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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Coherent 1-micron lidar measurements of atmospheric-turbulence-induced spatial decorrelation using a multielement heterodyne detector array

A coherent 1-micron Nd:YAG lidar system is employed to measure directly the reduced spatial coherence length rho 0 of the lidar returns caused by atmospheric turbulence. The experiments were conducted by using a 2 x 2 heterodyne detector array, which permitted real-time spatial correlation measurements of the lidar returns at two different detector spacings. The spatial correlation coefficients and spatial coherence length of the lidar returns from a hard target were measured during a day-to-night time period when the atmospheric turbulence parameter, Cn-squared, was measured to vary from 2 x 10 exp -13 to 2 x 10 exp -4 m exp -2/3. These directly measured values of rho 0 as a function of Cn-squared were found to be in good agreement with theoretical predictions.

Chan, Kin P.↗
NASA NTRS1990

Immunoreactive prohormone atrial natriuretic peptides 1-30 and 31-67 - Existence of a single circulating amino-terminal peptide

Sep-Pak C18 extraction of human plasma and radioimmunoassay using antibodies which recognize atrial natriuretic peptide (99-128) and the prohormone sequences 1-30 and 31-67 resulted in mean values from 20 normal subjects of 26.2 (+/- 9.2), 362 (+/- 173) and 368 (+/- 160) pg/ml, respectively. A high correlation coefficient between values obtained using antibodies recognizing prohormone sequences 1-30 and 31-67 was observed (R = 0.84). Extracted plasma immunoreactivity of 1-30 and 31-67 both eluted at 46 percent acetonitrile. In contrast, chromatographic elution of synthetic peptides 1-30 and 31-67 was observed at 48 and 39 percent acetonitrile, respectively. Data suggest that the radioimmunoassay of plasma using antibodies recognizing prohormone sequences 1-30 and 31-67 may represent the measurement of a unique larger amino-terminal peptide fragment containing antigenic sites recognized by both antisera.

Chen, Yu-Ming↗
NASA NTRS1992

LDA measurements in a Mach 2 flow over a rearward facing step with staged transverse injection

Measurements of the mean velocity field and selected turbulence statistics have been obtained via 2D LDA in a Mach 2 flow over a rearward facing step with downstream transverse injection. Axial mean velocity profiles, profiles of the axial and normal RMS levels, and the correlation coefficient between the axial and normal fluctuating components are presented for locations upstream of the step. These data, through comparison with other reported measurements in zero pressure gradient compressible boundary layers indicate that the boundary layers upstream of the step are consistent with 'quasi-equilibrium' turbulent boundary layers with the adiabatic wall boundary condition. Mean velocity field measurements on the symmetry plane of the tunnel are compared to laser induced iodine fluorescence measurements reported in the literature and obtained in the same facility. This comparison demonstrates the quality of the present LDA data set and shows that particle lag is not significant in the LDA measurements despite the complex nature of the downstream flow.

Wang, J.-A.↗
NASA NTRS1990

Scattering from randomly oriented scatterers with strong permittivity fluctuations

Strong permittivity fluctuation theory is used to solve the problem of scattering from a medium composed of completely randomly oriented scatterers under a low frequency limit. Gaussian statistics are not assumed for the renormalized scattering sources. Numerical results on effective permittivity are illustrated for oblate and prolate spheroidal scatterers and compared with the results for spherical scatterers. The results are consistent with discrete scatterer theory. The effective permittivity of a random medium embedded with nonspherical scatterers shows a higher imaginary part than the spherical scatterer case with equal correlation volume. Under the distorted Born approximation, the polarimetric covariance matrix for the backscattered electric field is calculated for half-space randomly oriented scatterers. The nonspherical geometry of the scatterers shows significant effects on the cross-polarized backscattering returns, and the correlation coefficient between HH and VV returns. The polarimetric backscattering coefficients can provide useful information in distinguishing the geometry of scatterers.

Yueh, S. H.↗
NASA NTRS1992

Effects of surface baroclinicity on frontal overrunning along the central Gulf coast

Along the United States Gulf coast and over the northern Gulf of Mexico, frontal overrunning occurs frequently. Cyclogenesis over the Gulf is often associated with this type of weather system. Effects of baroclinic fields on frontal overrunning are investigated from synoptic and climatological points of view. It is found that, from October through April, the orientation of the shelf break is a very important baroclinic characteristic because fronts tend to stall there rather than at the physical coastline. To further substantiate this deduction dynamically, the local geostrophic vorticity field over the western Louisiana-upper Texas shelf region is estimated monthly. The correlation coefficient between the vorticity field and the frequency of frontal overrunning along the central Gulf coast was 0.86. For forecasting applications, a simple formula is provided to estimate this local vorticity from the temperature difference between Lake Charles, Louisiana, and buoy station 42002 in the deep Gulf.

Hsu, S. A.↗
NASA NTRS1992

Probabilistic finite elements for fatigue and fracture analysis

Attenuation is focused on the development of Probabilistic Finite Element Method (PFEM), which combines the finite element method with statistics and reliability methods, and its application to linear, nonlinear structural mechanics problems and fracture mechanics problems. The computational tool based on the Stochastic Boundary Element Method is also given for the reliability analysis of a curvilinear fatigue crack growth. The existing PFEM's have been applied to solve for two types of problems: (1) determination of the response uncertainty in terms of the means, variance and correlation coefficients; and (2) determination the probability of failure associated with prescribed limit states.

Belytschko, Ted↗
NASA NTRS1976

The Correlation of Active and Passive Microwave Outputs for the Skylab S-193 Sensor

This paper presents the results of the correlation analysis of the Skylab S-193 13.9 GHz Radiometer/Scatterometer data. Computer analysis of the S-193 data shows more than 50 percent of the radiometer and scatterometer data are uncorrelated. The correlation coefficients computed for the data gathered over various ground scenes indicates the desirability of using both active and passive sensors for the determination of various Earth phenomena.

Krishen, K.↗
NASA NTRS1993

Distribution of photons in squeezed polymode light

The distribution functions of photons in squeezed and correlated light for one-mode and multimode cases are obtained based on the method of integrals of motion. Correlation coefficient and squeezing parameter are calculated. The possibility to generate squeezed light using nonstationary Casimir effect is discussed. Quantum parametric Josephson junction is proposed as quantum vacuum generator of electrical vibrations.

Manko, V. I.↗
NASA NTRS1992

Lower stratosphere waves during 1986-1989 southern springs

Global NMC height analyses and Nimbus 7 TOMS Grid-T Version 6 data are used to investigate the horizontal structure of ozone and 50-mb height waves for the 1986-1989 springs of the Southern Hemisphere. Empirical orthogonal functions (EOFs) are obtained for the ozone and height data independently to identify the meridional structure of observed long waves as well as their propagation characteristics. The leading EOFs for both the ozone and 50-mb height waves exhibit wavenumber 1 and 2 patterns. The correlation coefficients between ozone and 50-mb height principal components are high. They indicate high/low ozone values associated with high/low values of 50-mb heights. This distribution is consistent with the advection of ozone by planetary waves south of the ozone maximum, as shown by a simple linear wave model. The observed total ozone amplitudes for waves 1 and 2 for most years are consistent with the total ozone predictions by the wave model.

Nogues-Paegle, Julia↗
NASA NTRS1992

Active and passive microwave measurements of soil moisture in FIFE

During the intensive field campaigns of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) in May-October of 1987, several nearly simultaneous measurements were made with low-altitude flights of the L-band radiometer and C- and X-band scatterometers over two transects in the Konza Prairie Natural Research Area, some 8 km south of Manhattan, Kansas. These measurements showed that although the scatterometers were sensitive to soil moisture variations in most regions under the flight path, the L-band radiometer lost most of its sensitivity in regions unburned for many years. The correlation coefficient derived from the regression between the radar backscattering coefficient and the soil moisture was found to improve with the increase in antenna incidence angle. This is attributed to a steeper falloff of the backscattering coefficient as a function of local incidence at angles near nadir than at angles greater than 30 deg.

Wang, J. R.↗
NASA NTRS1993

Excitation of earth's polar motion by atmospheric angular momentum variations, 1980-1990

We compute the polar-motion excitation function due to the atmospheric angular momentum (AAM) for both IB (inverted-barometer) and non-IB cases, as well as the excitation function from geodetically observed Earth orientation data for the period 1980-1990. The two are then compared in studying the AAM contribution to the polar motion excitation. The polar drifts with periods longer than about two years have similar characteristics, but the comparison is inconclusive because of data uncertainties. For the seasonal wobble excitation, the agreement is poor except for the prograde annual wobble, indicating the influence of other geophysical excitations than AAM. For the Chandler wobble excitation, a correlation coefficient of 0.53 for non-IB and 0.58 for IB are found for 1986-1990. Together with a coherence spectral analysis, they clearly demonstrate a strong contribution of AAM to the Chandler wobble excitation.

Chao, Benjamin F.↗
NASA NTRS1993

Sea surface height variability during 1986-1988 in the tropical Pacific Ocean

A description of the sea surface height variabilities during 1986-1988 in the tropical Pacific Ocean is presented on the basis of Geosat altimeter data and a tropical Pacific Ocean GCM (OGCM) forced with observed winds from Florida State University. Both data sets are validated against in situ sea-level measurements at 12 selected sea-level stations in the equatorial Pacific and were found to be in good agreement with these measurements with correlation coefficients of 0.69 for Geosat and 0.71 for OGCM. The Geosat altimeter data are capable of describing sea surface height variabilities during 1986-1988 in the tropical Pacific, in particular, the seasonal cycle, the 1987 El Nino and 1988 La Nina episodes, and the December 1986 equatorial Kelvin wave event. The OGCM-simulated surface dynamic height is found to be sensitive to different surface wind products.

Chao, YI↗
NASA NTRS1992

Estimation and analysis of interannual variations in tropical oceanic rainfall using data from SSM/I

Rainfall over tropical ocean regions, particularly in the tropical Pacific, is estimated using Special Sensor Microwave/Imager (SSM/I) data. Instantaneous rainfall estimates are derived from brightness temperature values obtained from the satellite data using the Hughes D-Matrix algorithm. Comparisons with other satellite techniques are made to validate the SSM/I results for the tropical Pacific. The correlation coefficients are relatively high for the three data sets investigated, especially for the annual case.

Berg, Wesley↗
NASA NTRS1993

Statistical temperature profile retrievals in clear-air using passive 118-GHz O2 observations

The clean-air temperature profile accuracy yielded by a localized linear statistical retrieval operator applied to passive aircraft-based 118-GHz spectra is demonstrated. A comparison of the statistically and physically derived correlation coefficients of antenna temperature and kinetic temperature furnishes a physical justification of the statistical retrieval technique. The atmospheric temperature mean and covariance significantly depend on such geophysical parameters as latitude, longitude, local season, and time, as well as the prevailing meteorological state and orographic effects.

Gasiewski, A. J.↗
NASA NTRS1993

On the relationship between thermal emissivity and the Normalized Difference Vegetation Index for natural surfaces

The spatial variation of both the thermal emissivity (8-14 microns) and Normalized Difference Vegetation Index (NDVI) was measured for a series of natural surfaces within a savanna environment in Botswana. The measurements were performed with an emissivity-box and with a combined red and near-IR radiometer, with spectral bands corresponding to NOAA/AVHRR. It was found that thermal emissivity was highly correlated with NDVI after logarithmic transformation, with a correlation coefficient of R = 0.94. This empirical relationship is of potential use for energy balance studies using thermal IR remote sensing. The relationship was used in combination with AVHRR (GAC), AVHRR (LAC), and Landsat (TM) data to demonstrate and compare the spatial variability of various spatial scales.

Van De Griend, A. A.↗
NASA NTRS1992

Phase difference statistics related to sensor and forest parameters

The information content of ordinary synthetic aperture radar (SAR) data is principally contained in the radiometric polarization channels, i.e., the four Ihh, Ivv, Ihv and Ivh backscattered intensities. In the case of clutter, polarimetric information is given by the four complex degrees of coherence, from which the mean polarization phase differences (PPD), correlation coefficients or degrees of polarization can be deduced. For radiometric features, the polarimetric parameters are corrupted by multiplicative speckle noise and by some sensor effects. The PPD distribution is related to the sensor, speckle and terrain properties. Experimental results are given for the variation of the terrain hh/vv mean phase difference and magnitude of the degree of coherence observed on bare soil and on different pine forest stands.

Lopes, A.↗
NASA NTRS1993

A study of the influence of satellite data on GLA analyses over the Atlantic Ocean during a period of blocking anticyclone development

This paper presents a statistical diagnosis of the differences between two Goddard Laboratory for Atmospheres analysis representations of temperature and wind speed, one containing satellite data influences (SAT analyses) and one without (NOSAT analyses), for a case of oceanic blocking anticyclone development. Results, obtained using area means and standard deviations of the two fields and correlation coefficients and root-mean-square differences between the two fields, indicate that the inclusion of satellite data can have significant impact on ocean-domain analyses. This is especially evident if one examines higher-order fields that represent gradients in the basic variable fields or contain covariances between two different variables (e.g., advections). More specifically, the inclusion of satellite data resulted in a cold (warm) temperature bias at low (high) levels and weaker temperature gradients, stronger winds, weaker vertical wind shears, and a warm-air advection bias at most levels. The SAT analyses also exhibited larger standard deviations than the NOSAT for wind speed, relative vorticity, vorticity advection, temperature advection, and 500-mb height tendencies, suggesting that for this case the spatial variability of the circulation features were enhanced by the inclusion of satellite data. Even so, since height tendencies forced by vorticity and temperature advection were less sensitive to the addition of satellite data than were the advection quantities themselves, the dynamics of the blocking system was apparently less influenced by the presence of satellite data than was the structure of the system.

Lamberty, Gregory L.↗
NASA NTRS1956

Propagation of a Free Flame in a Turbulent Gas Stream

Effective flame speeds of free turbulent flames were measured by photographic, ionization-gap, and photomultiplier-tube methods, and were found to have a statistical distribution attributed to the nature of the turbulent field. The effective turbulent flame speeds for the free flame were less than those previously measured for flames stabilized on nozzle burners, Bunsen burners, and bluff bodies. The statistical spread of the effective turbulent flame speeds was markedly wider in the lean and rich fuel-air-ratio regions, which might be attributed to the greater sensitivity of laminar flame speed to flame temperature in those regions. Values calculated from the turbulent free-flame-speed analysis proposed by Tucker apparently form upper limits for the statistical spread of free-flame-speed data. Hot-wire anemometer measurements of the longitudinal velocity fluctuation intensity and longitudinal correlation coefficient were made and were employed in the comparison of data and in the theoretical calculation of turbulent flame speed.

Mickelsen, William R↗