Assessing vertical soil moisture dynamics using multi-frequency GPR common-midpoint soundings
Assessing vertical soil moisture dynamics using multi-frequency GPR common-midpoint soundings
复制标题
DOI：
10.1016/j.jhydrol.2012.02.041
复制
发表时间：
2012-05
影响因子：
6.4
通讯作者：
C. Steelman;A. Endres
中科院分区：
文献类型：
--
作者：
C. Steelman;A. Endres
土壤水分测量技术对于包气带水文学家来说是至关重要的。地表水文地球物理方法，如探地雷达(GPR)，有能力提供各种深度尺度上的田间尺度土壤水分信息。利用多频率(即225 MHz、450 MHz、900 MHz)探地雷达共中点(CMP)测深对三个不同地点的土壤水分状况进行了完整的年周期监测。我们研究了将正常时差(NMO)速度分析应用于CMP数据，以监测中纬度气候中高度动态的垂直土壤水分条件，该气候包括不同程度的湿/干和冻结/融化循环和垂直速度梯度。动校速度分析用于在固定位置建立每1-4周采集一次的层速度-深度模型。这些时移模型被组合在一起来构建时间层速度场，并利用适当的岩石物理关系将其转换为土壤水分含量。利用这些水分场，我们能够表征浅层包气带土壤水分的垂直分布和动态。虽然多个天线频率的使用提供了不同的调查深度和垂直分辨率，但使用900 MHz高频天线获得了土壤水分条件的最佳表征。将直接地波和动校正波速度数据整合在一起，使我们能够在季节性湿、干和冻结循环期间更好地精炼浅层土壤水分剖面和潜在的包气带条件。这项研究展示了探地雷达描述垂直水分动态的能力，并强调了沿空气-土壤界面收集高分辨率数据的重要性，以解析从表层到更深的包气带条件下的水分剖面。
Soil moisture measurement techniques are of utmost importance to vadose zone hydrologists. Surface hydrogeophysical methods, such as ground-penetrating radar (GPR), have the capacity to provide field-scale soil moisture information across a range of depth scales. This paper presents an extensive field study using multi-frequency (i.e., 225MHz, 450MHz, 900MHz) GPR common-midpoint (CMP) soundings to monitor a complete annual cycle of soil moisture conditions at three distinct sites. We examine the use of normal-moveout (NMO) velocity analysis applied to CMP data for monitoring highly dynamic vertical soil moisture conditions in a mid-latitude climate consisting of wetting/drying and freeze/thaw cycles with varying degrees of magnitude and vertical velocity gradient. NMO velocity analysis is used to construct interval-velocity-depth models at a fixed location collected every 1–4weeks. These time-lapse models are combined to construct temporal interval-velocity fields, which are converted into soil moisture content using an appropriate petrophysical relationship. Using these moisture fields, we were able to characterize the vertical distribution and dynamics of soil moisture in the shallow vadose zone. Although the use of multiple antenna frequencies provided varying investigation depths and vertical resolving capabilities, optimal characterization of soil moisture conditions was obtained with high-frequency 900MHz antennas. The integration of direct ground wave and NMO velocity data from a single CMP sounding allowed us to better refine the shallow soil moisture profile and underlying vadose zone conditions during seasonal wetting, drying and freezing cycles. This study demonstrates the capacity of GPR to characterize vertical moisture dynamics, and highlights the importance of collecting high-resolution data along the air–soil interface to resolve the water content profile from the surface down to the deeper vadose zone conditions.