Radius of influence for a cosmic-ray soil moisture probe : theory and Monte Carlo simulations.

doi:10.2172/1011220

GSTDTAP > 地球科学

DOI	10.2172/1011220
报告编号	SAND2011-1101
来源ID	OSTI ID: 1011220
	Radius of influence for a cosmic-ray soil moisture probe : theory and Monte Carlo simulations.
	David B. Frederick
	2011-02-01
出版年	2011
页数	23
语种	英语
国家	美国
领域	地球科学
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.
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来源平台	US Department of Energy (DOE)
引用统计
文献类型	科技报告
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/5437
专题	地球科学
推荐引用方式 GB/T 7714	David B. Frederick. Radius of influence for a cosmic-ray soil moisture probe : theory and Monte Carlo simulations.,2011.