Determination of Soil Water Content at Intermediate Spatial Scale Using Cosmic-Ray Neutrons: Field Application

野外水文调查的一个主要限制是缺乏跨空间尺度获取土壤含水量的方法。特别是，缺乏在中间尺度（100-1000平方）上操作的方法。M)，并且在较粗或较细的分辨率下按比例测量水文模型所需的尺度时存在相当大的不确定性。为了填补这一空白，我们开发了一种中等规模的方法，利用宇宙射线在土壤中自然产生的中子。在这个项目中，我们将应用宇宙射线中子方法来解决土壤水分测量的升级问题。为了做到这一点，我们首先需要描述探测器样土量如何取决于土壤含水量和探测器位置，以及中子信号如何在不同尺度上平均含水量的异质性。我们将通过广泛的中子通量建模和在土壤含水量可以控制的现场进行测量来实现这一目标，并通过广泛的时域反射探针网络仔细监测土壤含水量。这项工作将在图森地区的三个实地地点进行。控制洪水的实验将在图森市运营的中央阿夫拉山谷储存和恢复盆地进行。我们将利用亚利桑那大学实验农场的中心枢纽灌溉系统作为进行受控湿润试验的另一种手段。我们将在莱蒙山宇宙射线实验室的不同高度放置中子探测器并测量土壤条件，以研究土壤含水量对尺度的依赖关系。

A major limitation to field-based hydrologic investigations is a lack of means of obtaining soil water content across spatial scales. In particular, there is an absence of methods operating at the intermediate scale (100-1000 sq. m), and considerable uncertainty in scaling measurements at coarser or finer resolution to the scale required for hydrologic models. In order to fill that gap, we have developed an intermediate-scale method that utilizes neutrons produced naturally in soil by cosmic rays. In this project we will apply the cosmic-ray neutron method to the problem of upscaling soil moisture measurements. In order to do this we will first need to characterize how the detector sample volume depends on soil water content and detector positioning and how the neutron signal averages heterogeneities in water content at various scales. We will accomplish this by extensive neutron flux modeling and by performing measurements at field sites where soil water content can be controlled and carefully monitored with an extensive network of time-domain reflectometry probes.The work will be performed at three field sites in the Tucson area. Controlled flooding experiments will be performed at the Central Avra Valley Storage and Recovery basin operated by the city of Tucson. We will utilize the center-pivot irrigation system at the University of Arizona experimental farm as another means of conducting controlled wetting experiments. We will investigate the dependence of soil water content on scale by placing neutron detectors at different heights above the ground at the Mt. Lemmon Cosmic Ray Laboratory and measuring soil conditions.