Comparison of Heating Strategies on Soil Water Measurement Using Actively Heated Fiber Optics on Contrasting Textured Soils

Abstract

The actively heated fiber optics (AHFO) technique has the potential to measure soil water at high spatial and temporal resolutions, and thus it can bridge the measurement gap from point to large scales. However, the availability of power might restrict its use, since high power is required to heat long fiber optic cables under field conditions; this can be a challenge for long-term soil water monitoring under field conditions. This study investigated the performance of different heating strategies (power intensity and heating duration) on soil water measurement by the AHFO technique on three different textured soils. Different heating strategies: high power–short pulses (20 Wm−1–3 min), low power–short pulses (10 Wm−1–3 min, 5 Wm−1–3 min, 2.5 Wm−1–3 min) and low power–long pulses (10 Wm−1–5 min, 5 Wm−1–10 min, 2.5 Wm−1–15 min) were tested using laboratory soil columns. The study compared the sensitivity of the thermal response, NTcum to volumetric water content (VWC) and the predictive error of different heating strategies and soils. Results of this study showed that the sensitivity of NTcum increased and the predictive error decreased with increasing power intensity, irrespective of the soil type. Low power–short heat pulses such as 5 Wm−1–3 min and 2.5 Wm−1–3 min produced high predictive errors, RMSE of 5–6% and 6–7%, respectively. However, extending the heating duration was effective in reducing the error for both 10 and 5 Wm−1 power intensities, but not for the 2.5 Wm−1. The improvement was particularly noticeable in 5 Wm−1 –10 min; it reduced the RMSE by 1.5% (sand and clay loam) and 2.73% (sandy loam). Overall, the results of this study suggested that extending the heating duration of 10 and 5 Wm−1 power intensities can improve the sensitivity of the thermal response and predictive accuracy of the estimated soil water content (SWC). The results are particularly important for field applications of the AHFO technique, which can be limited by the availability of high power, which restricts the use of 20 Wm−1. For example, 5 Wm−1–10 min improved the predictive accuracy to 3–4%, which has the potential to be used for validating soil water estimations at satellite footprint scales. However, the effects of diurnal temperature variations should also be considered, particularly when using low power intensity such as 5 Wm−1 in surface soils under field conditions.

Challenges and advances in measuring sap flow in agriculture and agroforestry: A review with focus on nuclear magnetic resonance

“…The most critical components of the SPAC are plant water potential, soil moisture content, plant uptake, evapotranspiration, and dynamics of xylem transport (Vicente et al, 2003;Fayer and Gee, 2004;Vidana Gamage et al, 2021). In plants, sap flow in the stem is used as an indicator of transpiration and water usage.…”

“…The study of this movement of water from soil to plant and to atmosphere is referred as soil-plant-atmosphere continuum (SPAC), which has become a dominant framework for understanding plant water movement ( Deng et al., 2017 ). The most critical components of the SPAC are plant water potential, soil moisture content, plant uptake, evapotranspiration, and dynamics of xylem transport ( Vicente et al., 2003 ; Fayer and Gee, 2004 ; Vidana Gamage et al., 2021 ). In plants, sap flow in the stem is used as an indicator of transpiration and water usage.…”

An Individual Household-Based Heating Metering and Charging Management System for Central Heating in Community Residential Buildings

“…The developed European and American countries generally have sound heating systems and hot water charging standards built based on heat consumption [4][5][6]. In China, after going through a few stages of initial exploration, technology upgrade, pilot demonstration, international cooperation, and gradual promotion, the adopted heating metering and charging management strategies have achieved obvious energy-saving effect, the heat sharing has certain social fairness, but for the related techniques and standards, there're still much room for improvement [7][8][9][10].…”

Investigação da umidade do solo por meio da combinação entre o aquecimento de uma liga ferrítica (Fe-Cr-Al) e a medição distribuída de temperatura (DTS)

“…Por causa disso, recentemente, algumas pesquisas buscaram avaliar diferentes estratégias de aquecimento. Em comparação a aplicações de alta potência, ótimos resultados foram encontrados especialmente utilizando pulsos de calor de baixa potência e longa duração (i.e., 5 W.m -1 e 600 s) (GAMAGE et al, 2021). O teor de umidade foi monitorado em cada tubo experimental com sensores pontuais.…”

“…Para um mesmo solo, quanto maior é 𝜃, maiores são 𝐶 e 𝜆. Uma vez que a água funciona como uma ponte que une as partículas sólidas do solo, ela permite que o calor seja transportado para longe da fonte aquecedora mais rapidamente, além de fornecer maior potencial de armazenamento de calor ao meio poroso, o que dificulta o seu aquecimento (SOURBEER; LOHEIDE II, 2015). Assim, mudanças de temperatura são mais difíceis de serem alcançadas para maiores valores de 𝜃. Dessa forma, por meio da aplicação dos métodos HP e AHFO, é possível estabelecer uma relação inversamente proporcional entre 𝜃 e o aumento de temperatura observado (GAMAGE et al, 2021;LAGOS et al, 2020).…”