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At least 397 records · Page 22

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NASA NTRS1987

Ionospheric electron-content measurements during the second space-plasma negative-ion experiment (SPINEX-2)

The second space-plasma negative-ion experiment (SPINEX-2), a chemical-release active experiment to investigate negative-ion effects in the ionospheric F region, is described by Mendillo et al. (1982). This paper describes the electron-content measurements in somewhat more detail than would be appropriate there. The circumstances of the experiment, particularly the use of a vehicle with a very high spin rate, presented some unusual challenges during interpretation of the electron-content data. These are described. The resulting profiles show clearly that the chemical release caused a very significant 'hole' in the ionosphere. Under certain fairly realistic assumptions, the actual number of free electrons removed from the region of the peak of the ionospheric F layer is estimated to be about 4 x 10 to the 25th. The same assumptions lead to a simple radial distribution of the depleted region about the rocket trajectory in the neighborhood of the release.

Fulford, J. A.↗

NASA NTRS1988

Estimating Electron Content Of The Ionosphere

Method for estimation total electron content of ionosphere. Based on measurements of signals transmitted from global positioning satellites (GPS's). Ionospheric delays obtained by measuring differential arrival times of signals at two different frequencies. Since GPS observations cover certain regions of sky, location of space probe to be calibrated might not overlap GPS field of view. Certain assumptions made about behavior of ionosphere so total electron content estimated in any direction from receiver.

Lanyi, G. E.↗

NASA NTRS1988

Remote sensing of forest canopy and leaf biochemical contents

Recent research on the remote sensing of forest leaf and canopy biochemical contents suggests that the shortwave IR region contains this information; laboratory analyses of dry ground leaves have yielded reliable predictive relationships between both leaf nitrogen and lignin with near-IR spectra. Attention is given to the application of these laboratory techniques to a limited set of spectra from fresh, whole leaves of conifer species. The analysis of Airborne Imaging Spectrometer data reveals that total water content variations in deciduous forest canopies appear as overall shifts in the brightness of raw spectra.

Peterson, David L.↗

NASA NTRS1988

Volatile/mobile trace elements in meteoritic, non-lunar basalts: Guides to Martian sample contents

A variety of genetic processes on or in extraterrestrial objects can be examined by study of volatile/mobile trace elements. Doubtless, considerable efforts will be expended on determining these elements in returned Martian samples. The purpose is to estimate levels of such elements expected to be present in returned Martian samples. Some ideas about Martian genesis were already advanced from the volatile/mobile element contents in SNC meteorites, assuming that Mars was their parent body. Even is Mars and the SNC meteorite parent body are identical, compositional ranges for returned Martian samples should exceed those of SNC meteorites. It is expected, therefore, that Martian samples returned from locations other than Polar regions will have indigenous volatile/mobile element contents within howardite-diogenite ranges. Elements with strong lithophile tendences may be more abundant, as they are in many lunar samples. Most of these elements should be at ppb levels except for Co, Ga, Zn, and Rb, which should lie at ppm levels. If Martian volcanism was accompanied by fumarolic emanations, it should be reflected in occasional huge enrichments of mobile trance elements, as in lunar meteorite Y 791197. During collection and transport Earthward, samples must be contained under conditions appropriate to ppb concentrations. Materials must be used that will not cause contamination which occurred during the Apollo program, where indium from seals contaminated many samples.

Lipschutz, M. E.↗

NASA NTRS1988

Observed effects of soil organic matter content on the microwave intensity of soils

In order to determine the significance of organic matter content on the microwave emissivity of soils when estimating soil moisture, field experiments were conducted in which 1.4 GHz microwave emissivity data were collected over test plots of sandy loam soil with different organic matter levels (1.8, 4.0, and 6.1 percent) for a range of soil moisture values. Analyses of the observed data show only minor variation in microwave emissivity due to a change in organic matter content at a given moisture level for soils with similar texture and structure. Predictions of microwave emissivity made using a dielectric model for aggregated soils exhibit the same trends and type of response as the measured data when appropriate values for the input parameters were utilized.

Jackson, T. J.↗

NASA NTRS1990

Experiment K-6-20. The effect of spaceflight on pituitary oxytocin and vasopressin content of rats

Pituitary levels of oxytocin (OT) and vasopressin (AVP) were measured in rats exposed to 12.5 days of spaceflight (FLT) as well as ground-based controls, one group synchronously maintained in flight-type cages with similar feeding schedules (SYN), and one group in vivarium cages (VIV). Flight rats had significantly less (p less than 0.05) pituitary OT and AVP(1.10 plus or minus 0.04 and 1.69 plus or minus 0.07 micron g, n=5) than either the SYN(1.60 plus or minus 0.08 and 2.11 plus or minus 0.04 micron g, n=5) or VIV (1.54 plus or minus 0.03 and 2.10 plus or minus 0.09 micron g, n=5) control groups, respectively. Because the FLT group mean body weight was significantly less (p less than 0.05) than either control group, the pituitary hormone content was also calculated on the basis of posterior pituitary protein content. When calculated in this manner, pituitary OT in the FLT rats (5.09 plus or minus 0.15 micron g/mg protein) was significantly less (p less than 0.05) than SYN(7.66 plus or minus 0.39 micron g/mg protein) or VIV controls (8.11 plus or minus 0.64 micron g/mg protein). Pituitary AVP was also less in the FLT animals (7.80 plus or minus 0.13 micron g/mg protein) compared to either SYN(9.84 plus or minus 0.51, p less than 0.05) or VIV controls (11.01 plus or minus 0.76, p less than 0.05). The reduced levels of pituitary OT and AVP may have resulted from increased hormone secretion resulting from the combined effects of water deprivation and the stress of the novel microgravity environment.

Keil, L.↗

NASA NTRS1990

Extraterrestrial halogen and sulfur contents of the stratosphere

Interplanetary dust represents a potential source of environmentally important chemical species in the earth's atmosphere. Previous studies have used computational models of atmospheric evolution of meteor debris to conclude that the steady-state stratospheric component of extraterrestrial matter is a small fraction of the total aerosol load. Observational data suggest such calculations may underestimate stratospheric residence times and, thus, concentrations. Two computational methods were employed here to obtain reasonable limits for the stratospheric contents of halogens and sulfur from extraterrestrial sources. The lower limit was based on the total stratospheric aerosol load and the relative influxes from interplanetary dust and tropospheric sources. The upper limit was obtained using a viscous settling method. These results suggest that the steady-state extraterrestrial influxes of halogens are minor compared to tropospheric sources but the sulfur input may be comparable to the present observed stratospheric content. Temporal enhancements in the meteoroid flux, such as passage through comet debris lanes or impact by large bodies, may produce significant chemical perturbations in the atmosphere.

Sutton, S. R.↗

NASA NTRS1989

Detection of changes in leaf water content using near- and middle-infrared reflectances

A method to detect plant water stress by remote sensing is proposed using indices of near-IR and mid-IR wavelengths. The ability of the Leaf Water Content Index (LWCI) to determine leaf relative water content (RWC) is tested on species with different leaf morphologies. The way in which the Misture Stress Index (MSI) varies with RWC is studied. On test with several species, it is found that LWCI is equal to RWC, although the reflectances at 1.6 microns for two different RWC must be known to accurately predict unknown RWC. A linear correlation is found between MSI and RWC with each species having a different regression equation. Also, MSI is correlated with log sub 10 Equivalent Water Thickness (EWT) with data for all species falling on the same regression line. It is found that the minimum significant change of RWC that could be detected by appying the linear regression equation of MSI to EWT is 52 percent. Because the natural RWC variation from water stress is about 20 percent for most species, it is concluded that the near-IR and mid-IR reflectances cannot be used to remotely sense water stress.

Hunt, E. Raymond, Jr.↗

NASA NTRS1990

Analysis of the origins and implications of the O-18 content of stratospheric water vapor

Factors influencing the O-18 content of stratospheric H2O are reviewed in order to provide a theoretical framework for the interpretation of measurements of this quantity, which are now becoming available. Depletions in O-18 of 5-10 percent in stratospheric H2O are expected based on the known correlation between that of D and O-18 in tropospheric H2O and observed measurements of large (typically 50 percent) depletions of D in stratosphere H2O. H2O formed in the stratosphere as a result of oxidation of CH4 can be expected to reflect primarily the O-18 content of stratospheric O2, which is the same as that of tropospheric O2 (slightly enhanced with respect to standard mean ocean water). Thus, a reduction in the O-18 depletion is expected with increasing altitude, but not a large enhancement in O-18 in upper stratospheric H2O as found in recent far infrared measurements. The observed large enhancement of O-18 in stratospheric O3 is not expected to be reflected in stratospheric H2O. Necessary laboratory data for the improved quantification of these effects are reviewed.

Kaye, Jack A.↗

NASA NTRS1990

Observed effects of soil organic matter content on the microwave emissivity of soils

O'Neill, P. E.↗

NASA NTRS1989

Spectral band selection for classification of soil organic matter content

This paper describes the spectral-band-selection (SBS) algorithm of Chen and Landgrebe (1987, 1988, and 1989) and uses the algorithm to classify the organic matter content in the earth's surface soil. The effectiveness of the algorithm was evaluated comparing the results of classification of the soil organic matter using SBS bands with those obtained using Landsat MSS bands and TM bands, showing that the algorithm was successful in finding important spectral bands for classification of organic matter content. Using the calculated bands, the probabilities of correct classification for climate-stratified data were found to range from 0.910 to 0.980.

Henderson, Tracey L.↗

NASA NTRS1990

Information content of interferometric delay-rate measurements for planetary orbiter navigation

Spacecraft such as Magellan and Mars Observer will use earth-based interferometric delay-rate tracking to meet their navigation requirements. Examples of methods used to implement these measurements are Differenced One-Way Doppler, delta-Differenced One-Way Doppler, and Two-Way Minus Three-Way Doppler. These measurements have a greater capability to observe certain orbital elements than that possessed by two-way Doppler, which has been the sole data type used in all U.S. planetary orbiter missions to date. In this paper, an approximate analytic model is developed for delay-rate measurements, as a function of classical orbital elements. The resulting expressions are used to show how the information content of these data types varies with orbit size, shape, and orientation. Comparison is made with the information content of Doppler data, using orbital element sets derived from the Magellan and Mars Observer missions. Results indicate that navigation accuracy improvements obtained by augmenting Doppler data with delay-rate measurements are greatest for spacecraft in low-altitude circular orbits; but decrease steadily for orbits of progressively greater size and eccentricity. The differences in Doppler-only and Doppler plus delay-rate orbit determination accuracies were also found to be highly dependent on Doppler measurement accuracy.

Thurman, Sam W.↗

NASA NTRS1991

Equilibrated moisture content of several carbon phenolics and their relationship to resin, fiber, and interface properties

This study focuses on the relationship between relative humidity and the equilibrated moisture content of several variants of two distinctly different carbon phenolic composites. One of the materials gives a typical exponential relationship between RH and equilibrated moisture content while the second gives an inverse sigmoidal relationship with the largest increase in moisture between 45-60 percent relative humidity. The possible relationship between the shape of the curves and the nature of the material constituents is discussed.

Stokes, E. H.↗

NASA NTRS1992

A system to measure flow moisture content in hypersonic wind tunnels

The technique and equipment is described which is used for obtaining data on the moisture content in two NASA Langley Hypersonic Wind Tunnels. A detailed description of the sampling system and its operation is presented along with the moisture analyzer used. The procedure used for converting dew point to parts of water per million by volume (ppmv) is included with graphs that show tunnel moisture content at various pressures.

West, James W.↗

NASA NTRS1991

Information content of polarimetric SAR data

The information content of the compressed Stoke's matrix data from the Airborne Synthetic Aperture Radar (AIRSAR) is examined in two ways - by measuring how each feature separates classes of terrain in an image, and by measuring how well a classifier performs with and without each feature. In this way, the features may then be ranked in order of information content (or in order of utility to the classifier). Suggestions are made regarding those variables that can be omitted in a data compression scheme or in a future simplified radar system.

Cumming, Ian G.↗

NASA NTRS1991

Lunar neutron leakage fluxes as a function of composition and hydrogen content

Areas of the moon that might have enhanced concentrations of hydrogen are discussed. The fluxes of thermal, epithermal, and fast neutrons escaping from the lunar surface were calculated for eight different compositions and several hydrogen contents. These flux ratios depend on composition and are very sensitive to the hydrogen content. Their measurement using flight-proven techniques from lunar orbit should allow detection and identification of hydrogen residing in either permanently shaded cold traps near the lunar poles or mature regoliths. Knowledge of composition, especially of Fe and Ti, improves the thresholds for hydrogen detection and also could allow identification of Gd and Sm.

Feldman, W. C.↗

NASA NTRS1992

Pituitary oxytocin and vasopressin content of rats flown on Cosmos 2044

Preliminary studies in rats (COSMOS 1887) suggested that levels of posterior pituitary hormones were reduced by exposure to spaceflight. To confirm these preliminary findings, pituitary tissue from rats flown for 14 days on Cosmos 2044 is obtained. Posterior pituitary content of oxytocin (OT) and vasopressin (VP) were measured in these tissues as well as those from ground-based controls. The synchronous control group had feeding and lighting schedules synchronized to those in the spacecraft and were maintained in flight-type cages. Another group was housed in vivarium cages; a third group was tail suspended (T), a method used to simulate microgravity. Flight rats showed an average reduction of 27 in pituitary OT and VP compared with the three control groups. When hormone content was expressed in terms of pituitary protein (microg hormone/mg protein), the average decrease in OT and VP for the flight animals ranged from 20 to 33 percent compared with the various control groups. Reduced levels of pituitary OT and VP were similar to preliminary measurements from the Cosmos 1887 mission and appear to result from exposure to spaceflight. These data suggest that changes in the rate of hormone secretion or synthesis may have occurred during exposure to microgravity.

Keil, L.↗

NASA NTRS1991

Effects of intra- and inter-laminar resin content on the mechanical properties of toughened composite materials

Composite materials having multiphase toughened matrix systems and laminate architectures characterized by resin-rich interlaminar layers (RIL) have been the subject of much recent attention. Such materials are likely to find applications in thick compressively loaded structures such as the keel area of commercial aircraft fuselages. The effects of resin content and its interlaminar and intralaminar distribution on mechanical properties were investigated with test and analysis of two carbon-epoxy systems. The RIL was found to reduce the in situ strengthening effect for matrix cracking in laminates. Mode 2 fracture toughness was found to increase with increasing RIL thickness over the range investigated, and Mode 1 interlaminar toughness was negligibly affected. Compressive failure strains were found to increase with increasing resin content for specimens having no damage, holes, and impact damage. Analytical tools for predicting matrix cracking of off-axis plies and damage tolerance in compression after impact (CAI) were successfully applied to materials with RIL.

Grande, Dodd H.↗