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91.
92.
Redox Processes in Groundwater Impacted by Landfill Leachate 总被引:6,自引:0,他引:6
Groundwater downgradient from Trandum municipallandfill was investigated in summer 1996, with a viewto assessing the distribution of redox-sensitivespecies. The water table at Trandum is 10–26 metersbelow the surface. Monitoring well filters have beeninstalled at depths of up to 15 m below water table,covering an area of 400 m by 200 m. Groundwaterinfluenced by the landfill seems to be confined tothis area. Pristine groundwater has a chemicalsignature indicative of calcite and pyrite weathering.Groundwater influenced by leachate from the landfillexhibits an excess of alkalinity relative to calcium,which is likely to be derived from degradation oforganic matter in the landfill. Groundwaterimmediately below and downstream of the landfillcontains elevated concentrations of Fe and Mn, largelymobilized under reducing conditions from the aquifermatrix and reflected in depleted HNO3-extractable Feand Mn in sediment samples from the same area.Groundwater samples allow the tentative identificationof redox zones based on oxidized and reduced forms ofFe, Mn, N and S. A methanogenic zone is notobserved. 相似文献
93.
New photoelectric observations of Pluto, made in 1971, 1972, and 1973, show that the amplitude of the 6-day rotational light variation is larger (about 0.22 mag) and the mean magnitude is fainter than during earlier periods of observation. The change is interpreted as due to a large obliquity of the rotational axis (probably larger than 50°). The phase coefficient of Pluto is about 0.05 mag/deg at 1° solar phase angle. 相似文献
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97.
Howard and Harvey (1970) analyzed Mt. Wilson Doppler shifts to obtain a daily measure of the Sun's differential rotation. The data were fitted to give an angular velocity of the form = a + b sin2
B + c sin4
B (B = heliographic latitude). Changes in a, b, c were found to be correlated (Howard and Harvey, 1970). Yoshimura (1972) used the anticorrelation of the b and c parameters to infer the existence of large-scale convection. Wolff (1975) used the b-c anticorrelation and a weak correlation between a and b to infer that variations of the Sun's polar and equatorial rotation rates are anticorrelated. In this paper, the anticorrelation of b and c is shown to be due to numerical coupling. 相似文献
98.
Radiative transfer corrections for accurate spectroscopic measurements of volcanic gas emissions 总被引:2,自引:1,他引:1
Christoph Kern Tim Deutschmann Leif Vogel Markus Wöhrbach Thomas Wagner Ulrich Platt 《Bulletin of Volcanology》2010,72(2):233-247
There is widespread use of passive remote sensing techniques to quantify trace gas column densities in volcanic plumes utilizing
scattered sunlight as a light source. Examples include passive DOAS, COSPEC, and the SO2 camera. In order to calculate trace gas concentrations or volcanic emission fluxes, knowledge about the optical path through
the plume is necessary. In the past, a straight photon path through the plume has always been assumed although it was known
that this is not always true. Here we present the results of model studies conducted specifically to quantify the effects
of realistic radiative transfer in and around volcanic plumes on ground-based remote sensing measurements of SO2. The results show that measurements conducted without additional information on average photon paths can be inaccurate under
certain conditions, with possible errors spanning more than an order of magnitude. Both over and underestimation of the true
column density can occur. Actual errors depend on parameters such as distance between instrument and plume, plume SO2 concentration, plume aerosol load, as well as aerosol conditions in the ambient atmosphere. As an example, a measurement
conducted with an SO2 camera is discussed, the results of which can only be correctly interpreted if realistic radiative transfer is considered.
Finally, a method is presented which for the first time allows the retrieval of actual average photon paths in spectroscopic
(i.e. DOAS) measurements of adequate resolution. By allowing for a wavelength dependent column density during the evaluation
of DOAS measurements, we show how radiative transfer effects can be corrected using information inherently available in the
measured spectra, thus greatly enhancing the accuracy of DOAS measurements of volcanic emissions. 相似文献
99.
Christoph Kern Holger Sihler Leif Vogel Claudia Rivera Martha Herrera Ulrich Platt 《Bulletin of Volcanology》2009,71(6):659-670
Active Long Path Differential Optical Absorption Spectroscopy (LP-DOAS) measurements of halogen oxides were conducted at Masaya
Volcano, in Nicaragua from April 14 to 26, 2007. The active LP-DOAS system allowed night-time halogen measurements and reduced
the ClO detection limit by an order of magnitude when compared to previous passive DOAS measurements, as wavelengths below
300 nm could be used for the DOAS retrievals. BrO was detected with an average BrO/SO2 molecular ratio of approximately 3 × 10−5 during the day. However, BrO values were below the detection limit of the instrument for all night-time measurements, a strong
indication that BrO is not directly emitted, but rather the result of photochemical formation in the plume itself according
to the autocatalytic “bromine explosion” mechanism. Despite the increased sensitivity, both ClO and OClO could not be detected.
The achieved upper limits for the X/SO2 ratios were 5 × 10−3 and 7 × 10−6, respectively. A rough calculation suggests that ClO and OClO should be present at similar abundances in volcanic plumes.
Since the DOAS technique is orders of magnitude more sensitive for OClO than for ClO, this indicates that OClO should always
be detectable in plumes in which ClO is found. However, further LP-DOAS studies are needed to conclusively clarify the role
of chlorine oxides in volcanic plumes. 相似文献
100.
Michael S. Zhdanov Masashi Endo Leif H. Cox Martin Čuma Johnathan Linfoot Chris Anderson Noel Black Alexander V. Gribenko 《Geophysical Prospecting》2014,62(3):552-572
A towed streamer electromagnetic system capable of simultaneous seismic and electromagnetic data acquisition has recently been developed and tested in the North Sea. We introduce a 3D inversion methodology for towed streamer electromagnetic data that includes a moving sensitivity domain. Our implementation is based on the 3D integral equation method for computing responses and Fréchet derivatives and uses the re‐weighted regularized conjugate gradient method for minimizing the objective functional with focusing regularization. We present two model studies relevant to hydrocarbon exploration in the North Sea. First, we demonstrate the ability of a towed electromagnetic system to detect and characterize the Harding field, a medium‐sized North Sea hydrocarbon target. We compare our 3D inversion of towed streamer electromagnetic data with 3D inversion of conventional marine controlled‐source electromagnetic data and observe few differences between the recovered models. Second, we demonstrate the ability of a towed streamer electromagnetic system to detect and characterize the Peon discovery, which is representative of an infrastructure‐led shallow gas play in the North Sea. We also present an actual case study for the 3D inversion of towed streamer electromagnetic data from the Troll field in the North Sea and demonstrate our ability to image all the Troll West Oil and Gas Provinces and the Troll East Gas Province. We conclude that 3D inversion of data from the current generation of towed streamer electromagnetic systems can adequately recover hydrocarbon‐bearing formations to depths of approximately 2 km. We note that by obviating the need for ocean‐bottom receivers, the towed streamer electromagnetic system enables electromagnetic data to be acquired over very large areas in frontier and mature basins for higher acquisition rates and relatively lower cost than conventional marine controlled‐source electromagnetic methods. 相似文献