Soil profile water content determination: Sensor accuracy, axial response, calibration, temperature dependence, and precision
Soil profile water content determination: Sensor accuracy, axial response, calibration, temperature dependence, and precision
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DOI：
10.2136/vzj2005.0149
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发表时间：
2006-08-01
影响因子：
2.8
通讯作者：
Howell, Terry A.
中科院分区：
文献类型：
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作者：
Evett, Steven R.;Tolk, Judy A.;Howell, Terry A.
尽管中子水分计 (NMM) 很好地满足了准确测定土壤水分含量的需求，但不断增加的监管负担（包括要求 NMM 无人看管）限制了该方法的实用性。较新的方法响应土壤电磁（EM）特性，通常允许数据记录和无人值守操作，但精度、准确度和灵敏度不确定。在三种土壤的实验室柱中，我们将 Sentek EnviroSCAN 和 diviner 2000 电容设备、Delta-T PR1/6 Profiler 电容探头、Trime T3 管探头、所有 EM 方法与 NMM 和传统时域反射计（TDR，也是一种 EM 方法）进行了比较。除传统 TDR 外，所有 TDR 均可用于接入管。在润湿至饱和之前、期间和之后对总粘土含量从 17% 到 48% 的三种土壤进行三次重新填充柱进行测量。每根柱子都连续称重，并且每 30 分钟用热电偶测定一次温度。除 NMM 外，所有设备都对温度敏感，而传统 TDR 是 EM 设备中最不敏感的（Trime 和 Delta-T 设备的灵敏度为 0.01 m(3) m(-3)）。设备的准确性通过质量平衡确定的柱平均水含量与使用工厂校准的设备确定的柱平均水含量之间的均方根差 (RMSD) 来判断。RMSD 度量值越小，表明工厂校准越准确。Delta-T 系统的精度最低。准确，饱和时的 RMSD 为 1.299 m(3) m(-3)，Diviner、EnviroSCAN、NMM 和 Trime 设备的 RMSD 值均 > 0.05 m(3) m(-3)，而 TDR 的 RMSD < 0.03 m(3) m(-3) 本研究中确定的土壤特定校准导致回归值（校准精度指标）的 RMSE 0.010 至 0.058 m(3) m(-3) 的所有设备都需要针对不同的土壤层进行单独校准。在 EM 设备中，只有 Delta-T PR1/6 的轴向灵敏度明显大于传感器的轴向高度，这表明测量体积通常较小，并表明这些系统可能容易受到土壤含水量小范围变化（小于含水量的代表性元素体积）和接近接入管引起的土壤扰动的影响。在安装过程中。
Although the neutron moisture meter (NMM) has served the need for accurate soil water content determinations well, increasing regulatory burdens, including the requirement that the NMM not be left unattended, limit the usefulness of the method. Newer methods, which respond to soil electromagnetic (EM) properties, typically allow data logging and unattended operation, but with uncertain precision, accuracy, and volume of sensitivity. In laboratory columns of three soils, we compared the Sentek EnviroSCAN and Diviner 2000 capacitance devices, the Delta-T PR1/6 Profiler capacitance probe, the Trime T3 tube-probe, all EM methods, with the NMM and conventional time domain reflectometry (TDR, also an EM method). All but conventional TDR can be used in access tubes. Measurements were made before, during, and after wetting to saturation in triplicate repacked columns of three soils ranging in total clay content from 17 to 48%. Each column was weighed continuously, and thermocouple determinations of temperature were made every 30 min throughout. All of the devices were sensitive to temperature except for the NMM, with conventional TDR being the least sensitive of the EM devices ( sensitivity 0.01 m(3) m(-3) for the Trime and Delta-T devices. Accuracy of the devices was judged by the root mean squared difference (RMSD) between column mean water contents determined by mass balance and those determined by the devices using factory calibrations. Smaller values of the RMSD metric indicated more accurate factory calibration. The Delta-T system was least accurate, with an RMSD of 1.299 m(3) m(-3) at saturation. At saturation, the Diviner, EnviroSCAN, NMM, and Trime devices all exhibited RMSD values > 0.05 m(3) m(-3), while TDR exhibited RMSD < 0.03 m(3) m(-3). Soil-specific calibrations determined in this study resulted in RMSE of regression values (an indicator of calibration accuracy) ranging from 0.010 to 0.058 m(3) m(-3). All of the devices would require separate calibrations for different soil horizons. Of the EM devices, only the Delta-T PR1/6 exhibited axial sensitivity appreciably larger than the axial height of the sensor, indicating small measurement volumes generally, and suggesting that these systems may be susceptible to small-scale variations in soil water content (at scales smaller than the representative elemental volume for water content) and to soil disturbance close to the access tube caused during installation.