排序方式: 共有46条查询结果,搜索用时 46 毫秒
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Jennifer L. Lewicki Deborah Bergfeld Carlo Cardellini Giovanni Chiodini Domenico Granieri Nick Varley Cynthia Werner 《Bulletin of Volcanology》2005,68(1):76-90
We present a comparative study of soil CO2 flux () measured by five groups (Groups 1–5) at the IAVCEI-CCVG Eighth Workshop on Volcanic Gases on Masaya volcano, Nicaragua. Groups 1–5 measured using the accumulation chamber method at 5-m spacing within a 900 m2 grid during a morning (AM) period. These measurements were repeated by Groups 1–3 during an afternoon (PM) period. Measured ranged from 218 to 14,719 g m−2 day−1. The variability of the five measurements made at each grid point ranged from ±5 to 167%. However, the arithmetic means of fluxes measured over the entire grid and associated total CO2 emission rate estimates varied between groups by only ±22%. All three groups that made PM measurements reported an 8–19% increase in total emissions over the AM results. Based on a comparison of measurements made during AM and PM times, we argue that this change is due in large part to natural temporal variability of gas flow, rather than to measurement error. In order to estimate the mean and associated CO2 emission rate of one data set and to map the spatial distribution, we compared six geostatistical methods: arithmetic and minimum variance unbiased estimator means of uninterpolated data, and arithmetic means of data interpolated by the multiquadric radial basis function, ordinary kriging, multi-Gaussian kriging, and sequential Gaussian simulation methods. While the total CO2 emission rates estimated using the different techniques only varied by ±4.4%, the maps showed important differences. We suggest that the sequential Gaussian simulation method yields the most realistic representation of the spatial distribution of , but a variety of geostatistical methods are appropriate to estimate the total CO2 emission rate from a study area, which is a primary goal in volcano monitoring research.Editorial responsibility: H Shinohara 相似文献
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Lehua Pan Jennifer L. Lewicki Curtis M. Oldenburg Marc L. Fischer 《Environmental Earth Sciences》2010,60(2):359-369
We use process-based modeling techniques to characterize the temporal features of natural biologically controlled surface
CO2 fluxes and the relationships between the assimilation and respiration fluxes. Based on these analyses, we develop a signal-enhancing
technique that combines a novel time-window splitting scheme, a simple median filtering, and an appropriate scaling method
to detect potential signals of leakage of CO2 from geologic carbon sequestration sites from within datasets of net near-surface CO2 flux measurements. The technique can be directly applied to measured data and does not require subjective gap filling or
data-smoothing preprocessing. Preliminary application of the new method to flux measurements from a CO2 shallow-release experiment appears promising for detecting a leakage signal relative to background variability. The leakage
index of ±2 was found to span the range of biological variability for various ecosystems as determined by observing CO2 flux data at various control sites for a number of years. 相似文献
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Jennifer L. Lewicki George E. Hilley Laura Dobeck Lee Spangler 《Environmental Earth Sciences》2010,60(2):285-297
A field facility located in Bozeman, Montana provides the opportunity to test methods to detect, locate, and quantify potential
CO2 leakage from geologic storage sites. From 9 July to 7 August 2008, 0.3 t CO2 day−1 were injected from a 100-m long, ~2.5-m deep horizontal well. Repeated measurements of soil CO2 fluxes on a grid characterized the spatio-temporal evolution of the surface leakage signal and quantified the surface leakage
rate. Infrared CO2 concentration sensors installed in the soil at 30 cm depth at 0–10 m from the well and at 4 cm above the ground at 0 and
5 m from the well recorded surface breakthrough of CO2 leakage and migration of CO2 leakage through the soil. Temporal variations in CO2 concentrations were correlated with atmospheric and soil temperature, wind speed, atmospheric pressure, rainfall, and CO2 injection rate. 相似文献
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Joshua H. Rouse Joseph A. Shaw Rick L. Lawrence Jennifer L. Lewicki Laura M. Dobeck Kevin S. Repasky Lee H. Spangler 《Environmental Earth Sciences》2010,60(2):313-323
Practical geologic CO2 sequestration will require long-term monitoring for detection of possible leakage back into the atmosphere. One potential
monitoring method is multi-spectral imaging of vegetation reflectance to detect leakage through CO2-induced plant stress. A multi-spectral imaging system was used to simultaneously record green, red, and near-infrared (NIR)
images with a real-time reflectance calibration from a 3-m tall platform, viewing vegetation near shallow subsurface CO2 releases during summers 2007 and 2008 at the Zero Emissions Research and Technology field site in Bozeman, Montana. Regression
analysis of the band reflectances and the Normalized Difference Vegetation Index with time shows significant correlation with
distance from the CO2 well, indicating the viability of this method to monitor for CO2 leakage. The 2007 data show rapid plant vigor degradation at high CO2 levels next to the well and slight nourishment at lower, but above-background CO2 concentrations. Results from the second year also show that the stress response of vegetation is strongly linked to the CO2 sink–source relationship and vegetation density. The data also show short-term effects of rain and hail. The real-time calibrated
imaging system successfully obtained data in an autonomous mode during all sky and daytime illumination conditions. 相似文献