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At least 1,135 records · Page 63
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NASA NTRS1985

Geophysical Interpretation of Venus Gravity Data

The subsurface distribution of Venus was investigated through the analysis of the data from Pioneer Venus Orbiter (PVO). In particular, the Doppler tracking data were used to map the gravitational potential. These were compared to the topographic data from the PVO radar (ORAD). In order to obtain an unbiased comparison, the topography data obtained from the PVO-ORAD were filtered to introduce distortions which are the same as those of the gravity models. Both the gravity and filtered topography maps are derived by two stage processes with a common second stage. In the first stage, the topography was used to calculate a corresponding spacecraft acceleration under the assumptions that the topography has a uniform given density and no compensation. In the second stage, the acceleration measures found in the first stage were passed through a linear inverter to yield maps of gravity and topography. Because these maps are the result of the same inversion process, they contain the same distortion; a comparison between them is unbiased to first order.

Reasenberg, R. D.↗
NASA NTRS1985

Martian Fretted Terrain Morphometry Interpreted Using Principal Components Analysis

Martian fretted terrain is an extensive area of complex topography characterized by smooth, flat-floor valleys and mesas separated by abrupt escarpments along the boundary of heavily cratered uplands. The Deuteronilus-Protonilus region of the fretted terrain between latitude 35 degrees N and 50 degrees N and between 305 degrees W and 350 degrees W longitude was selected for quantitative landform study with the use of principal components analysis (PCA). The morphometry of upland mesa remnants and debris aprons was digitized with respect to latitude, longitude, and distance from the cratered terrain boundary (CTB). The PCA demonstrates that there are definable spatial variations in morphology with respect to longitude and latitude which suggest that the degradation along the CTB proceeded toward the southwest. The PCA also showed that there are organized relationships within the fretted landforms irrespective of their location. Finally, PCA indicated that an orientation of the degraded mesas exists which may be controlled by structure.

Kochell, R. C.↗
NASA NTRS1985

Geologic Interpretation of Remote Sensing Data for the Martian Volcano, Ascraeus Mons

Results of an investigation to relate remotely determined physical properties on Ascraeus Mons to the geologic history of the volcano are summarized. Products include a 1:2,000,000-scale photogeologic map of Ascraeus Mons and its environs; a 1:250,000-scale corrected thermal-inertia map of the summit caldera complex; four corrected thermal-inertia profiles across the volcano from high-resolution thermal data; fourteen low-resolution thermal sequences providing corrected thermal inertias for the volcano throughout half a Martian year; and a calibrated three-color photograph of the volcano. These data were combined with published spectral-reflectance, radar, and atmospheric water-vapor data relating to Acraeus Mons. Photogeologic mapping indicates that the sequence of events at Acraeus Mons is more complex than previously described. The plains surrounding the volcano include numerous flows, some of which can be traced to the flank of the volcano and some to different locations along the Tharsis Ridge. Surface morphology in the summit area is very distinct for features 100 m in scale, but the surface relief and tonal contrast steadily decrease toward the base of the shield, indicating modification by deposition or erosion.

Zimbelman, J.↗
NASA NTRS1984

Analysis and Interpretation of Synthetic Time Strings of Oscillation Data

Artificial strings of solar oscillation data with gaps and noise, corresponding to the output of different spatial filter functions, were analyzed. Peaks in the power spectrum are identified for values of the degree l from 0 to 18, and rotational splitting is estimated. The filters prove effective in facilitating identification of essentially all the real peaks in the power spectrum. Estimates of peak frequencies and amplitudes and rotational splitting frequencies are in reasonably good agreement with the input values. Spurious peaks in autocorrelation spectra correspond to the frequency spacing between power peaks with the same order n, differing by one or two in the degree l.

Mihalas, B. W.↗
NASA NTRS1985

Geophysical interpretation of Venus gravity data

The investigation of the subsurface mass distribution of Venus through the analysis of the data from Pioneer Venus Orbiter (PVO) is presented. The Doppler tracking data was used to map the gravitational potential, which was compared to the topographic data from the PVO radar (ORAD). In order to obtain an unbiased comparison, the topography obtained from the PVO-ORAD was filtered to introduce distortions which are the same as those of our gravity models. The last major software package that was required in order to determine the spectral admittance Z (lambda) was used. This package solves the forward problem: given the topography and its density, and assuming no compensation, find the resulting spacecraft acceleration along a given nominal trajectory. The filtered topography is obtained by processing these accelerations in the same way (i.e., with the same geophysical inverter) as the Doppler-rate data that we use to estimate the gravity maps.

Reasenberg, R. D.↗
NASA NTRS1984

Interpretation of radar returns from the mesosphere, part 2.3A

The study of VHF radar signals from the mesosphere has shown that neutral atmosphere turbulence plays a central role in generating the refractive index irregularities that backscatter the radio waves. It follows that an increase in the turbulent energy dissipation rate will result in a decrease in signal correlation time and an increase in scattered signal power. Thus, in turbulence-generated radar echoes a negative correlation between echo power and signal correlation time (P/C) is expected. P/C also changes as a function of altitude, i.e., it is negative in the upper mesosphere but largely positive in the lower, with the latter thought to be a manifestation of partial reflection from stratified layers of refractive index gradient. Partial reflection would also explain the vertical aspect sensitivity of the scattered signal in the lower mesosphere.

Royrvik, O.↗
NASA NTRS1985

Interpretation of photometric measurements of airless bodies

The scattering properties of the surfaces of airless bodies were observed. These properties are controlled primarily by the following physical parameters: the single scattering albedo, the single particle phase function, the porosity of the upper regolith, and large scale roughness. Comparison of the observations with scattering models reveals both similarities and differences among the airless bodies in the solar system. The textural characteristics of the regolithms of icy satellites appear to be generally similar to those of the Moon and Mercury; differences in the scattering functions are attributed to albedo alone. A notable exception is Europa, which has a much more compact regolith. Io has an especially porous regolith, with void space of about 90%. Although the solar phase curves of the Moon and Mercury are similar, Mercury's phase curve drops off less rapidly at solar phase angles greater than 100 degrees. It is suggested that the Moon is rougher at scales larger than a few mm.

Buratti, B. J.↗
NASA NTRS1985

Experimental test for interpreting the increase in sensibility of doped CR-39

In recent years the sensibility of CR-39 to nuclear tracks has been increased by doping the corresponding monomer with dioctyl phtalate. At this regard, two theoretical approaches are current managed to explain this phenomenon: either the doping react with the active radicals in the chain blocking them, stopping crosslinking between chains, or alternatively that the doping gets between them giving wider space between the crosslinkined chains.

Laville, A.↗
NASA NTRS1985

Interpretation of cosmic-ray anisotropy below 10(14) eV

It is found that the measured data on the degree of anisotropy of cosmic rays are consistent with our proposed nonuniform galactic disk model. Moreover, it is pointed out that the abrupt increase of the anisotropy of cosmic rays beyond 10 to the 14th power eV should imply a change of their mass composition.

Tan, L. C.↗
NASA NTRS1984

Diurnal variations of atmospheric nitric oxide - Ground-based infrared spectroscopic measurements and their interpretation with time-dependent photochemical model calculations

Total vertical column amounts of NO have been derived from infrared solar absorption spectra recorded near sunrise and sunset with the 0.01 per cm resolution Fourier transform interferometer at the national Solar Observatory on Kitt peak (elevation 2095 m, latitude 31.9 degrees N) on February 23, 1981. The results show an increase in NO concentration in the morning, late afternoon values about 40 percent higher than in the morning, and a decrease in NO concentration prior to sunset. The measured diurnal changes in the total vertical column amount are compared with values obtained from time-dependent photochemical calculations.

Rinsland, C. P.↗
NASA NTRS1984

A new interpretation of the Venera 11 spectra of Venus. I - The 0.94 micron water band

Detailed band models for CO2 and H2O absorption are used to reinterpret Venera 11 spectra of the transmitted sunlight at several levels in the Venus atmosphere. An effective path approximation is used to allow for scattering in the clouds. The atmospheric model has 10 layers and uses 211 CO2 and 15 H2O vibrational transitions at 5/cm resolution. The conclusion of Moroz et al. (1979) that the 0.94 micron feature of the spectra indicates a sharp maximum in the water-vapor profile near 50 km is confirmed. It is also confirmed that such a profile fails to account for the spectra in the 1.13 micron water bands.

Young, L. D. G.↗
NASA NTRS1984

Interpretation of He-3 abundance variations in the solar wind

The ion composition instrument (ICI) on ISEE-3 observed the isotopes of helium of mass 3 and 4 in the solar wind almost continuously between August 1978 and July 1982. This period included the increase towards the maximum of solar activity cycle 21, the maximum period, and the beginning of the descent towards solar minimum. Observations were made when the solar wind speed was between 300 and 620 km/s. For part of the period evidence for regular interplanetary magnetic sector structure was clear and a number of He-3 flares occurred during this time.

Coplan, M. A.↗
NASA NTRS1984

Interpretation and modeling of quasiperiodic diffraction patterns observed in equatorial VHF scintillation due to plasma bubbles

Quasiperiodic diffraction patterns have been observed in VHF scintillation recorded at Ascension Island in 1981. The patterns occur most often at the beginning or end of a scintillation patch and are shown to be consistent with those expected from irregularities having east-west scale sizes of a few hundred meters that are associated with the walls (edges) of equatorial plasma bubbles. By adjusting the geophysical parameters in a computer simulation of the amplitude fluctuations expected simultaneously at VHF, L-Band and C-Band, we model a specific event in detail. The model contains information on the size and strength of the structures that cause the regular fading patterns. In addition, multi-frequency diffraction patterns are computed for a 'phase screen' model based on high resolution measurements of a structured plasma bubble wall made using the AE-E satellite. The results are qualitatively very similar to the observations. Finally, implications of the model results for the extraction of information about the vertical structure of the irregularities are discussed.

Franke, S. J.↗
NASA NTRS1983

Interpretation of aircraft multispectral scanner images for mapping of alteration with uranium mineralization, Copper Mountain, Wyoming

NS-001 multispectral scanner data (0.45-2.35 micron) combined as principal components were utilized to map distributions of surface oxidation/weathering in Precambrian granitic rocks at Copper Mountain, Wyoming. Intense oxidation is found over granitic outcrops in partly exhumed pediments along the southern margin of the Owl Creek uplift, and along paleodrainages higher in the range. Supergene(?) uranium mineralization in the granites is localized beneath remnant Tertiary sediments covering portions of the pediments. The patterns of mineralization and oxidation are in agreement, but the genetic connections between the two remain in doubt.

Conel, J. E.↗
NASA NTRS1983

Interpretation of spectral optical thickness observations of the El Chichon eruption cloud

It is pointed out that the recent El Chichon eruption has provided a unique opportunity to observe a short-term climate change event. In October 1982 and in May 1983 observation experiments were undertaken to determine the spectral optical thickness of the El Chichon eruption cloud during airborne latitudinal surveys. One of two basic objectives to the observation experiment was the conduction of direct measurements of the optical thickness for radiation and climate studies. In connection with the second objective, inferences of the physical characteristic of the volcanic cloud were to be obtained on the basis of an application of remote sensing techniques. The present paper is concerned with the second objective, taking into account questions regarding the feasibility to conduct a meaningful analysis of the variation of the aerosol size distribution with latitude on the basis of the accuracy of the measured data.

Spinhirne, J. D.↗
NASA NTRS1984

Use of the TM tasseled cap transform for interpretation of spectral contrasts in an urban scene

Investigations are being conducted with the objective to develop automated numerical image analysis procedures. In this context, an examination is performed of physically-based multispectral data transforms as a means to incorporate a priori knowledge of land radiance properties in the analysis process. A physically-based transform of TM observations was developed. This transform extends the Landsat MSS Tasseled Cap transform reported by Kauth and Thomas (1976) to TM data observations. The present study has the aim to examine the utility of the TM Tasseled Cap transform as applied to TM data from an urban landscape. The analysis conducted is based on 512 x 512 subset of the Washington, DC November 2, 1982 TM scene, centered on Springfield, VA. It appears that the TM tasseled cap transformation provides a good means to explain land physical attributes of the Washington scene. This result provides a suggestion regarding a direction by which a priori knowledge of landscape spectral patterns may be incorporated into numerical image analysis.

Goward, S. N.↗
NASA NTRS1985

Interpretation of ozone temperature correlations. I - Theory

Correlations between ozone and temperature are commonly used to investigate the photochemical and dynamical aspects of satellite-derived ozone data. In this paper, the dynamical contributions to the ozone temperature correlations are examined using simple analytic and numerical models. It is shown that the phase differences between ozone and temperature waves caused by dynamical forcing can mimic the phase relationships predicted for photochemical equilibrium. Furthermore, the dynamical contribution to the phase relationship between ozone and temperature waves is routinely significant for chemistry time scales of approximately 0.5 days and is potentially important for time scales as short as 2 hours during stratospheric warmings. The model results are highly relevant to the analysis of the limb infrared monitor of the stratosphere and solar backscatter ultraviolet data taken during the winter of 1979.

Rood, R. B.↗