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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Vermont Wildland Fires: Investigating the Role of Antecedent Conditions and Recent Environmental Trends in Exacerbating Fire Risk and Potential in Vermont

Under a changing climate, increases in dry conditions and extreme heat events are projected to exacerbate wildfire risk in the northeastern U.S. In recent years, Vermont has observed higher annual temperatures, more frequent heatwaves, increased annual precipitation, extreme flood events, and decreased snowfall. The mechanisms through which environmental factors contribute to increased fire risk in humid environments, such as Vermont, are poorly understood. The team partnered with the National Weather Service, the Vermont Division of Forests, and the University of Vermont to investigate phenological trends and antecedent conditions influencing wildland fire risk. For the phenological analysis, from 2001 to 2023, vegetation data, phenological dates, and snow water equivalent (SWE) values were accessed from Landsat 5Thematic Mapper (TM), Landsat 7Enhanced Thematic Mapper Plus (ETM+), Landsat 8Operational Land Imager (OLI), Landsat 9OLI-2, the Moderate Resolution Imaging Spectroradiometer (MODIS), and the Snow Data Assimilation System (SNODAS), respectively. For the antecedent condition analysis, from 2008 to 2023, soil moisture, Environmental Stress Index, wind speed, minimum relative humidity, and daily precipitation data were obtained from the Global Land Data Assimilation System (GLDAS), SERVIR, gridMET Wind, gridMET Humidity, and NClimGrid, respectively. The study found that green-up dates over the study period remain relatively stable, while snowmelt dates appear increasingly variable. Minimum relative humidity was the most significant environmental variable correlated with wildfire risk in Vermont. Results from this study will inform the National Weather Service's preparation of fire forecasts before prescribed burns and support community outreach by the Vermont Agency of Natural Resources.

Wildland Fire↗
NASA NTRS1975

Light and dark soils at the Apollo 16 landing site

Lunar soils are discussed within the framework of a three-group classification scheme. Group I comprises North Ray Crater soils, group II contains light soils, and group III is made up of dark soils. It is suggested that group I soils originated from the light friable unit, one of the three units inside North Ray Crater. Group II soils were probably derived from the light matrix breccia unit; group II soils are mixtures of materials from all three units. It is concluded that soils with group III properties have been at the surface continuously for long periods. Group II soils show a record of solar wind exposure in the distant past (i.e., they have large (Ar-40/Ar-36)T ratios). Thus the regolith at the Apollo 16 site, which was observed to have marked layers of dark against light soils, contains sizeable 'pockets' or horizons at depth which are the sources of the group II soils.

Heymann, D.↗
NASA NTRS1977

Nitrogen isotopes in lunar soils as a measure of cosmic-ray exposure and regolith history

Previous studies have shown that the bulk of the nitrogen in soils has been implanted by the solar wind, that the N-15/N-14 ratio of the implanted nitrogen has apparently increased with time, and that both soils and rocks contain a nitrogen component greatly enriched in N-15, relative to natural abundance ratios, due to cosmic-ray spallation. An investigation was, therefore, conducted to test the feasibility of using spallation-produced N-15 for determining cosmic-ray exposure ages. Samples from several depths in the Apollo 15 deep drill core were analyzed. The data obtained have also been evaluated with regard to possible models for the prior history of the material now in the Apollo 15 core. In addition, analyses have been performed of several other soil samples considered for various reasons to be of particular interest, such as orange soil 74220 and its companion 74240, Apollo 16 drill core sample 60002, and the apparently peculiar fillet soil 67461. Wherever possible, analyses were carried out by step-wise heating rather than by total pyrolysis. On the basis of the results of the investigation it is concluded that nitrogen isotope ratio determinations provide a usable method for determining cosmic-ray exposures for soils.

Becker, R. H.↗
NASA NTRS1991

The origin of amorphous rims on lunar plagioclase grains: Solar wind damage or vapor condensates

A distinctive feature of micron sized plagioclase grains from mature lunar soils is a thin (20 to 100 nm) amorphous rim surrounding the grains. These rims were originally described from high voltage electron microscope observations of lunar plagioclase grains by Dran et al., who observed rims up to 100 nm thick on plagioclase grains from Apollo 11 and 12 soils. These rims are believed to be the product of solar wind damage. The amorphous rims were studied on micron sized plagioclase grains from a mature Apollo 16 soil using a JEOL 200FX transmission electron microscope equipped with an energy dispersive x ray spectrometer. It was found that the amorphous rims are compositionally distinct from the interior plagioclase and it is proposed that a major component of vapor condensates is present in the rims.

Keller, Lindsay P.↗
NASA NTRS2004

The Opportunity Rover's Athena science investigation at Meridiani Planum, Mars

The Mars Exploration Rover Opportunity has investigated the landing site in Eagle crater and the nearby plains within Meridiani Planum. The soils consist of fine-grained basaltic sand and a surface lag of hematite-rich spherules, spherule fragments, and other granules. Wind ripples are common. Underlying the thin soil layer, and exposed within small impact craters and troughs, are flat-lying sedimentary rocks. These rocks are finely laminated, are rich in sulfur, and contain abundant sulfate salts. Small-scale cross-lamination in some locations provides evidence for deposition in flowing liquid water. We interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water, followed by evaporation, exposure, and desiccation. Hematite-rich spherules are embedded in the rock and eroding from them. We interpret these spherules to be concretions formed by postdepositional diagenesis, again involving liquid water.

Mars↗
NASA NTRS1989

Long-term changes in solar wind elemental and isotopic ratios - A comparison of two lunar ilmenites of different antiquities

The solar wind components in two lunar ilmenites are examined. The noble gas and nitrogen elemental and isotopic abundances of lunar regolith breccia sample 79035, assumed to have been exposed to solar winds more than 2 Ga ago, are analyzed using stepwise oxidation and pyrolysis. This sample is compared with the data of Frick et al. (1988) for soil sample 71501, recently exposed to solar winds. It is observed that the two elements differ in terms of xenon abundance, helium and neon isotopic rates, and He/Ar elemental ratios. It is concluded that there have been isotopic and elemental abundance changes in solar wind composition over time.

Becker, Richard H.↗
NASA NTRS1977

Vibration characteristics of a large wind turbine tower on non-rigid foundations

Vibration characteristics of the Mod-OA wind turbine supported by nonrigid foundations were investigated for a range of soil rigidities. The study shows that the influence of foundation rotation on the fundamental frequency of the wind turbine is quite significant for cohesive soils or loose sand. The reduction in natural frequency can be greater than 20 percent. However, for a foundation resting on well graded, dense granular materials or bedrock, such effect is small and the foundation can be treated as a fixed base.

Yee, S. T.↗
NASA NTRS2005

Overview of the Spirit Mars Exploration Rover Mission to Gusev Crater: Landing Site to Backstay Rock in the Columbia Hills

Spirit landed on the floor of Gusev Crater and conducted initial operations on soil covered, rock-strewn cratered plains underlain by olivine-bearing basalts. Plains surface rocks are covered by wind-blown dust and show evidence for surface enrichment of soluble species as vein and void-filling materials and coatings. The surface enrichment is the result of a minor amount of transport and deposition by aqueous processes. Layered granular deposits were discovered in the Columbia Hills, with outcrops that tend to dip conformably with the topography. The granular rocks are interpreted to be volcanic ash and/or impact ejecta deposits that have been modified by aqueous fluids during and/or after emplacement. Soils consist of basaltic deposits that are weakly cohesive, relatively poorly sorted, and covered by a veneer of wind blown dust. The soils have been homogenized by wind transport over at least the several kilometer length scale traversed by the rover. Mobilization of soluble species has occurred within at least two soil deposits examined. The presence of mono-layers of coarse sand on wind-blown bedforms, together with even spacing of granule-sized surface clasts, suggest that some of the soil surfaces encountered by Spirit have not been modified by wind for some time. On the other hand, dust deposits on the surface and rover deck have changed during the course of the mission. Detection of dust devils, monitoring of the dust opacity and lower boundary layer, and coordinated experiments with orbiters provided new insights into atmosphere-surface dynamics.

Arvidson, R. E.↗
NASA NTRS1977

The regolith history of 14307

Noble gas and trace element analyses of matrix and a clast from breccia 14307 are reported. This sample was exposed to a large neutron fluence, as seen by an elevated Sm-150/Sm-149 ratio and by noble gases, particularly Xe-136 from neutron fission of U-235. Strong constraints on the exposure history result from combined consideration of Sm-150, Xe-136, and spallation noble gases. Both clast and matrix were irradiated for about 1 AE under substantial shielding beginning at least 2 AE ago, probably more than 3 AE ago. The manifestations of soil exposure seen in the matrix - solar wind gases, glass formation, etc. - thus must have been acquired in an ancient epoch. The matrix has had a longer exposure to cosmic rays than the clast, presumably during its prebrecciation history as a soil. Brecciation probably occurred more than 1 AE ago, perhaps more than 3 AE ago, but at least 0.4 AE after the formation of the matrix constituents.

Bernatowicz, T.↗
NASA NTRS1975

Light element geochemistry of the Apollo 16 site

The abundance and isotopic composition of carbon, sulfur, and nitrogen, the abundance of helium and hydrogen, and the content of metallic iron are reported for lunar surface samples from the Apollo 16 landing site at Cayley-Descartes. The light elements show marked interstation variability at the site. The abundances in soils of C, N, He, and H are apparently controlled mainly by exposure to the solar wind, through implantation or stripping processes. Carbon abundances (but not observed isotopic distributions) are compatible with a model in which equilibrium is established after 10,000-100,000 yr between solar wind input and loss by proton stripping. Sulfur abundances in soils are apparently controlled by abundances in local country rocks, but the lunar S cycle is quite complex. A metallic iron component may have originated by solar wind reduction of lunar Fe(2+).

Kerridge, J. F.↗
NASA NTRS1974

Reflectance of vegetation, soil, and water

The author has identified the following significant results. Reflectance of crop residues, that are important in reducing wind and water erosion, was more often different from bare soil in band 4 than in bands 5, 6, or 7. The plant parameters leaf area index, plant population, plant cover, and plant height explained 95.9 percent of the variation in band 7 (reflective infrared) digital counts for cotton and 78.2 percent of the variation in digital counts for the combined crops sorghum and corn; hence, measurable plant parameters explain most of the signal variation recorded for corpland. Leaf area index and plant population are both highly correlated with crop yields; since plant population can be readily measured (or possibly inferred from seeding rates), it is useful measurement for calibrating ERTS-type MSS digital data in terms of yield.

Wiegand, C. L.↗
NASA NTRS1980

A project to evaluate moisture stress in corn and soybean areas of western and southwestern Minnesota

Remote sensing techniques, particularly LANDSAT data, were used to assess soil moisture stress through crop signature in southwestern Minnesota. Related objectives were: localization of droughty, well drained, and poorly drained soils; detection of stress from hail, wind, and disease damage; and the use of remote sensing data for agricultural management. Since the amount and distribution of precipitation were adequate during the 1977 and 1978 growing seasons, no significant stress occurred. Crop conditions were very favorable. As a result, crop signatures were too uniform to reflect soilscape variations and crop condition changes. In 1979 precipitation was again adequate to excess, particularly in June and August. In some cases, poorly drained sites especially, stress conditions developed as a result of excess of water and could be identified on color infrared photographs.

Rust, R. H.↗
NASA NTRS1980

Light elements in lunar soils revisited - Carbon, nitrogen, hydrogen and helium

Based on combined data from F2-stripping and step-wise heating experiments, it is found that about 30-40% of carbon and nitrogen in submature and mature lunar soils resides in the outermost 0.1 micron of grains, presumably in the amorphous coatings that are known to be present. The remainder of carbon and nitrogen resides in composite particles such as agglutinates and microbreccias, within which C and N are distributed in a roughly uniform way. Helium shows much larger variations in its distribution between grain surfaces and interiors, with helium yield related to ilmenite content of the soil. The depth distribution of solar wind hydrogen is not readily resolvable by the stripping technique.

Becker, R. H.↗
NASA NTRS1982

Two Mars years of surface changes seen at the Viking Landing sites

An analysis of the spectrophotometric properties of the new dust deposited at the Viking Lander 1 site indicates that the new deposits are the same as the bright red material that only partially covered the site at the beginning of the mission. Certain areas of the Viking 1 site also showed an increase in contrast during the second year. The contrast increase is thought to be due to the partial removal of the recently deposited dust cover by high-velocity winds. What is more, a small soil slump occurred near the base of a boulder lying about 25 m from the lander. It is noted that whereas no obvious erosion has been detected at the Viking 2 site, periodic removal of the dust cover at this site is implied by the abundance of rocks at the site.

Guinness, E. A.↗
NASA NTRS1989

On estimating total daily evapotranspiration from remote surface temperature measurements

A method for calculating daily evapotranspiration from the daily surface energy budget using remotely sensed surface temperature and several meteorological variables is presented. Vaules of the coefficients are determined from simulations with a one-dimensional boundary layer model with vegetation cover. Model constants are obtained for vegetation and bare soil at two air temperature and wind speed levels over a range of surface roughness and wind speeds. A different means of estimating the daily evapotranspiration based on the time rate of increase of surface temperature during the morning is also considered. Both the equations using our model-derived constants and field measurements are evaluated, and a discussion of sources of error in the use of the formulation is given.

Carlson, Toby N.↗
NASA NTRS1996

Numerical Model Studies of the Martian Mesoscale Circulations

Studies concerning mesoscale topographical effects on Martian flows examined low-level jets in the near equatorial latitudes and the dynamical intensification of flow by steep terrain. Continuation of work from previous years included evaluating the dissipation of cold air mass outbreaks due to enhanced sensible heat flux, further sensitivity and scaling evaluations for generalization of the characteristics of Martian mesoscale circulation caused by horizontal sensible heat-flux gradients, and evaluations of the significance that non-uniform surface would have on enhancing the polar CO2 ice sublimation during the spring. The sensitivity of maximum and minimum atmospheric temperatures to changes in wind speed, surface albedo, and deep soil temperature was investigated.

Segal, M.↗
NASA NTRS1997

Photovoltaic Power for Mars Exploration

Mars is a challenging environment for the use of solar power. The implications of the low temperatures and low light intensity, solar spectrum modified by dust and changing with time of day and year, indirect sunlight, dust storms, deposited dust, wind, and corrosive peroxide-rich soil are discussed with respect to potential photovoltaic power systems. The power systems addressed include a solar-powered rover vehicle and a human base. High transportation costs dictate high efficiency solar cells or alternatively, a 'thin film' solar cell deposited on a lightweight plastic or thin metal foil.

Bailey, Sheila G.↗