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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Latitude measures of Jupiter in the 0.89 micron methane band

Jupiter has been photographed by the Lunar and Planetary Laboratory in the 0.89 micron methane band since October 1968. A photometric evaluation of these photographs has not yet been carried out, but a visual study of this collection and a comparison with the color records has been made. This comparison, together with diameter and latitude measures of the methane records, shows that the albedos and latitudes of most features shown in 0.89 micron vary with time and the albedos and latitudes of most features shown in 0.89 micron vary with time and that there is no simple correlation between the visual color and/or intensity of a feature and its intensity in the methane band. The latitudes of the Red Spot and South Tropical Zone have remained unchanged, while those of the Equatorial Zone, North Tropical Zone, and South Polar Hood have changed. Measures of images taken near opposition show the polar diameter to be within 0.5% of the American Ephemeris Value, but the equatorial diameter as 1.3% smaller. Measures near quadrature suggest a phase defect 3.5 times greater in value than the American Ephemeris value. The large phase defect and bright South Polar Hood contribute to the circular appearance of Jupiter in methane. Latitude variations of the North edge of the South Polar Hood support the 1964 Munch and Younkin hypothesis that this feature is composed of frozen methane.

Minton, R. B.↗
NASA NTRS1976

Laboratory band strengths of methane and their application to the atmospheres of Jupiter, Saturn, Uranus, Neptune, and Titan

This paper reports laboratory studies of the visible spectrum of methane at column densities between 0.4 and 5 km-am and confirms the identification of bands at 4410, 4590, 4860, 5090, 5430, 5760, and 5970 A as caused by methane. Detailed equivalent-width measurements at 15 different pressure path lengths are employed to determine curves of growth and band strengths for the bands at 4410, 4860, 5430, and 5760 A. Using the curve-of-growth measurements in the reduction of planetary observations, the methane abundances in the atmospheres of Jupiter and Saturn are found to be between a factor of 3 and 4 larger than previously accepted values based on the analysis of the 3 nu(3) band at 1.1 microns, while the amount on Titan is significantly less than that obtained from an analysis of the same band with the assumption of a pure methane atmosphere. The present results, when combined with the band analysis, suggest a surface pressure on Titan of at least 0.4 atm. Extrapolation of these laboratory data to observations of Uranus and Neptune lead to single-air-mass column densities of 5.8 and 7.6 km-am of methane, respectively.

Lutz, B. L.↗
NASA NTRS1980

Impact of a global warming on biospheric sources of methane and its climatic consequences

Most of atmospheric methane originates by bacterial processes in anaerobic environments within the soil which are found to become more productive with increases in ambient temperature. A warming of climate, due to increasing levels of industrial gases resulting from fossil fuel burning, is thus likely to increase methane abundance within the atmosphere. This may lead to further heating of the atmosphere, since both methane and ozone (which is generated in the troposphere from reactions of methane) have greenhouse effects. This feedback mechanism has been explored with the use of a coupled climate-chemical model of the troposphere, by the calculation of the impact of the predicted global warming due to increased emissions of carbon dioxide and other industrial gases on the biospheric sources of methane.

Hameed, S.↗
NASA NTRS1981

Sources of atmospheric methane - Measurements in rice paddies and a discussion

Field measurements of methane fluxes from rice paddies, fresh water lakes, and saltwater marshes have been made to infer estimates of the size of these sources of atmospheric methane. The rice-paddy measurements, the first of their kind, show that the principal means of methane escape is through the plants themselves as opposed to transport across the water-air interface via bubbles or molecular diffusion. Nitrogen-fertilized plants release much more methane than unfertilized plants but even these measured rates are only one fourth as large as those inferred earlier by Koyama (1963, 1964) and on which all global extrapolations have been based to date. Measured methane fluxes from lakes and marshes are also compared to similar earlier data and it is found that extant data and flux-measurement methods are insufficient for reliable global extrapolations.

Cicerone, R. J.↗
NASA NTRS1982

Methane flux in the Great Dismal Swamp

The paper reports measurements made over a 17-month period of the methane flux in the Great Dismal Swamp of Virginia in light of the potential implications of variations in atmospheric methane concentrations. Gas flux measurements were made by a technique combining a gas filter correlation IR absorption analyzer with improved sampling chambers that enclose a soil area under conditions ranging from totally flooded soils to dry soils resulting from drought conditions. Methane emissions are found to range from 0.0013 g CH4/sq m per day to 0.019 g CH4/sq m per day, depending on temperature and season, when the soil is in a waterlogged state. During drought conditions, the peat soils in the swamp were a sink for atmospheric methane, with fluxes from less than 0.001 to 0.005 g CH4/sq m per day and decreasing with decreasing temperature. Results illustrate the potential complexity of the processes which regulate the net flux of methane between wetland soils and the atmosphere.

Harriss, R. C.↗
NASA NTRS1983

Sources, sinks, and seasonal cycles of atmospheric methane

It is shown that a lifetime of approximately 8 years is most consistent with the observed latitudinal variation of atmospheric methane, requiring the current global emissions of methane to be around 550 teragrams per year. The repeating pattern of a rapid rise of CH4 concentrations in the fall in the Northern Hemisphere indicates a large fall source at latitudes above 30 deg N. The remaining observed seasonal variations are seen as consistent with the seasonal cycle of OH, which removes methane from the atmosphere. An extensive set of self-consistent measurements of methane is reported and analyzed, revealing that methane has increased during the past 3-4 years at rates of 1-1.9 percent per year all over the world at sites ranging from inside the Arctic Circle to the South Pole. The observational results are used in estimating the sources, sinks, and seasonal cycles of CH4 and the effects of human activities on its atmospheric abundance.

Khalil, M. A. K.↗
NASA NTRS1984

Methane on Triton - Physical state and distribution

Infrared spectrophotometric measurements of Neptune's satellite Triton obtained between 1980 and 1982 in the spectral range 0.8-2.5 microns show six individual absorption bands attributable to methane. An additional band in the Triton data is not methane. The Triton spectral data conform more closely to a laboratory spectrum of frozen methane than to a synthetic spectrum of methane gas computed for conditions of low temperature expected at the satellite. Additionally, the strength of the bands vary with Triton's orbital position. The data thus suggest that methane in the ice phase is mostly responsible for the bands in Triton's spectrum, and that the ice is distributed nonuniformly around the satellite's surface.

Cruikshank, D. P.↗
NASA NTRS1985

Methane flux from coastal salt marshes

It is thought that biological methanogenesis in natural and agricultural wetlands and enteric fermentation in animals are the dominant sources of global tropospheric methane. It is pointed out that the anaerobic soils and sediments, where methanogenesis occurs, predominate in coastal marine wetlands. Coastal marine wetlands are generally believed to be approximately equal in area to freshwater wetlands. For this reason, coastal marine wetlands may be a globally significant source of atmospheric methane. The present investigation is concerned with the results of a study of direct measurements of methane fluxes to the atmosphere from salt marsh soils and of indirect determinations of fluxes from tidal creek waters. In addition, measurements of methane distributions in coastal marine wetland sediments and water are presented. The results of the investigation suggest that marine wetlands provide only a minor contribution to atmospheric methane on a global scale.

Bartlett, K. B.↗
NASA NTRS1985

Determination of methane in ambient air by multiplex gas chromatography

A multiplex gas chromatographic technique for the determination of methane in ambient air over extended periods is reported. A modest gas chromatograph which uses air as the carrier gas was modified by adding a silver oxide sample modulator for multiplex operation. The modulator selectively catalyzes the decomposition of methane in air. The resulting analytical system requires no consumables beyond power. A profile of the methane concentration in this laboratory was obtained for an 8-day period. During this period, methane concentration varied with an approximately daily period from a low of 1.53 + or - 0.60 ppm to a high of 4.63 + or - 0.59 ppm over the entire 8 days. Some of the measured concentrations are higher than those reported elsewhere indicating the presence of some local source or sources for methane. This work has demonstrated the utility of a relatively simple multiplex gas chromatograph for the analysis of environmental samples. The technique should be applicable to other trace components in air through use of other selective modulators.

Valentin, J. R.↗
NASA NTRS1986

Emission of methane and other trace gases from the Amazon Varzea

Researchers measured the distributions and fluxes of methane and other trace gases from the various Amazon floodplain environments. These were determined during both a large scale, quasi-synoptic survey along a 2000 km reach of the Amazon river and an intensive local study (by J. Melack, R. Harriss et al.) covering a six-week period. The environments studied included the major rivers, connecting channels (paranas), floating macrophyte beds, flooded forests, open lakes and recently wetted soils. The results are summarized. Measured rates of methane emission averaged about 300 mg m-2 d-1, but with considerable variance, and were comparable to or higher than previously reported emissions from similar temperature zone environments. In general, areas covered by floating macrophytes showed the highest emissions. Individual hotspots had among the highest rates ever observed, over 10 g m-2 d-1. The high methane emissions appear to result because about 50% of the organic matter fixed on the floodplain (either terrestrial or aquatic) that is oxidized in the water is decomposed anaerobically via methanogensis. Measured fluxes of methane to the atmosphere appear to be significantly correlated with surface water dissolved methane concentrations.

Richey, Jeffrey E.↗
NASA NTRS1986

Seasonal variations in the stable carbon isotopic signature of biogenic methane in a coastal sediment

Systematic seasonal variations in the stable carbon isotopic signature of methane gas occur in the anoxic sediments of Cape Lookout Bight, a lagoonal basin on North Carolina's Outer Banks. Values for the carbon isotope ratio of methane range from -57.3 per mil during summer to -68.5 per mil during winter in gas bubbles with an average methane content of 95 percent. The variations are hypothesized to result from changes in the pathways of microbial methane production and cycling of key substrates including acetate and hydrogen. The use of stable isotopic signatures to investigate the global methane cycle through mass balance calculations, involving various sediment and soil biogenic sources, appears to require seasonally averaged data from individual sites.

Martens, C. S.↗
NASA NTRS1990

Methane fluxes in wetland and forest soils, beaver ponds, and low-order streams of a temperate forest ecosystem

This study was conducted to determine whether temperate wetlands and forests play important roles in the global balances of atmospheric methane. Flux measurements for methane in several different wetland, forest, and open-water (e.g., beaver pond and low-order stream) sites were determined using collection chambers placed over the soil- or water-air interface. All of the sites were located in the Appalachian Mountain region of West Virginia and western Maryland. Between June 1987 and April 1989 the wetland sites acted as small sources of atmospheric methane, with emission rates for methane usually lower than 200 mg CH4/sq m per day; consumption of atmospheric methane in the wetland soils was observed frequently.

Yavitt, J. B.↗
NASA NTRS1992

Modelling global methane emissions from livestock: Biological and nutritional controls

The available observations of methane production from the literature have been compiled into a ruminant methane data base. This data base includes 400 treatment mean observations of methane losses from cattle and sheep, and minor numbers of measurements from other species. Methane loss varied from 2.0 to 11.6 percent of dietary gross energy. Measurements included describe the many different weights and physiological states of the animals fed and diets ranging from all forage to all concentrate diets or mixtures. An auxiliary spreadsheet lists approximately 1000 individual animal observations. Many important concepts have emerged from our query and analysis of this data set. The majority of the world's cattle, sheep, and goats under normal husbandry circumstances likely produce methane very close to 6 percent of their daily diets gross energy (2 percent of the diet by weight). Although individual animals or losses from specific dietary research circumstances can vary considerably, the average for the vast majority of groups of ruminant livestock are likely to fall between 5.5 to 6.5 percent. We must caution, however, that little experimental data is available for two-thirds of the world's ruminants in developing countries. Available evidence suggests similar percentage of emissions, but this supposition needs confirmation. More importantly, data is skimpy or unavailable to describe diet consumption, animal weight, and class distribution.

Johnson, Donald E.↗
NASA NTRS1994

Rice cultivation and methane emission: Documentation of distributed geographic data sets

High-resolution global data bases on the geographic and seasonal distribution of rice cultivation and associated methane emission, compiled by Matthews et al., were archived for public use. In addition to the primary data sets identifying location, seasonality, and methane emission from rice cultivation, a series of supporting data sets is included, allowing users not only to replicate the work of Matthews et al. but to investigate alternative cultivation and emission scenarios. The suite of databases provided, at 1 latitude by 1 longitude resolution for the globe, includes (1) locations of rice cultivation, (2) monthly arrays of actively growing rice areas, (3) countries and political subdivisions, and (4) monthly arrays of methane emission from rice cultivation. Ancillary data include (1) a listing, by country, of harvested rice areas and seasonal distribution of crop cycles and (2) country names and codes. Summary tables of zonal/monthly distributions of actively growing rice areas and of methane emissions are presented. Users should consult original publications for complete discussion of the data bases. This short paper is designed only to document formats of the distributed information and briefly describe the contents of the data sets and their initial application to evaluating the role of rice cultivation in the methane budget.

Matthews, Elaine↗
NASA NTRS1994

Clouds, hazes, and the stratospheric methane abundance in Neptune

Analysis of high-spatial-resolution (approximately 0.8 arcsec) methane band and continuum imagery of Neptune's relatively homogeneous Equatorial Region yields significant constraints on (1) the stratospheric gaseous methane mixing ratio (f(sub CH4, S)), (2) the column abundances and optical properties of stratospheric and tropospheric hydrocarbon hazes, and (3) the wavelength-dependent single-scattering albedo of the 3-bar opaque cloud. From the center-to-limb behavior of the 7270-A and 8900-A CH4 bands, the stratospheric methane mixing ratios is limited to f(sub CH4, S) less than 1.7 x 10(exp -3), with a nominal value of f(sub CH4, S) = 3.5 x 10(exp -4), one to two orders of magnitude less than pre-Voyager estimates, but in agreement with a number of recent ultraviolet and thermal infrared measurements, and largely in agreement with the tropopause mixing ratio implied by Voyager temperature measurements. Upper limits to the stratospheric haze mass column abundance and 6190-A and 8900-A haze opacities are 0.61 micrograms/sq cm and 0.075 and 0.042, respectively, with nominal values of 0.20 micrograms/sq cm and 0.025 and 0.014 for the 0.2 micrometers radius particles preferred by the recent Voyager PPS analysis of Pryor et al. (1992). The tropospheric CH4 haze opacities are comparable to that found in the stratosphere, i.e., upper limits of 0.104 and 0.065 at 6190 A and 8900 A, respectively, with nominal values of 0.085 and 0.058. This indicates a column abundance less than 11.0 micrograms/sq cm, corresponding to the methane gas content within a well-mixed 3% methane tropospheric layer only 0.1 cm thick near the 1.5-bar CH4 condensation level. Conservative scattering is ruled out for the opaque cloud near 3 bars marking the bottom of the visible atmosphere. Specifically, we find cloud single-scattering albedos of 0.915 +/- 0.006 at 6340 A, 0.775 +/- 0.012 at 7490 A, and 0.803 +/- 0.010 at 8260 A. Global models utilizing a complete global spectrum confirm the red-absorbing character of the 3-bar cloud. The global-mean model has approximately 7.7 times greater stratospheric aerosol content than the Equatorial Region. An analysis of stratospheric haze precipitation rates indicates a steady-state haze production rate of 0.185-1.5 x 10(exp -14) g/sq cm/s, in agreement with recent theoretical photochemical estimates. Finally, reanalysis of the Voyager PPS 7500-A phase angle data utilizing the f(sub CH4, S) value derived here confirms the Pryor et al. result of a tropospheric CH4 haze opacity of a few tenths in the 22-30 degs S latitude region, several times that of the Equatorial Region or of the globe. The factor-of-10 reduction in f(sub CH4, S) below that assumed by Pryor et al. implies decreased gas absorption and consequently a decrease in the forward-scattering component of tropospheric aerosols.

Baines, Kevin H.↗
NASA NTRS1994

Optical constants of liquid and solid methane

The optical constants n(sub r) + in(sub i) of liquid methane and phase 1 solid methane were determined over the entire spectral range by the use of various data sources published in the literature. Kramers-Kronig analyses were performed on the absorption spectra of liquid methane at the boiling point (111 K) and the melting point (90 K) and on the absorption spectra of phase 1 solid methane at the melting point and at 30 K. Measurements of the static dielectric constant at these temperatures and refractive indices determined over limited spectral ranges were used as constraints in the analyses. Applications of methane optical properties to studies of outer solar system bodies are described.

Martonchik, John V.↗
NASA NTRS1997

An Ecosystem Simulation Model for Methane Production and Emission from Wetlands

Previous experimental studies suggest that methane emission from wetland is influenced by multiple interactive pathways of gas production and transport through soil and sediment layers to the atmosphere. The objective of this study is to evaluate a new simulation model of methane production and emission in wetland soils that was developed initially to help identify key processes that regulate methanogenesis and net flux of CH4 to the air, but which is designed ultimately for regional simulation using remotely sensed inputs for land cover characteristics. The foundation for these computer simulations is based on a well-documented model (CASA) of ecosystem production and carbon cycling in the terrestrial blaspheme. Modifications to represent flooded wetland soils and anaerobic decomposition include three new sub-models for: (1) layered soil temperature and water table depth (WTD) as a function of daily climate drivers, (2) CH4 production within the anoxic soil layer as a function of WTD and CO2 production under poorly drained conditions, and (3) CH4 gaseous transport pathways (molecular diffusion, ebullition, and plant vascular transport) as a function of WTD and ecosystem type. The model was applied and tested using climate and ecological data to characterize tundra wetland sites near Fairbanks, Alaska studied previously by Whalen and Reeburgh. Comparison of model predictions to measurements of soil temperature and thaw depth, water-table depth, and CH4 emissions over a two year period suggest that inter-site differences in soil physical conditions and methane fluxes could be reproduced accurately for selected periods. Day-to-day comparison of predicted emissions to measured CH4 flux rates reveals good agreement during the early part of the thaw season, but the model tends to underestimate production of CH4 during the months of July and August in both test years. Important seasonal effects, including that of falling WTD during these periods, are apparently overlooked in the model formulation. Nevertheless, reasonably close agreement was achieved between the model's mean daily and seasonal estimates of CH4 flux and observed emission rates for northern wetland ecosystems. Several features of the model are identified as crucial to more accurate prediction of wetland methane emission, including the capacity to incorporate influences of localized topographic and hydrologic features on site-specific soil temperature and WTD dynamics, and mechanistic simulation of methane emission transport pathways from within the soil profile.

Potter, C. S.↗
NASA NTRS2005

Thinking Like a Wildcatter: Prospecting for Methane in Arabia Terra, Mars

Methane has been detected in the martian atmosphere at a concentration of approximately 10 ppb. The lifetime of such methane against decomposition by solar radiation is approximately 300 years, strongly suggesting that methane is currently being released to the atmosphere. By analogy to Earth, possible methane sources on Mars include active volcanism, hot springs, frozen methane clathrates, thermally-matured sedimentary organic matter, and extant microbial metabolism. The discovery of any one of these sources would revolutionize our understanding of Mars.

Allen, C. C.↗