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NASA NTRS1976

Mariner 9 ultraviolet spectrometer experiment - Bright-limb observations of the lower atmosphere of Mars

Analysis of the bright-limb profiles obtained by the Mariner 9 ultraviolet spectrometer during the December 1971 dust storm on Mars shows that the dust extended to an altitude of plus or minus 10 km, with a sharp cutoff in altitude distribution. Above the dust layer, the reflected signal is characterized by Rayleigh scattering in the wavelength interval 2100 to 3500 A. Detached haze layers were detected at an altitude of 70 plus or minus 10 km at the top of the dust layer. The haze layers have a nominal optical thickness of about 0.0001 and a geometrical thickness of 3 to 10 km and are probably a condensate of small CO2 or H2O ice particles (mean radius less than 0.1 micron). Similar features were revealed in Mariner 9 TV pictures of the limb.

Ajello, J. M.↗

NASA NTRS1976

The aerosol distribution in Uranus' atmosphere - Interpretation of the hydrogen spectrum

New observations of Uranus' combined H2 spectrum have been obtained. An analysis, emphasizing the leverage provided by the S3(0) quadrupole line, leads to strong constraints on Uranus' bulk aerosol distribution with depth. Using an inhomogeneous model atmosphere program which includes Rayleigh scattering for gases and a 1 plus cos theta phase function for cloud layers, it is shown that Uranus' H2 spectrum implies a cloud layer (or dense aerosol) at a depth from 500 to 700 km-amagat H2. It also implies negligible aerosol scattering in the 280 to 450 km-amagat H2 region and a thin haze at 100 to 200 km-amagat H2 depths. The low albedo in very strong CH4 bands indicates that there is negligible aerosol scattering in Uranus' radiative zone. Hydrogen appears to be more abundant than the sum of all other atmospheric gases. The C/H ratio deep in Uranus' atmosphere is strongly enhanced over the solar value. Accurate limb-darkening measurements in and near strong CH4 bands would be effective in specifying Uranus' aerosol distribution in greater detail.

Trafton, L.↗

NASA NTRS1977

Aerosol physical properties in the stratosphere (APPS) radiometer design

The measurement concepts and radiometer design developed to obtain earth-limb spectral radiance measurements for the Aerosol Physical Properties in the Stratosphere (APPS) measurement program are presented. The measurements made by a radiometer of this design can be inverted to yield vertical profiles of Rayleigh scatterers, ozone, nitrogen dioxide, aerosol extinction, and aerosol physical properties, including a Junge size-distribution parameter, and a real and imaginary index of refraction. The radiometer design provides the capacity for remote sensing of stratospheric constituents from space on platforms such as the space shuttle and satellites, and therefore provides for global measurements on a daily basis.

Gray, C. R.↗

NASA NTRS1977

Seismotectonic, structural, volcanologic, and geomorphic study of New Zealand; indigenous forest assessment in New Zealand; mapping, land use, and environmental studies in New Zealand, volume 1

The author has identified the following significant results. Results of the atmospheric extinction measurements show clearly the greater opacity of the atmosphere in MSS band 4 which is due to Rayleigh scattering. Atmospheric water vapor absorbs strongly in a wide region between 900 nm and 1000 nm, and this results in a consistently higher extinction coefficient than would otherwise be expected in MSS band 7. The short term fluctuations tend to be greater in band 7 than in the other bands, and this effect is probably due to variations of water vapor concentration in the instrument line of sight. These high extinction coefficients and short term fluctuations in band 7 were observed at Menindee which is in a semi-desert region in western New South Wales.

Probine, M. C.↗

NASA NTRS1976

The far ultraviolet /1200-1900 A/ spectrum of Jupiter obtained with a rocket-borne multichannel spectrometer

Far-ultraviolet spectra of Jupiter with a significant improvement in sensitivity and spectral resolution have been obtained from a sounding rocket by using a 10-channel spectrometer behind a pointing telescope. The major results obtained from these spectra are: (1) measurement of the Jovian H I 1216-A brightness (a comparison with other measurements indicates that the Ly-alpha emission is likely to be variable); (2) measurement of the wavelength-dependent albedo for Rayleigh-scattered solar radiation from about 1550 to 1875 A with approximately 25-A resolution, making it possible to set revised upper limits on the abundances of some of the minor constituents in the upper Jovian atmosphere; and (3) a demonstration that weak emissions between approximately 1250 and 1500 A and near 1600 A are probably the Lyman bands of H2 excited by low-energy electrons.

Giles, J. W.↗

NASA NTRS1977

Planetary isophotes as a clue to aerosol characteristics

A study was made to see how much information could be extracted from the Mariner 9 Mars isophotes taken at phase angle roughly 60 deg. Minnaert functions and both isotropic and Rayleigh scattering could easily be ruled out, and it was essential to use forward-peaked phase functions computed from Mie theory. Isophotes similar to those observed are plotted assuming a semi-infinite dust cloud with a considerable variation in particle properties and size distribution, so long as the ratio of the multiply to singly scattered light is held within certain limits. These conditions are met by micron-sized, moderately absorbing mineral grains whose mean size should not be much larger than a micron. It was also found that a dust cloud of finite optical thickness bounded from below by a Lambert ground would fit the isophote data.

Kattawar, G. W.↗

NASA NTRS1977

Atmospheric transformation of solar radiation reflected from the ocean

Airborne measurements of the brightness spectrum of the Atlantic Ocean in the wavelength region from 0.4 to 0.7 micron are analyzed. These measurements were made over a tropical region of the Atlantic from an aircraft at heights of 0.3 and 10.5 km during the TROPEX-72 experiment. The results are used to estimate the contribution of the atmosphere to the overall brightness of the ocean-atmosphere system. It is concluded that: (1) the atmosphere decreases the absolute brightness of the ocean by a factor of 5 to 10 and also strongly affects the spectral behavior of solar radiation reflected from the ocean surface; (2) the atmospheric contribution to overall brightness may vary considerably under real conditions; (3) finely dispersed particles and Rayleigh scattering affect the spectral distribution of solar radiation; and (4) the spectral composition of ocean-atmosphere brightness may be completely governed by the atmosphere.

Malkevich, M. S.↗

NASA NTRS1977

Absolute calibration in the 1750 - 3350 A region

The absolute flux measurements in the rocket ultraviolet made by Bohlin, Frimout, and Lillie (BFL) are revised using a more correct treatment of the air extinction that enters the air calibration of their instrument. The absorption by molecular oxygen and ozone, Rayleigh scattering, and extinction by aerosols is tabulated for general use in ultraviolet calibrations performed in air. The revised absolute flux of eta UMa and final fluxes for alpha Lyr and zeta Oph are presented in the 1750-3350 A region. The absolute flux of the star eta UMa is compared to four other independent determinations in the 1200-3400 A region and a maximum difference of 35% is found near 1500 A between the OAO-2 and Apollo 17 fluxes. The rocket measurements of BFL, the ANS and TD-1 satellite data, and the Apollo 17 data are compared to the ultraviolet fluxes from the OAO-2, demonstrating a photometric reproducibility of about + or - 3 percent. Therefore, all four sets of spectrophotometry can be reduced to a common absolute scale.

Strongylis, G. J.↗

NASA NTRS1978

Optical measurement methods in thermogasdynamics

A review is presented of a number of optical methods of flow measurements. Consideration is given to such spectroscopic methods as emission and absorption techniques, electron beam-stimulated fluorescence, and light scattering - Rayleigh, Raman and Mie - methods. The following visualization methods are also discussed: shadow photography, schlieren photography, interferometry, holographic interferometry, laser anemometry, particle holography, and electron-excitation imaging. A large bibliography is presented and the work is copiously illustrated with figures and photographs.

Stursberg, K.↗

NASA NTRS1977

Occultation of Epsilon Geminorum by Mars. II - The structure and extinction of the Martian upper atmosphere

The occultation of Epsilon Geminorum by Mars on April 8, 1976, was observed at three wavelengths and 4-ms time resolution with the 91-cm telescope aboard NASA's G. P. Kuiper Airborne Observatory. Temperature, pressure, and number-density profiles of the Martian atmosphere were obtained for both the immersion and emersion events. Within the altitude range 50-80 km above the mean surface, the mean temperature is about 145 K, and the profiles exhibit wavelike structures with a peak-to-peak amplitude of 35 K and a vertical scale of about 20 km. The ratio of the refractivity of the atmosphere at 4500 A and 7500 A is consistent with the atmospheric composition measured by Viking 1. From the 'central flash' - a bright feature in the light curve midway between immersion and emersion - an optical depth at 4500 A of 3.3 + or - 1.7 per km atm (about 0.23 per equivalent Martian air mass) is found for the atmosphere about 25 km above the mean surface near the south polar region. This large value and its weak wavelength dependence rule out Rayleigh scattering as the principal cause of the observed extinction.

Elliot, J. L.↗

NASA NTRS1978

Detectability limit and uncertainty considerations for laser induced fluorescence spectroscopy in flames

Laser induced fluorescence spectroscopy of flames is discussed, and derived uncertainty relations are used to calculate detectability limits due to statistical errors. Interferences due to Rayleigh scattering from molecules as well as Mie scattering and incandescence from particles have been examined for their effect on detectability limits. Fluorescence trapping is studied, and some methods for reducing the effect are considered. Fluorescence trapping places an upper limit on the number density of the fluorescing species that can be measured without signal loss.

Daily, J. W.↗

NASA NTRS1977

The correction of Landsat data for the effects of haze, sun angle, and background reflectance

A technique has been developed for simulating the effects of haze, sun angle, and background reflectance in Landsat data and correcting for them. The atmospheric model assumes a two-layer atmosphere: a Rayleigh scattering molecular layer and a Mie scattering haze layer next to the earth's surface. Reflection and transmission matrices describe the reflection and transmission properties of the plane parallel scattering layers. The multispectral scanner response is computed for various values of the parameters under evaluation. This yields expressions for Landsat gray-scale levels used for determining the effect of changes in any parameter. The Atmospheric Correction computer program is used to determine the haze level from the data, to compute the reflectance, and to interpolate in order to find the correction coefficients necessary to make the desired correction.

Potter, J. F.↗

NASA NTRS1977

Occultation studies of planets and satellites: The occultation of epsilon Geminorum by Mars

The occultation of epsilon Geminorum by Mars on 1976 April 8 was observed at three wavelengths and 4 ms time resolution with the 91 cm telescope. Temperature, pressure, and number density profiles of the Martian atmosphere were obtained for both the immersion and emersion events. Within the altitude range of 50 to 80 km above the mean surface, the mean temperature is 145 K, and the profiles exhibit wavelike structures with a peak to peak amplitude of 35 K and a vertical scale of about 20 km. The ratio of the refractivity of the atmosphere at 4500 A and 7500 A, determined from the time shift of the light curves for these wavelengths, is consistent with the atmospheric composition measured by Viking 1, 15 weeks later. From the central flash - a bright feature in the light curve midway between immersion and emersion - an optical depth is found at 4500 A of 3.3 plus or minus 1.7 per km atm (about 0.23 per equivalent Martian air mass) for the atmosphere about 25 km above the mean surface, near the south polar region. This large value and its weak wavelength dependence rule out Rayleigh scattering as the principal cause of the observed extinction.

Elliot, J. L.↗

NASA NTRS1977

Feature discrimination and detection probability in synthetic aperture radar imaging system

Images obtained using synthetic aperture radar (SAR) systems can only represent the intensities of resolution cells in the scene of interest probabilistically since radar receiver noise and Rayleigh scattering of the transmitted radiation are always present. Consequently, when features to be identified differ only by their contribution to the mean power of the radar return, discrimination can be treated by detection theory. In this paper, we develop a 'sufficient statistic' for discriminating between competing features and compare it with some suboptimal methods frequently used. Discrimination is measured by probability of detection error and depends on number of samples or 'looks', signal-to-noise ratio (SNR), and ratio of mean power returns from the competing features. Our results show discrimination and image quality rapidly saturate with SNR (very small improvement for SNR not less than 10 dB) but continue to improve with increasing number of looks.

Lipes, R. G.↗

NASA NTRS1979

High resolution atmospheric transmission calculations down to 28.7 km in the 200-243-nm spectral range

Decrease in stratospheric ozone absorption and increase in oxygen absorption with decreasing wavelength combine to produce a window of maximum atmospheric transmission near 210 nm. Since solar radiation in this spectral region dissociates molecular oxygen, the deep atmospheric penetration at this wavelength is of particular aeronomical interest. High resolution calculations of the transmittance down to 28.65 km were made for the 200-243-nm spectral range in this window region, in support of a stratospheric balloon flight from Fort Churchill in July 1974. The calculations were made by dividing the atmosphere into layers which were chosen so that each could be assumed homogeneous; optical depths were calculated separately for each of these layers and then summed to obtain the over-all transmittance of the atmosphere. Absorption by molecular oxygen (line and continuum) and by ozone was included, as well as extinction through Rayleigh scattering by air molecules. The calculated transmittances were combined with high altitude (above 100-km) rocket measurements of the sun-center spectrum and center-to-limb variations to give residual high resolution solar spectral flux for several altitudes and solar zenith angles.

Cann, M. W. P.↗

NASA NTRS1979

Absolute calibration in the 1750 A-3350 A region

The absolute flux measurements in the rocket ultraviolet made by Bohlin, Frimout, and Lillie (BFL) are revised using a more correct treatment of the air extinction that enters the air calibration of their instrument. The absorption by molecular oxygen and ozone, Rayleigh scattering, and extinction by aerosols is tabulated for general use in ultraviolet calibrations performed in air. The revised absolute flux of Eta UMa and final fluxes for Alpha Lyr and Zeta Oph are presented in the 1750 A-3350 A region. The absolute flux of the star Eta UMa (B3 V) is compared to four other independent determinations in the 1200 A-3400 A region and a maximum difference of 35% is found near 1500 A between the OAO-2 and Apollo 17 fluxes. Longward of 1700 A the typical scatter in the different determinations is only plus or minus 5%. The rocket measurements of BFL, the ANS and TD-1 satellite data, and the Apollo 17 data are compared to the ultraviolet fluxes from the OAO-2, demonstrating a photometric reproducibility of about plus or minus 3%. Therefore, all four sets of spectrophotometry can be reduced to a common absolute scale.

Strongylis, G. J.↗

NASA NTRS1978

On the detectability of a metallized lunar core

Calculations are made of the expected complex electromagnetic gain of the moon using current models of the internal bulk electrical conductivity with the addition of conducting cores of varying radii. The results show that the phase of the response (gain) function is sensitive to the radius and conductivity. The gain amplitude varies in a complicated way for frequencies above (0) 10 microHz. Below this 'corner' frequency, the square of the gain amplitude varies approximately quadratically with frequency and therefore inverse quadratically with hydromagnetic wavelength in the solar wind. The addition of conducting cores alters this dependence. A 'flat' frequency independent range for the gain amplitude evolves, which is a second way, in principle, to detect a conducting core. The departure from the lambda to the -4th Rayleigh scattering law is due to a combination of the conductivity of the moon and the relative unimportance of confinement of the induced fields at the very low frequencies of interest for core detection. For some core parameters, detection is not feasible with current data, and data recording times varying from several months to centuries would be required.

Wiskerchen, M. J.↗

NASA NTRS1979

The diameter and reflectance of Triton

The surface reflectance, radius and geometric albedo of Triton are investigated. Image tube spectra of the reflectance of the satellite between 3200 and 7400 A are presented which indicate that the surface is composed mainly of rocky (non-icy) material, with violet absorption suggesting a composition similar to that of lunar fines, terrestrial igneous rocks and chondrites. Photometric/radiometric calculations based on measurements of the 20-micron thermal flux and the known visual magnitude of Triton reveal an upper limit of 5280 km to its diameter, and a lower limit of 0.19 to its geometric albedo. Computations of Rayleigh scattering in a potential inert atmospheric component are also presented which appear to preclude the presence of large quantities of nitrogen and noble gases on Triton.

Cruikshank, D. P.↗