Root zone soil moisture (RZSM) is important in sustaining terrestrial ecosystems and water cycling. However, noninvasive mapping of RZSM remains challenging in the field, especially its spatial variability at local scales. We propose a novel method of applying ground‐penetrating radar (GPR) for noninvasive determination of RZSM. First, this method identified coarse root reflections in GPR images to obtain the reflected wave velocity and soil water storage at various locations. Then, the horizontal distributions of soil water storage to different depths were reconstructed using the inverse distance weighted interpolation. The difference in soil water storage between two depths was converted into 2D RZSM distribution for a specific depth interval. Finally, 2D RZSM distributions from a range of depths were combined to produce a 3D visualization of RZSM. The proposed method was validated in two field plots (30 m by 30 m) in shrublands. The comparisons with 2D RZSM distributions from soil cores sampled at 0.2‐m depth intervals suggested a reasonable correspondence in both spatial patterns and absolute values, with the average root‐mean‐square error less than 0.017 m·m and correlation coefficients ranging from 0.502 to 0.798 in both plots. Furthermore, 3D visualizations of RZSM were generated based on GPR estimates to demonstrate the spatial variability of soil moisture at the study scale. The proposed method enhances noninvasive characterization of soil moisture down to the root zone, which contributes to a better understanding of the local‐scale variability of soil moisture in the subsoil as well as the ecohydrological processes in the soil‐plant‐atmosphere continuum.

中文翻译：

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通过探地雷达探测粗根对根区土壤水分进行非侵入式 2D 和 3D 制图

根区土壤水分 (RZSM) 在维持陆地生态系统和水循环方面很重要。然而，RZSM 的无创制图在该领域仍然具有挑战性，尤其是其在局部尺度上的空间变异性。我们提出了一种应用探地雷达 (GPR) 无创确定 RZSM 的新方法。首先，该方法识别 GPR 图像中的粗根反射，以获得不同位置的反射波速度和土壤蓄水量。然后，利用逆距离加权插值法重建了不同深度土壤蓄水量的水平分布。将两个深度之间土壤储水量的差异转换为特定深度间隔的二维 RZSM 分布。最后，来自一系列深度的 2D RZSM 分布被组合以产生 RZSM 的 3D 可视化。所提出的方法在灌木地的两个田间地块（30 m x 30 m）中得到了验证。与以 0.2 米深度间隔采样的土壤核心的二维 RZSM 分布的比较表明，空间模式和绝对值均具有合理的对应关系，平均均方根误差小于 0.017 m·m，相关系数范围为 0.502 至两个图中均为 0.798。此外，RZSM 的 3D 可视化是基于 GPR 估计生成的，以证明研究范围内土壤水分的空间变异性。所提出的方法增强了土壤水分的非侵入性表征，直至根区，