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At least 1,099 records · Page 61
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NASA NTRS1981

An airborne isothermal haze chamber

Thermal gradient diffusion cloud chambers (TGDCC) are used to determine the concentrations of cloud condensation nuclei (CCN) with critical supersaturations greater than or equal to about 0.2%. The CCN concentrations measured with the airborne IHC were lower than theoretically predicted by factors ranging between 7.9 and 9.0. The CCN concentrations measured with the airborne IHC were lower than the concentrations measured with the larger laboratory IHC's by factors ranging between 3.9 and 7.5. The bounds of the supersaturation ranges of the airborne IHC and the CSU-Mee TGDCC do not overlap. Nevertheless, the slopes of the interpolated data between the bounds agree favorably with the theoretical slopes.

Hindman, E. E.↗
NASA NTRS1981

Energy normalization of TV viewed optical correlation (automated correlation plane analyzer for an optical processor)

An automatic correlation plane processor that can rapidly acquire, identify, and locate the autocorrelation outputs of a bank of multiple optical matched filters is described. The read-only memory (ROM) stored digital silhouette of each image associated with each matched filter allows TV video to be used to collect image energy to provide accurate normalization of autocorrelations. The resulting normalized autocorrelations are independent of the illumination of the matched input. Deviation from unity of a normalized correlation can be used as a confidence measure of correct image identification. Analog preprocessing circuits permit digital conversion and random access memory (RAM) storage of those video signals with the correct amplitude, pulse width, rising slope, and falling slope. TV synchronized addressing of 3 RAMs permits on-line storage of: (1) the maximum unnormalized amplitude, (2) the image x location, and (3) the image y location of the output of each of up to 99 matched filters. A fourth RAM stores all normalized correlations. A normalization approach, normalization for cross correlations, a system's description with block diagrams, and system's applications are discussed.

Grumet, A.↗
NASA NTRS1981

A multi-frequency measurement of thermal microwave emission from soils: The effects of soil texture and surface roughness

An experiment on remote sensing of soil moisture content was conducted over bare fields with microwave radiometers at the frequencies of 1.4 GHz, 5 GHz, and 10.7 GHz during July - September of 1981. Three bare fields with different surface roughnesses and soil textures were prepared for the experiment. Ground truth acquisition of soil temperatures and moisture contents for 5 layers down to the depths of 15 cm was made concurrently with radiometric measurements. The experimental results show that the effect of surface roughness is to increase the soils' brightness temperature and to reduce the slope of regression between brightness temperature and moisture content. The slopes of regression for soils with different textures are found to be comparable, and the effect of soil texture is reflected in the difference of regression line intercepts at brightness temperature axis. The result is consistent with laboratory measurement of soils' dielectric permittivity. Measurements on wet smooth bare fields give lower brightness temperatures at 5 GHz than at 1.4 GHz.

Wang, J. R.↗
NASA NTRS1982

Improved global prediction of 300 nautical mile mean free air anomalies

Current procedures used for the global prediction of 300nm mean anomalies starting from known values of 1 deg by 1 deg mean anomalies yield unreasonable prediction results when applied to 300nm blocks which have a rapidly varying gravity anomaly field and which contain relatively few observed 60nm blocks. Improvement of overall 300nm anomaly prediction is first achieved by using area-weighted as opposed to unweighted averaging of the 25 generated 60nm mean anomalies inside the 300nm block. Then, improvement of prediction over rough 300nm blocks is realized through the use of fully known 1 deg by 1 deg mean elevations, taking advantage of the correlation that locally exists between 60nm mean anomalies and 60nm mean elevations inside the 300nm block. An improved prediction model which adapts itself to the roughness of the local anomaly field is found to be the model of Least Squares Collocation with systematic parameters, the systematic parameter being the slope b which is a type of Bouguer slope expressing the correlation that locally exists between 60nm mean anomalies and 60nm mean elevations.

Cruz, J. Y.↗
NASA NTRS1981

Interpretation of phase velocity measurements of wind-generated surface waves

Differences in experimental results for surface gravity wave phase speeds obtained by cross spectra and slope-height spectra are compared. It is shown that, for a simple two-dimensional model containing both dispersive and non-dispersive waves, the observed differences can be explained readily. The slope-height technique measures a weighted average of the wavenumber squared; for frequencies sufficiently large compared with the dominant frequency, the computed phase-speed variation with frequency is representative of the wave having the larger wavenumber - the dispersive wave. For the cross-spectral method, it is shown that the small-probe-separation assumption usually employed is not valid for frequencies much larger than the dominant frequency, except at the singular point where both waves have exactly equal spectral densities and the phase function represents an average of the two modes. For all other cases, the phase function approaches that of the wave having the larger spectral density, and essentially ignores the presence of the other wave, even if both modes are relatively close in their contributions to the total spectral density.

Dudis, J. J.↗
NASA NTRS1980

K/Ar dating of lunar soils. IV - Orange glass from 74220 and agglutinates from 14259 and 14163

Total fusion Ar-40 - A-39 analyses of orange glass from lunar soil 74220 combined with the sums of earlier stepwise heating data by other workers have yielded a precise K/Ar isochron with a slope corresponding to an age of 3.66 + or - 0.03 G.y. for the orange glass. The result is in marginal agreement with Huneke's (1978) age of 3.60 + or - 0.04 G.y. for 74220 glass. The Ar systematics in the agglutinates from 14259 and 14163 are dominated by volume correlated argon. Step-wise heating analyses yield data which define experimentally reproducible linear arrays in Ar-40/Ar-36 vs. K-40/Ar-36 diagrams. The slopes of these arrays correspond formally to very old ages, but it is not clear, however, that such ages have any physical significance.

Alexander, E. C., Jr.↗
NASA NTRS1982

A medium sensitivity X-ray survey using the Einstein Observatory - The log N-log S relation for extragalactic X-ray sources

The paper presents results of an X-ray survey of about 50 sq deg of the high galactic latitude sky at sensitivities in the range of 7 x 10 to the -14 to 5 x 10 to the -12 ergs/sq cm/s. The number-flux relation is derived for the extragalactic population to yield a best-fit power-law slope of 1.53 + or - 0.16, and the content of the sample is analyzed in terms of types of sources, appearing to be significantly different from the content of similar samples selected at higher fluxes. The medium sensitivity sample of extragalactic sources is dominated by active galactic nuclei, while samples selected at higher fluxes and higher energies are dominated by clusters of galaxies. Thus, the number-flux relation for extragalactic sources may be interpreted to a first approximation as the sum of the two different distributions with flatter and steeper slopes describing clusters and AGNs, respectively.

Maccacaro, T.↗
NASA NTRS1982

Radar scattering laws for the lunar surface

Bistatic radar observations of quasi-specular scatter from the lunar surface at 13 and 116 cm wavelengths have been expressed in terms of probability densities of the underlying surface slope distributions. These show best agreement with a Hagfors scattering function, although other forms having predominantly Gaussian or exponential characteristics also occur. Estimates of root mean square (rms) surface slope derived from these function range from 4 deg rms in maria to at least 8 deg rms in highlands. These are values appropriate to 25 m horizontal scales and represent averages over tens of square kilometers of surface area. The effective scattering roughness varies with wavelength, most strongly in maria, where its behavior is consistent with that expected from an immature, i.e., unsaturated cratered surface. There is very little variation in scattering roughness with wavelength in highlands area.

Simpson, R. A.↗
NASA NTRS1982

Effects of horizontal body casting on the baroreceptor reflex control of heart rate

The purpose of this study was to investigate the effects of long-term horizontal body position on baroreceptor reflex control of heart rate. Six male rhesus monkeys (6.2-9.4 kg) were given bolus injections of 4.0 microgram/kg, phenylephrine during each of the following conditions: awake, anesthetized (10 mg/kg ketamine HCl), and after beta-blockade (1 mg/kg propranolol HCl) before, 7, 14, and 28 days after being placed in a horizontal body cast. R-R interval vs. systolic arterial pressure was plotted, and the slope was determined by least-squares-fit linear regression. Baroreceptor slope was significantly reduced by 7 days of horizontal body position and remained attenuated throughout the 28-day restraint period both before and after beta-receptor blockade. These data are consistent with the thesis that prolonged exposure to a zero-gravity environment impairs autonomic reflex regulation of the cardiovascular system.

Billman, G. E.↗
NASA NTRS1981

Remote sensing of the ocean waveheight spectrum using synthetic-aperture-radar images

The paper discusses problems in the detection and measurement of ocean waves from their SAR images, in particular the measurement of the wavenumber spectrum of ocean-wave-height fluctuations. Comparisons on a limited set of pitch-roll buoy and SEASAT SAR measurements during the 1978 JASIN experiment reveal that degradation of SAR resolution caused by wave orbital motion is a crucial factor in the detection of waves by SAR images. Thus, waves with small slopes traveling perpendicular to the SAR flight path are more easily detected than waves with large slopes traveling along the flight path. Although the SAR estimates in this comparison were found to contain significant biases, they were in rough agreement with buoy measurements, provided the ocean wavelength was between about 120 and 400 m and the ocean wave direction was not approximately along the SAR flight path.

Vesecky, J. F.↗
NASA NTRS1983

Regression analysis of traction characteristics of traction fluids

Traction data for Santotrac 50 and TDF-88 over a wide range of operating conditions were analyzed. An eight term correlation equation to predict the maximum traction coefficient and a six term correlation equation to predict the initial slope of the traction curve were developed. The slope correlation was corrected for size effect considering the compliance of the disks. The effects of different operating conditions on the traction performance of each traction fluid were studied. Both fluids exhibited a loss in traction with increases in spin, but the losses with the TDF-88 fluid were not as severe as those with Santotrac 50. Overall, both fluids exhibited similar performance, showing an increase in traction with contact pressure up to about 2.0 GPa, and a reduction in traction with higher surface speeds up to about 100 m/sec. The apparent stiffness of the traction contact, that is, film disk combination, increases with contact pressure and decreases with speed.

Loewenthal, S. H.↗
NASA NTRS1983

On identifiability of flexible structure parameters

This report investigates the identifiability of modal parameters of flexible structures. Expressions are derived for Cramer-Rao lower bounds for the modal parameters, that is, frequencies, damping ratios and mode shapes or slopes. The optimal initial state, which maximizes the trace of the Fisher information matrix in the absence of persistent input, is obtained. The concepts discussed are applied to a finite-element model of the 122 meter hoop/column antenna. The numerical results show that the identifiability of the structural frequencies is excellent, followed by that of the damping ratios and the mode-slopes.

Joshi, S. M.↗
NASA NTRS1983

Influence of modulation frequency in rubidium cell frequency standards

The error signal which is used to control the frequency of the quartz crystal oscillator of a passive rubidium cell frequency standard is considered. The value of the slope of this signal, for an interrogation frequency close to the atomic transition frequency is calculated and measured for various phase (or frequency) modulation waveforms, and for several values of the modulation frequency. A theoretical analysis is made using a model which applies to a system in which the optical pumping rate, the relaxation rates and the RF field are homogeneous. Results are given for sine-wave phase modulation, square-wave frequency modulation and square-wave phase modulation. The influence of the modulation frequency on the slope of the error signal is specified. It is shown that the modulation frequency can be chosen as large as twice the non-saturated full-width at half-maximum without a drastic loss of the sensitivity to an offset of the interrogation frequency from center line, provided that the power saturation factor and the amplitude of modulation are properly adjusted.

Audoin, C.↗
NASA NTRS1981

Using radar image simulation to assess relative geometric distortions inherent in radar imagery

A unique method for observing the relative contributions of backscatter and propagation effects is afforded by radar image simulation. Digital terrain data are used in modeling radar image formation. Backscatter and propagation effects are modeled separately. These are incorporated serially and the image expression of each is noted. Sequences of images are presented illustrating these effects over a range of slopes and angles of incidence. The conclusions reached are that at angles of incidence that are smaller than the average slope of the terrain in a region, propagation phenomena predominate. As the angle of incidence increases beyond this, the radar image portrays an increasingly faithful representation of the backscatter from the ground. It is also demonstrated that digital simulation affords an important tool for evaluating complex interactions between the ground and radar, for training users in radar image interpretation, and for selecting optimum sensor parameters for particular applications.

Kaupp, V. H.↗
NASA NTRS1982

The effects of C, P, and S on trace element partitioning during solidification in Fe-Ni alloys

Trace and minor element distributions in the iron meteorites are generally ascribed to partitioning during solidification of the parent body core or to partial melting within the parent body. A model involving fractional crystallization is considered. The model cannot account for differences between the measured values for the slopes on the log Ir-log Ni plots and the slopes predicted using experimentally determined distribution coefficients obtained in an investigation conducted by Goldstein and Friel (1978). The model has also other weaknesses. Part of the answer concerning the existing problems was provided by Narayan and Goldstein (1981, 1982). The present investigation is concerned with a further clarification of the effect of the minor elements P, S, and C on the distribution behavior of trace elements. Attention is given to measurements of the distribution coefficients for various elements (Ir, Ge, Ga, Au, Cu, Cr) in the presence of these minor elements.

Willis, J.↗
NASA NTRS1983

Multifrequency measurements of the effects of soil moisture, soil texture, and surface roughness

An experiment on remote sensing of soil moisture content was conducted over bare fields with microwave radiometers at the frequencies of 1.4, 5, and 10.7 GHz, during July-September of 1981. Three bare fields with different surface roughnesses and soil textures were prepared for the experiment. The experimental results show that the effect of surface roughness is to increase the soil's brightness temperature and to reduce the slope of regression between brightness temperature and moisture content. The slopes of regression for soils with different textures are found to be comparable and the effect of soil texture is reflected in the difference of regression line intercepts at brightness-temperature axis. Measurements on wet smooth bare fields give lower brightness temperatures at 5 than at 1.4 GHz. This phenomenon is not expected from current radiative transfer theory, using laboratory measurements of the relationship between permittivity and moisture content for different soil-water mixtures at frequencies of not greater than 5 GHz.

Wang, J. R.↗
NASA NTRS1983

On one-dimensional stretching functions for finite-difference calculations

The class of one-dimensional stretching functions used in finite-difference calculations is studied. For solutions containing a highly localized region of rapid variation, simple criteria for a stretching function are derived using a truncation error analysis. These criteria are used to investigate two types of stretching functions. One an interior stretching function, for which the location and slope of an interior clustering region are specified. The simplest such function satisfying the criteria is found to be one based on the inverse hyperbolic sine. The other type of function is a two-sided stretching function, for which the arbitrary slopes at the two ends of the one-dimensional interval are specified. The simplest such general function is found to be one based on the inverse tangent. Previously announced in STAR as N80-25055

Vinokur, M.↗
NASA NTRS1983

The red edge of plant leaf reflectance

A detailed study of the red edge spectral feature of green vegetation based on laboratory reflectance spectrophotometry is presented. A parameter lambda is defined as the wavelength is defined as the wavelength of maximum slope and found to be dependent on chlorophyll concentration. Species, development stage, leaf layering, and leaf water content of vegetation also influences lambda. The maximum slope parameter is found to be independent of simulated ground area coverage. The results are interpreted in terms of Beer's Law and Kubelka-Munk theory. The chlorophyll concentration dependence of lambda seems to be explained in terms of a pure absorption effect, and it is suggested that the existence of two lambda components arises from leaf scattering properties. The results indicate that red edge measurements will be valuable for assessment of vegetative chlorophyll status and leaf area index independently of ground cover variations, and will be particularly suitable for early stress detection.

Horler, D. N. H.↗