Enhancing the estimation of soil water content using a resistive heater in the dual-probe distributed temperature sensing approach

The dual-probe heat pulse (DPHP) is a well-established method for estimating soil moisture ( ) using soil thermal conductivity ( ) and volumetric heat capacity ( ). Recently, monitoring has been improved by integrating the DPHP method with distributed temperature sensing (DTS) technology. In the DPHP-DTS approach, a single fiber optic (FO) cable with embedded metallic constituents functions as a heating element, while a parallel cable serves to monitor the temperature. Despite ongoing advancements, challenges such as the difficulty in positioning heating and sensing cables and high energy requirements hinder the widespread adoption of the DPHP-DTS method. As alternative heating materials are seldom used, this study evaluated the feasibility of employing a resistive metallic alloy as the heating element in a laboratory DPHP-DTS application. Overall, higher errors were observed when assessing and at higher values (> 0.2), but using data produced more accurate estimates (with the root mean square error (RMSE) ≤ 0.06). Based on values, a low-power, long-duration heat pulse (8.07 W/m for 300 s) yielded more consistent estimates ( = 0.04) than a high-power, short-duration pulse (15.93 W/m for 180 s, with = 0.06). The findings of this study also indicated that variations in heating uniformity and electrical power fluctuations potentially affected measurement accuracy. Nevertheless, the resistive alloy proved advantageous for DPHP-DTS due to its independent power connection, ability to maintain linear positioning within the soil, and potential for energy savings, all while providing reliable estimates.