Abstract
　　Soil thermal properties, including volumetric heat capacity, thermal diffusivity, and thermal conductivity, are basic physical parameters for determining the change rate of soil temperature, heat storage and transfer. The heat pulse technique, with the advantages of relative easy operation, minimal soil disturbance, and making repeated and automatic readings, has been used widely for measuring in-situ soil thermal properties. A heat pulse is emitted from a line source enclosed in a stainless heating needle and the temperature rises with time at a shorter distance from the heater are recorded for a few minutes. Soil thermal properties are then estimated from the temperature change by time data. For simplicity, the heat pulse probe is normally considered as a line source with infinitesimal probe radius and zero heat capacity when soil thermal properties are calculated. In reality, the finite properties of the probe itself, including finite heat capacity and finite probe radius, can lead to biased thermal property estimations. In this study, we compared the results of soil thermal property estimations with the PILS (pulsed-infinite-line-source) theory and ICPC (identical cylindrical perfect conductors) theory, to evaluate the influences of finite properties of the probe on soil thermal property estimations. The heat pulse probe consist of 3 needles with a diameter of 2 mm and a length of 40 mm. Heat pulse measurements were conducted on a sand soil with water content varied from air dry condition to field capacity, and soil heat capacity, thermal diffusivity, and thermal conductivity were estimated with both the PILS and ICPC methods. In addition, heat capacity estimates with the de Vries model were used to evaluate the accuracy of heat capacity measurements. The results indicated that compared with the PILS theory, the ICPC solution significantly reduced the errors in soil thermal property estimations from the temperature change-by-time curves. For water content ranging from 0.03 to 0.25 m3/m3, the PILS theory underestimated soil thermal conductivity and thermal diffusivity by 11.8% and 5.2%, respectively. Compared with the theoretical values from the de Vries model, the PILS theory and the ICPC theory overestimated soil heat capacity by 16.1% and 7.9%, respectively. Further analysis showed that that the influences of finite probe properties on thermal property estimations were most significant on dry samples, and the errors were reduced linearly with increasing soil water content. The experimental results from this study support that the theoretical analysis including finite heat capacity and finite probe radius improves the accuracies of soil thermal property estimations. The conclusions also have implications in optimizing the design of heat-pulse probes,especially for probes with relatively larger diameters.
　　Influences of finite probe property on soil thermal property estimated by heat pulse technique (PDF Download Available). Available from:
　　翻译：
　　土壤热特性,包括体积热容、热扩散系数、导热系数,是基本物理参数来确定土壤温度的变化率,热存储和传输。热脉冲技术,相对操作简单的优点,限度干扰土壤,并使重复和自动读数,已广泛用于现场测量土壤热特性。热脉冲发出一个线光源封装在一个不锈钢加热针和温度上升时间较短的距离加热器记录几分钟。土壤热特性然后从时间的温度变化数据估计。为简单起见,热脉冲探针通常被认为是与无穷小探针半径和零线源热容当土壤热力性质的计算。在现实中,有限的探测器本身的属性,包括有限热容和有限的探测半径,会导致偏见的热性能估计。在这项研究中,我们比较了土壤热特性估计的结果而得利(pulsed-infinite-line-source)理论和ICPC(相同的圆柱完美的导体)理论,评估的影响有限探测器对土壤热特性估计的性质。热脉冲探测器由3针直径2毫米和40毫米的长度。热脉冲进行了测量与含水量不同的砂质土从风干条件到田间持水量,土壤热容、热扩散系数、导热性与得利和ICPC估计方法。此外,热容估计与de Vries模型被用来评估热容测量的准确性。结果表明,与得利理论相比,ICPC的解决方案显著降低土壤热特性估计的错误change-by-time温度曲线。对水含量从0.03到0.25立方米/ m3,得利理论低估了土壤热导率和热扩散率11.8%和5.2%,分别。从de Vries模型与理论值相比,得利理论和ICPC理论高估了土壤热容16.1%和7.9%,分别。进一步分析表明,有限的探测性能的影响在热性能评估是重要的在干燥的样品,和错误减少线性增加土壤含水量。本研究的实验结果支持这一理论分析包括有限热容和有限的探测半径改善土壤热特性估计的。优化的结论也影响热脉冲探针的设计,特别是对探针与相对更大的直径。