| DOI: | 10.2172/1011220
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| 报告号: | SAND2011-1101
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| 报告题名: | Radius of influence for a cosmic-ray soil moisture probe : theory and Monte Carlo simulations. |
| 作者: | David B. Frederick
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| 出版年: | 2011
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| 发表日期: | 2011-02-01
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| 总页数: | 23
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| 国家: | 美国
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| 语种: | 英语
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| 中文主题词: | 散射
; 土壤含水量
; 扩散
; 密度
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| 主题词: | SCATTERING
; SOIL MOISTURE
; DIFFUSION
; DENSITY
|
| 英文摘要: | The lateral footprint of a cosmic-ray soil moisture probe was determined using diffusion theory and neutron transport simulations. The footprint is radial and can be described by a single parameter, an e-folding length that is closely related to the slowing down length in air. In our work the slowing down length is defined as the crow-flight distance traveled by a neutron from nuclear emission as a fast neutron to detection at a lower energy threshold defined by the detector. Here the footprint is defined as the area encompassed by two e-fold distances, i.e. the area from which 86% of the recorded neutrons originate. The slowing down length is approximately 150 m at sea level for neutrons detected over a wide range of energies - from 10{sup 0} to 10{sup 5} eV. Both theory and simulations indicate that the slowing down length is inversely proportional to air density and linearly proportional to the height of the sensor above the ground for heights up to 100 m. Simulations suggest that the radius of influence for neutrons >1 eV is only slightly influenced by soil moisture content, and depends weakly on the energy sensitivity of the neutron detector. Good agreement between the theoretical slowing down length in air and the simulated slowing down length near the air/ground interface support the conclusion that the footprint is determined mainly by the neutron scattering properties of air. |
| URL: | http://www.osti.gov/scitech/servlets/purl/1011220
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| Citation statistics: |
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| 资源类型: | 研究报告
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| 标识符: | http://119.78.100.158/handle/2HF3EXSE/40324
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| Appears in Collections: | 过去全球变化的重建
影响、适应和脆弱性
科学计划与规划
气候变化与战略
全球变化的国际研究计划
气候减缓与适应
气候变化事实与影响
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| 1011220.pdf（149KB） | 研究报告 | -- | 开放获取 | | View
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| Recommended Citation: | |
David B. Frederick. Radius of influence for a cosmic-ray soil moisture probe : theory and Monte Carlo simulations.. 2011-01-01.
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