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NASA NTRS1981

Mean molecular weight and hydrogen abundance of Titan's atmosphere

The 200-600/cm continuum opacity in the troposphere and lower stratosphere of Titan is inferred from thermal emission spectra from the Voyager 1 IR spectrometer (IRIS). The surface temperature and mean molecular weight are between 94 and 97 K and between 28.3 and 29.2 AMU, respectively. The mole fraction of molecular hydrogen is 0.002 + or - 0.001, which is equivalent to an abundance of approximately 0.2 + or - 0.1 km amagat.

Samuelson, R. E.↗

NASA NTRS1981

Radar investigation of asteroids

Software to support all stages of asteroid radar observation and data analysis is developed. First-order analysis of all data in hand is complete. Estimates of radar cross sections, circular polarization ratios, and limb-to-limb echo spectral bandwidths for asteroids 7 Iris, 16 Psyche, 97 Klotho, 1862 Apollo, and 1915 Quetzalcoatl are reported. Radar observations of two previously unobserved asteroids were conducted. An Aten asteroid, 2100 Ra-Shalom, with the smallest known semimajor axis (0.83) was detected. Preliminary data reduction indicates a circular polarization ratio comparable to those of Apollo, Quetzalcoatl, and Toro.

Ostro, S. J.↗

NASA NTRS1982

A review of acetylene, ethylene and ethane molecular spectroscopy for planetary applications

Spectroscopic work in acetylene, ethylene and ethane, are of particular interest since the Voyager IRIS observations of Jupiter. Acetylene and ethane but not ethylene were observed in the Jovian spectrum. Two fundamental bands of the observed gases are used to determine the spatial distribution of these hydrocarbons on Jupiter and to illuminate the photochemistry of these species. The 100 to 1000 cm region is discussed and selected examples of current laboratory work are given.

Maguire, W. C.↗

NASA NTRS1982

Line intensities from band and diode laser measurements: Neutrino 4 of CH4

The experimental data and theoretical work on the 7.7 micron band of methane are reviewed. This band is particularly relevant in studies of the atmospheres of Jupiter, Saturn and the other outer planets. Methane spectra taken from the infrared spectrometer (IRIS) aboard Voyager, and a temperature profile derived by inverting those data, both for hydrogen and methane are presented.

Fox, K.↗

NASA NTRS1981

Thermal structure and dynamics of the Jovian atmosphere. I - The Great Red Spot

Temperatures and thermal winds over the Great Red Spot (GRS) are derived from Voyager IRIS data for atmospheric pressures between 3 and 500 mbar. A cold tropopause implies a decrease in anticyclonic vorticity with height above 500 mbar through the lower stratosphere. Observations at 5 microns indicate that there is little emission from the GRS itself, although there is enhanced emission from a ring around it. The behavior of the tropopause and 5 micron temperatures are considered to be results of circulation which rises within the GRS and subsides in the area around it. Results are discussed in the context of several theoretical models of the GRS, and latent heat release as an energy source is considered. Dynamical scalings based on an axisymmetric frictionally controlled vortex indicate that the large-scale dynamics of the GRS are linear, as opposed to those of a tropical cyclone which are nonlinear.

Flasar, F. M.↗

NASA NTRS1981

Thermal structure and dynamics of the Jovian atmosphere. II - Visible cloud features

Thermal structures including major white ovals, hot spot regions, barges and a belt zone pair in the Jovian atmosphere are investigated using Voyager IRIS data. Atmosphere above anticyclonic features is cold relative to the immediate surroundings in the upper troposphere and tropopause region, which is consistent with upwelling and divergence in that part of the atmosphere. Localized cyclonic features are warm relative to their surroundings which implies subsidence with accompanying convergence. Thermal wind shear indicates a decay of the vorticity with height in the upper troposphere and lower stratosphere, and vertical velocities imply an upper limit of vertical mixing times near the tropopause of about 20 years. Various possible models are also examined, including radiative heating, vertical wave propagation, and thermally indirect merdional cells.

Conrath, B. J.↗

NASA NTRS1981

The response of ozone to solar activity variations - A review

The effects of solar UV variations on the ozone concentration in the atmosphere are studied with respect to determinations of the global mean ozone concentrations as measured by satellite instrumentation. The Nimbus 4 satellite revealed an NO presence, which catalytically destroys ozone, during a solar proton event. An 11-year UV variability has been detected at increasing wavelengths above 1500 A, an energy band which causes photolysis of O2 into O3, N2O into NO, and NO production in the stratosphere. The latter two reactions decrease ozone destruction. IR interferometer spectrometer (IRIS) data is cited to show an ozone variation of about 3%, which is possible with a 20% solar UV variability at 1800 A; the variability has been confirmed to exist by measurements taken from the Atmospheric Explorer E satellite.

Keating, G. M.↗

NASA NTRS1981

Ocular torsion on earth and in weightlessness

Otolith function is studied by means of measurements of ocular torsion under various acceleration environments on earth and in weightlessness. Photographic measurements of ocular torsion as indicated by the rotation of landmarks on the iris with respect to head-fixed fiducial marks were obtained in subjects undergoing horizontal linear acceleration in a ground-based version of the space sled, lateral acceleration from weightlessness during pullout from the free-fall portion of parabolic flight, and optokinetic stimulation about the roll axis in the supine position in the laboratory and during weightlessness. The responses of ocular torsion to horizontal acceleration are in agreement with a simple low-order linear system with a dominant time constant of 0.33 sec, with a transfer function fit by a model with a pure delay of 0 to 400 msec and a first-order lag. In the pullout experiment, torsion was not observed in response to the onset of acceleration in the right-ear-down position, although it was present in response to the lateral stimulus. Results of the roll vection experiments indicate the independence of ocular torsion and visually induced tilt. In addition, an automatic video system using a soft contact lens target is presented which has been developed for ocular torsion measurements.

Young, L. R.↗

NASA NTRS1981

Planetary-scale wave structure in the Martian atmosphere

Wave-like perturbations are found in the Mariner 9 IRIS atmospheric temperature data during late Northern Hemisphere winter in a latitude band between 45 deg N and 65 deg N. The nature of the data base prevents a unique separation of spatial and temporal behavior, but Fourier analysis of the data constrains the waves to discrete combinations of planetary wavenumber and period. One major spectral component possesses a meridional amplitude cross section with a maximum near the 1 mbar level at 60 deg N and is strongly correlated with the circumpolar jet observed in thermal winds calculated from the mean meridional temperature cross section. This feature is consistent with the low-wavenumber baroclinic waves observed in Viking Lander data, and the vertical structure reflects the behavior anticipated for a vertically penetrating quasi-geostrophic disturbance. Other possible origins for the wave cannot be ruled out, however. Among these is a stationary wave forced by wavenumber-2 topographic relief.

Conrath, B. J.↗

NASA NTRS1982

Properties of dust in the Martian atmosphere and its effect on temperature structure

Data from the Viking lander imaging experiment and the IRIS experiment on board the Mariner 9 Orbiter are used to develop a one-dimensional radiative-convective model to describe the Mars temperature profile. Photography was employed to determine the optical depth, mean size, shape, visible absorption coefficient, and vertical distribution of aerosols in the Mars atmosphere. The calculation procedures are outlined, particularly for the particle size distribution function, which indicated a cross-sectional average particle radius of 2.5 microns. Dust-free conditions in the atmosphere near the equator and at lower altitudes permit full surface absorption of sunlight and subsequent adiabatic lapse rates. Difficulties were encountered in accurately modeling temperature profiles to fit Viking lander data, and resultant variations are attributed to effects of both suspended dust particles and large scale circulation.

Pollack, J. B.↗

NASA NTRS1982

The C/H ratio in Jupiter from the Voyager infrared investigation

From a selection Voyager IRIS spectra corresponding to cloud-free areas of Jupiter, the CH4/H2 volume ratio in the atmosphere of this planet has been determined to be equal to 0.00195 + or - 0.00022, which corresponds to 2.07 + or - 0.24 times the solar value of Lambert (C/H = 0.00047). The estimate of errors includes both instrument noise and systematic uncertainties. Implications of this result for the formation and evolution of Jupiter are discussed.

Gautier, D.↗

NASA NTRS1981

Improved accuracy of the remote sensing of sea surface temperature

A method is described for determining the water vapor content to within + or - 0.4 g/sq cm from remotely sensed radiances in three infrared channels, 11, 13, 18 microns. Using this method, it is possible to significantly improve the accuracy of sea surface temperature (SST) over what is obtainable with the two channel technique. A radiative computational scheme for the radiative transfer equation is used to study the manner in which the equivalent radiative temperature of the atmosphere changes as a function of wave number for different atmospheric conditions. Average climatological conditions are used to simulate the radiative response of the atmosphere. This radiative transfer simulation is used to compute brightness temperatures for radiosonde profiles obtained from oceanographic ships, which temperatures are in turn used to estimate the SST. Nimbus 4 IRIS spectral measurements corresponding to the profiles were used in the same way for purposes of comparison.

Dalu, G.↗

NASA NTRS1983

The C-12/C-13 ratio in Jupiter from the Voyager infrared investigation

An analysis of the v(4) band of CH4 in the spectra recorded by the Voyager 1 IRIS experiment has yielded a C-12/C-13 ratio in Jupiter that is 160 plus 40 or minus 55, or 1.8 plus 0.4 or minus 0.6 times the terrestrial value. It is noted that while no plausible theory predicts such a difference between the C-12/C-13 ratio values of Jupiter and the inner solar system, values of this ratio in the solar neighborhood 4.5 million years ago, inferred from recent interstellar medium measurements, are compatible with the present determination in Jupiter. The Jovian, rather than the terrestrial value, would then be representative of the carbon isotope ratio in the primitive solar nebula.

Courtin, R.↗

NASA NTRS1983

Design considerations for a real-time ocular counterroll instrument

A real-time algorithm for measuring three-dimensional movement of the human eye, especially torsional movement, is presented. As its input, the system uses images of the eyeball taken at video rate. The amount of horizontal and vertical movement is extracted using a pupil tracking technique. The torsional movement is then measured by computing the discrete cross-correlation function between the circular samples of successive images of the iris patterns and searching for the position of the peak of the function. A local least square interpolation around the peak of the cross-correlation function is used to produce nearly unbiased estimates of torsion angle with accuracy of about 3-4 arcmin. Accuracies of better than 0.03 deg are achievable in torsional measurement with SNR higher than 36 dB. Horizontal and vertical rotations of up to + or - 13 deg can occur simultaneously with torsion without introducing any appreciable error in the counterrolling measurement process.

Hatamian, M.↗

NASA NTRS1983

Amalthea - Implications of the temperature observed by Voyager

The temperature profile of Amalthea's surface layer is modeled as a function of location and time of day, assuming a triaxial ellipsoid shape and thermal properties similar to those of the lunar soil. Although the major heat source is direct insolation, temperatures are slightly increased by thermal radiation from Jupiter, sunlight reflected from the planet, and charged particle bombardment. Possible sources of error in the model are discussed in detail, including satellite shape effects, unusually low emissivity, uncommonly rough surface, abnormal thermal inertia, charged particle flux variability, and Joule heating. Voyager 1 IRIS observations suggest that the Amalthean surface has an emissivity near unity, but cannot put any useful limits on the thermal inertia of the Amalthean surface layer.

Simonelli, D. P.↗

NASA NTRS1983

A two-stage mechanism for escape of Na and K from Io

A two-stage process is presented to identify Io as the source of Na and K ions in the Io plasma torus. The Voyager I IRIS experiment recorded an SO2 abundance of 0.2 cm atm in the Io subsolar region, and further calculations determined that the S(+) and O(+) would have sufficient energy to penetrate the Io atmosphere and produce sputtering of surface atoms at a rate of 800 million/sq cm per sec. If K, Na, and S are present on the surface in cosmic proportions, then an evenly applied sputter distribution would produce the same abundances of sputtered Na and K as observed in the Na and K clouds around Io. Sputtered into the atmosphere, the ions undergo thermal Jean's escape and attain velocities of at least 2.6 km/sec. The sputtering ions are a factor of two greater on the Jupiter side than on the solar side, in agreement with asymmetries measured by the Voyager.

Summers, M. E.↗

NASA NTRS1983

A laboratory study of the 8.65 micron fundamental of (C-12)H3D at temperatures relevant to Titan's atmosphere

Spectral transmittance measurements have been performed in the nu6-fundamental of (C-12)H3D at 153 K. Relevant to the studies of the emission spectra of Titan recorded by the IRIS instruments on board Voyagers 1 and 2, N2 has been used as the broadening gas. Excellent agreement between experimental and theoretical spectral transmittance has been the result of using N2-broadened line widths and their dependence upon temperature measured in the nu2-fundamental and S = 63.6 per(sq cm atm) for the absolute intensity of the nu6-fundamental.

Varanasi, P.↗

NASA NTRS1984

Wavenumber dependent investigation of the terrestrial infrared radiation budget with two versions of the LOWTRAN5 band model

Two versions of the LOWTRAN5 radiance code are used in a study of the earth's clear sky infrared radiation budget in the interval 30 per cm (333.3 microns) to 3530 per cm (2.8 microns). One version uses 5 per cm resolution and temperature dependent molecular absorption coefficients, and the second uses 20 per cm resolution and temperature independent molecular absorption coefficients. Both versions compare well with Nimbus 3 IRIS spectra, with some discrepancies at particular wavenumber intervals. Up and downgoing fluxes, calculated as functions of latitude, are displayed for wavenumbers at which the principle absorbers are active. Most of the variation of the fluxes with latitude is found in the higher wavenumber intervals for both clear and cloudy skies. The main features of the wavenumber integrated cooling rates are explained with reference to calculations in more restricted wavenumber intervals. A tropical lower tropospheric cooling maximum is produced by water vapor continuum effects in the 760-1240 per cm window. A secondary upper tropospheric cooling maximum, with wide meridional extent, is produced by water vapor rotational lines between 30-430 per cm. Water vapor lines throughout the terrestrial infrared spectrum prevent the upflux maximum from coinciding with the surface temperature maximum.

Charlock, T. P.↗