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At least 145 records · Page 8
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NASA NTRS1976

Isotopic abundances of Hg in mercury stars inferred from the Hg II line at 3984 A

Wavelengths of the Hg II absorption feature at 3984 A in 30 Hg stars are distributed uniformly from the value for the terrestrial mix to a value that corresponds to nearly pure Hg-204. The wavelengths are correlated loosely with effective temperatures inferred from Q(UBV). Relative isotopic abundances derived from partially resolved profiles of the 3984-A line in iota CrB, chi Lup, and HR 4072 suggest that mass-dependent fractionation has occurred in all three stars. It is supposed that such fractionation occurs in all Hg stars, and a scheme whereby isotopic compositions can be inferred from a comparison of stellar wavelengths and equivalent widths with those calculated for a family of fractionated isotopic mixes. Theoretical profiles calculated for the derived isotopic composition agree well with high-resolution interferometric profiles obtained for three of the stars.

White, R. E.↗
NASA NTRS1977

Particle motion on Mars inferred from the Viking lander cameras

Data from Viking lander cameras indicate fine particle mobility on the surface of Mars such as: probable ventifacts, rock-associated raised streaks, and particulate drifts. Peak wind directions inferred from Chryse and Utopia are roughly equal, and are consistant with those inferred by orbiter photography. A 24 deg systematic offset between: (1) the direction of rock-associated streaks in the Viking I landing site, and (2) Mariner 9 and Viking observations of crater-associated streaks is consistant with a Coriolis acceleration of particles entrained by high-velocity winds during the production of crater-associated streaks. It is suggested that if a large fraction of collision impact energy goes into deformation, strain, and rupture, a preferential destruction of the most easily saltated grains and a depletion of 15-micron diameter grains will be observed. Investigations of particulates dumped on the landing grid suggest that major saltation events took place between sols 96 and 207, caused by winds of greater than 50 meters/sec normalized to the top of the boundary layer.

Sagan, C.↗
NASA NTRS1978

The EUV flux inferred from AE-C He/+/ abundances

The ionization rate of helium in the thermosphere is inferred from He(+) abundances determined by instrumentation on the Atmosphere Explorer-C satellite. The inferred ionization rate is independent of the particular geophysical parameters of the thermosphere for solar zenith angles less than 80 deg and altitudes between 280 and 360 km. The ionization rate is consistent with a value calculated from the EUV flux of Hinteregger (1976) below 504 A.

Oppenheimer, M.↗
NASA NTRS1979

Remote sensing of seasonal distribution of precipitable water vapor over the oceans and inference of boundary layer structure

Over the ocean satellite infrared spectral measurements in the 18 micrometer water vapor band and the 11 micrometer window region were used to derive precipitable water vapor, w, in the atmosphere and the sea surface temperature, SST. Seasonal maps of w on the oceans derived from these data reveal the dynamical influence of the large scale atmospheric circulation. With the help of a model for the vertical distribution of water vapor, the configuration of the atmospheric boundary layer over the oceans can be inferred from w when the information of SST is combined. The gross seasonal mean structure of the boundary layer inferred in this fashion reveals the broad areas of the trade wind inversion and the convectively active areas such as the intertropical convergence zones.

Prabhakara, C.↗
NASA NTRS1979

Plausible inference: A multi-valued logic for problem solving

A new logic is developed which permits continuously variable strength of belief in the truth of assertions. Four inference rules result, with formal logic as a limiting case. Quantification of belief is defined. Propagation of belief to linked assertions results from dependency-based techniques of truth maintenance so that local consistency is achieved or contradiction discovered in problem solving. Rules for combining, confirming, or disconfirming beliefs are given, and several heuristics are suggested that apply to revising already formed beliefs in the light of new evidence. The strength of belief that results in such revisions based on conflicting evidence are a highly subjective phenomenon. Certain quantification rules appear to reflect an orderliness in the subjectivity. Several examples of reasoning by plausible inference are given, including a legal example and one from robot learning. Propagation of belief takes place in directions forbidden in formal logic and this results in conclusions becoming possible for a given set of assertions that are not reachable by formal logic.

Friedman, L.↗
NASA NTRS1978

The simultaneous inference of stratospheric trace gases with overlapping spectral signatures using limb sounding radiometry

An inversion algorithm has been developed to simultaneously infer the concentrations of two gases with overlapping spectral signatures using limb emission measurements. The algorithm is efficient and provides a solution in two or three iterations. It has been applied in a simulation study to the inference of stratospheric NO2-H2O and HNO3-CF2Cl2. Existing satellite instrumentation was the basis for errors used in the calculations. It is estimated that concentrations of all four gases can be determined with errors of about 20 percent. This assumes an estimated 1980 CF2Cl2 level. Also, other error sources due to contaminant gas, aerosol emission, and the temperature profile must be included to obtain a better estimate of experimental accuracies.

Russell, J. M., III↗
NASA NTRS1979

Remote sensing of seasonal distribution of precipitable water vapor over the oceans and the inference of boundary-layer structure

From the depth of the water vapor spectral lines in the 8-9 micron window region, measured by the Nimbus 4 Infrared Interferometer Spectrometer (IRIS) with a resolution of about 3/cm, the precipitable water vapor over the oceans is remotely sensed. In addition the IRIS spectral data in the 11-13 micron window region have been used to derive the sea surface temperature (SST). Seasonal maps of w on the oceans deduced from the spectral data reveal the dynamical influence of the large-scale atmospheric circulation. With the help of a model for the vertical distribution of water vapor, the configuration of the atmospheric boundary layer over the oceans can be inferred from these remotely sensed w and SST. The gross seasonal mean structure of the boundary layer inferred in this fashion reveals the broad areas of trade wind inversion and the convectively active areas such as the ITCZ. The derived information is in reasonable agreement with some observed climatological patterns over the oceans.

Prabhakara, C.↗
NASA NTRS1979

The simultaneous inference of stratospheric NO2-H2O and HNO3-CF2Cl2 using limb sounding radiometry

An inversion algorithm has been developed to simultaneously infer the concentrations of two gases with overlapping spectral signatures using limb emission measurements. The algorithm provides a solution in two or three iterations and has been tested in a simulation study for the inference of stratospheric NO2-H2O and HNO3-CF2Cl2. Existing satellite instrumentation was the basis for errors used in the calculations. These included noise, scale and bias errors, angular registration errors, spacecraft motion effects, and effects due to a finite instrument field of view. It is estimated that concentrations of all four gases can be measured globally from a satellite with errors of less than 20%.

Russell, J. M., III↗
NASA NTRS1981

A satellite investigation of energy flux and inferred potential drop in auroral electron energy spectra

Because predicted relationship (epsilon directly varies with V squared) between auroral electron energy flux (epsilon) and the inferred acceleration potential drop (V) for accelerated Maxwellian distributions was favorably tested by other using sounding rocket data for the limiting case of eVE 1 (where Ec is the characteristic energy of the accelerated Maxwellian distribution) and for a single inverted-V observed by the Injun 5 satellite, data from Atmosphere D were used to extend these studies over the range .2 eV/Ec 5 and for a wide range of latitudes and local times on both the nightside and the dayside. Results show good agreement with the full accelerated Maxwellian model. An analytical approximation to the electron energy flux was derived which better describes the data over the range .2 eV/Ec approximated 3. Analyses of individual energy spectra at small and large pitch angles through well-defined inverted-V structures suggest that the altitude of the inferred potential drop maximizes near the center of the inverted-V's.

Meniett, J. D.↗
NASA NTRS1981

Information theory lateral density distribution for Earth inferred from global gravity field

Information Theory Inference, better known as the Maximum Entropy Method, was used to infer the lateral density distribution inside the Earth. The approach assumed that the Earth consists of indistinguishable Maxwell-Boltzmann particles populating infinitesimal volume elements, and followed the standard methods of statistical mechanics (maximizing the entropy function). The GEM 10B spherical harmonic gravity field coefficients, complete to degree and order 36, were used as constraints on the lateral density distribution. The spherically symmetric part of the density distribution was assumed to be known. The lateral density variation was assumed to be small compared to the spherically symmetric part. The resulting information theory density distribution for the cases of no crust removed, 30 km of compensated crust removed, and 30 km of uncompensated crust removed all gave broad density anomalies extending deep into the mantle, but with the density contrasts being the greatest towards the surface (typically + or 0.004 g cm 3 in the first two cases and + or - 0.04 g cm 3 in the third). None of the density distributions resemble classical organized convection cells. The information theory approach may have use in choosing Standard Earth Models, but, the inclusion of seismic data into the approach appears difficult.

Rubincam, D. P.↗
NASA NTRS1981

A satellite investigation of energy flux and inferred potential drop in auroral electron energy spectra

The relationship between auroral electron energy flux and the inferred accelerating potential drop for accelerated Maxwellian distributions is investigated on the basis of Atmospheric Explorer D spectral measurements. An analytical approximation for the total downward energy flux carried by an isotropic Maxwellian electron population accelerated by a field-aligned electrostatic potential drop is derived which is valid for values of the electron energy/characteristic accelerated Maxwellian distribution energy which are less than the difference between the ratio of the magnetic field strengths at the altitude of observation and the altitude of potential drop, and unity. Data from the Low Energy Electron Experiment on board AE D obtained on both the dayside and the nightside during periods of significant inverted-V type electron precipitation shows that the 455 energy spectra considered, 160 of them, obtained between 60 and 85 deg invariant latitude, could be fit to accelerated Maxwellian distributions. The 160 Maxwellian spectra are then shown to be in agreement with the predictions of the accelerated Maxwellian model. Finally, analysis of individual spectra suggests that the altitude of the inferred potential drop is at a maximum near the center of the inverted-V structures.

Menietti, J. D.↗
NASA NTRS1981

The feasibility of using time-dependent photochemical calculations to infer radical species concentrations from solar occultation absorption measurements

In connection with fast chemical reactions, short-lived stratospheric species experience rapid concentration variations at sunset and sunrise. For solar occultation absorption measurements, these rapid concentration variations may introduce significant errors with respect to the inference of atmospheric abundances for some species due to asymmetrical concentration distributions. Most retrieval algorithms assume that concentration distributions are spherically symmetric. The effect of this assumption on the accuracy of inferred concentrations has been studied by Kerr et al. (1977). The present investigation considers the feasibility of using a time-dependent one-dimensional photochemical model to provide detailed information about the asymmetrical distribution for use in the retrieval procedure. As shown by Boughner et al. (1980), diurnal effects can be represented by an inhomogeneity factor. It is found that the NO retrieval improves considerably with the inclusion of a correction factor containing the asymmetrical variations.

Larsen, J. C.↗
NASA NTRS1985

Inference of high-latitude ionization and conductivity from AE-C measurements of auroral electron fluxes

Electron fluxes in the kilovolt energy range measured by the AE-C satellite have been used to infer the latitudinal distribution of ionization at high latitudes in the altitude range 90 to 200 km. These distributions are compared with simultaneous measurements of electron density by the Chatanika incoherent scatter radar. The study was based on more than 120 electron density profiles obtained on three different nights at magnetic local times between 0200 and 0400. The calculated distributions agree very well with the altitude and latitude distributions measured by the radar. The only obvious difference was the presence in the radar data of additional ionization produced by solar illumination. A comparison was also conducted of the height-integrated electrical conductivities computed from the measured profiles and those inferred from the satellite measurements. For Hall and Pedersen conductances greater than 5 mhos, the agreement is within 25 percent. The data were also used to deduce the altitude profile of the effective recombination coefficient. This profile agrees well with the results of previous studies.

Vondrak, R.↗
NASA NTRS1986

Comparison of regional clear-sky albedos inferred from satellite observations and model computations

A comparison of model- and satellite-inferred clear sky top-of-atmosphere (TOA) albedos is presented. The clear sky albedos were inferred from GOES-2 observations for November 1978 over South America and most of North America and adjacent ocean regions. The model albedos were computed on a 1 deg X 1 deg latitude-longitude grid, allowing for variations in surface vegetation type, solar zenith angle, orography, and spectral absorption/scattering. Over the ocean areas, the observed and calculated TOA albedos agree within + or - 1 percent, while the albedos over land mostly agree within + or - 2 percent for the entire range of significant geographical variation of albedo from 13 percent over the Amazon Basin to 24 percent over mountains of western North America. Both the ocean and land agreements lie within the theoretical and observational uncertainties.

Briegleb, B. P.↗
NASA NTRS1985

LIMS data - Inferred stratospheric distribution of NOx and HOx trace constituents and the calculated odd nitrogen budget

LIMS, SAMS, SBUV and in-situ data have been used to infer species not measured but which are of photochemical interest, e.g., O(3P), O(1D), NO, N2O5, OH, HO2, ClO and HCl. (LIMS = limb infrared monitor of the stratosphere; SAMS = stratospheric and mesospheric sounder; and SBUV = solar backscattered ultraviolet instrument.) Production and loss of odd nitrogen have been calculated and estimates have been made of the odd nitrogen transport due to adiabatically driven circulation derived from LIMS data. Data used from LIMS include O3, NO2, HNO3, H2O and T. CH4 and N2O were taken from SAMS and the UV solar flux from the SBUV instrument. Species were inferred for periods in October, December, March and May. Results for December are discussed. Results indicate: (1) maximum stratospheric odd nitrogen levels of 25 ppbv; (2) evidence of odd nitrogen transport from the mesosphere appearing at 25 km in the wintertime polar latitudes; (3) the polar night build-up of high levels of N2O5 beginning after the autumnal equinox; and (4) the possibility of large downward fluxes of odd nitrogen into the troposphere during the winter at latitudes poleward of 60 degrees.

Callis, L. B.↗
NASA NTRS1986

The Comet Giacobini-Zinner magnetotail: Axial stresses and inferred near-nucleus properties

Utilizing the electron and magnetic field data from the ICE tail traversal of comet Giacobini-Zinner along with the MHD equations, a steady state, stress balance model of the cometary magnetotail was developed, and used to infer important but unmeasured ion properties within the magnetotail at ICE and upstream at the average point along each streamline where cometary ions are picked-up. The derived tailward ion flow speed at ICE is quite constant at approx. -20 to -30 km/sec across the entire tail. The flow velocity, ion temperature, density, and ion source rates upstream from the lobes (current sheet) at the average pick-up locations are approx. -75 km/sec (approx. -12), approx. 4 million K (approx. 100,000), approx. 20 cc (approx. 400), and approx. 15 cu cm/sec. Gradients in the plasma properties between the two regions are quite strong. Implications of inferred plasma properties for the near-nucleus region and for cometary magnetotail formation are examined.

Mccomas, D. J.↗
NASA NTRS1986

The effect of local advection on the inference of soil moisture from thermal infrared radiances

The degree to which the GOES-VISSR infrared data can be used to infer area-averaged soil moisture is explored for a five-day case study period. Chosen variables are transformed and incorporated into a multiple linear regression. The actual observations, rather than a simplified model, are used to determine the relationship between soil moisture and GOES-IR radiance. It is shown that a depletion coefficient of 0.92 produces an index of ground truth which is best correlated with soil moisture as inferred from GOES thermal infrared data. When all individual daily soil estimates during the case study period are averaged at each point and compared to the average observed soil moisture, the data correlate at 0.85. This implies that the algorithm can distinguish at least four categories of soil moisture.

Wetzel, Peter J.↗
NASA NTRS1986

The design and application of a Transportable Inference Engine (TIE1)

A Transportable Inference Engine (TIE1) system has been developed by the author as part of the Interactive Experimenter Planning System (IEPS) task which is involved with developing expert systems in support of the Spacecraft Control Programs Branch at Goddard Space Flight Center in Greenbelt, Maryland. Unlike traditional inference engines, TIE1 is written in the C programming language. In the TIE1 system, knowledge is represented by a hierarchical network of objects which have rule frames. The TIE1 search algorithm uses a set of strategies, including backward chaining, to obtain the values of goals. The application of TIE1 to a spacecraft scheduling problem is described. This application involves the development of a strategies interpreter which uses TIE1 to do constraint checking.

Mclean, David R.↗