The sampling volume of electromagnetic (EM) soil moisture sensors is of significant interest due to the diverse applications for which they are utilized. However, this volume can vary considerably based on multiple factors, including the number, spacing, and length of sensor rods, as well as the operational frequency. The sensor's volume of influence is dictated by electric field lines or ‘fringing fields’ that develop between pairs of powered electrodes. This study involved the development of an accurate sensor positioning system employed to characterize the EM sensor's electrical fringing field in 3-directional - x, y, and z space. Sensor outputs were recorded at mm increments beginning with the sensor positioned 20 mm above the air-water interface followed by incremental immersion into a water bath until the maximum sensor output was achieved. For each measurement cycle, the sensor was repositioned to test signal output approaching the air-water interface in −x, +x, −y, +y, −z, and +z orientations. The sensor sampling volume was determined based on the normalized 99% output value, which was assumed to represent the sensor position relative to an air-water interface where the sensor fringing field just begins to ‘sense’ or to become impacted by the air phase, thereby reducing the signal amplitude. Our results vary somewhat from other studies using a similar evaluation approach, leading us to conclude that EM-sensor sampling volume determination is both complex and imprecise as a result of the global sensor market's varied circuits and electrode configurations. EM soil moisture sensors evaluated in this study exhibited sampling volumes of 386 cm³ (TDR-315), 66 cm³ (TDR-310H), 398 cm³ (CS655), 45 cm³ (EC-5), 40 cm³ (HydraProbe II), 148 cm³ (WET150), and 49 cm³ (TEROS 12), which were smaller than manufacturer reported volumes.

中文翻译：

---

七个电磁土壤湿度传感器的采样量评估


电磁 (EM) 土壤湿度传感器的采样量因其用途广泛而备受关注。然而，该体积可能会因多种因素而有很大差异，包括传感器棒的数量、间距和长度以及工作频率。传感器的影响量由供电电极对之间产生的电场线或“边缘场”决定。这项研究涉及开发精确的传感器定位系统，用于表征 EM 传感器在 3 个方向（x、y 和 z 空间）中的电边缘场。从传感器定位在空气-水界面上方 20 毫米开始，以毫米增量记录传感器输出，然后逐渐浸入水浴中，直到达到最大传感器输出。对于每个测量周期，传感器被重新定位以测试在-x 、+ x 、 -y 、+ y 、 -z和+ z方向接近空气-水界面的信号输出。传感器采样体积是根据归一化的 99% 输出值确定的，假设该输出值代表传感器相对于空气-水界面的位置，其中传感器边缘场刚刚开始“感知”或受到空气相的影响，从而降低信号幅度。我们的结果与使用类似评估方法的其他研究有所不同，这使我们得出结论，由于全球传感器市场的电路和电极配置各不相同，因此电磁传感器采样量的确定既复杂又不精确。 本研究中评估的 EM 土壤湿度传感器的采样体积为 386 cm ³ (TDR-315)、66 cm ³ (TDR-310H)、398 cm ³ (CS655)、45 cm ³ (EC-5)、40 cm ³ ( HydraProbe II)、148 cm ³ (WET150) 和 49 cm ³ (TEROS 12)，小于制造商报告的体积。