
atmosphere are very important for driving out problems in the calibration and interpretion of the observations to permit rapid
analysis of the observations after Titan entry.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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R. G. Knollenberg J. Hansen B. Ragent J. Martonchik M. Tomasko 《Space Science Reviews》1977,20(3):329-354
The current state of knowledge of the Venusian clouds is reviewed. The visible clouds of Venus are shown to be quite similar to low level terrestrial hazes of strong anthropogenic influence. Possible nucleation and particle growth mechanisms are presented. The Pioneer Venus experiments that emphasize cloud measurements are described and their expected findings are discussed in detail. The results of these experiments should define the cloud particle composition, microphysics, thermal and radiative heat budget, rough dynamical features and horizontal and vertical variations in these and other parameters. This information should be sufficient to initialize cloud models which can be used to explain the cloud formation, decay, and particle life cycle. 相似文献
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M.G. Tomasko L.R. Doose P.H. Smith 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(9):71-79
The Solar Flux Radiometer (LSFR) experiment on the large probe of the Pioneer Venus (PV) mission made detailed measurements of the vertical profile of the upward and downward broadband flux of sunlight at a solar zenith angle of 65.7°. These data have been combined with cloud particle size distribution measurements on the PV mission to produce a forward-scattering model of the Venus clouds. The distribution of clouds at high altitudes is constrained by measurements from the PV orbiter. Below the clouds the visible spectrum and flux levels are consistent with Venera measurements at other solar zenith angles. The variations in the optical parameters with height and with wavelength are summarized in several figures. The model is used to evaluate the solar heating rate at cloud levels as a function of altitude, solar longitude, and latitude for use in dynamical studies. 相似文献
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