Heated fibre optics to monitor soil moisture under successive saturation–drying cycles : An experimental approach
Bertotto, Luis Eduardo ; Reis, Alan ; Cobalchini, Érick Rúbens Oliveira ; Schwamback, Dimaghi LU
; Sousa Mota Uchôa, José Gescilam
and Wendland, Edson Cezar
(2024)
In European Journal of Soil Science
75(4).
- Abstract
In recent decades, distributed temperature sensing (DTS) has emerged as a robust technology for environmental applications, enabling high-resolution temperature measurements along fibre optic cables (FOCs). The actively heated fibre optic (AHFO) method is employed to monitor soil moisture ((Formula presented.), m3 m−3), wherein the soil temperature subsequent to the application of a heat pulse is measured by a DTS (AHFO-DTS approach). Despite significant improvements in the application of AHFO-DTS under controlled and natural conditions, the thermal behaviour of soil during multiple saturation–natural drying cycles has been insufficiently evaluated. This study aimed to address this gap by constructing an... (More)
In recent decades, distributed temperature sensing (DTS) has emerged as a robust technology for environmental applications, enabling high-resolution temperature measurements along fibre optic cables (FOCs). The actively heated fibre optic (AHFO) method is employed to monitor soil moisture ((Formula presented.), m3 m−3), wherein the soil temperature subsequent to the application of a heat pulse is measured by a DTS (AHFO-DTS approach). Despite significant improvements in the application of AHFO-DTS under controlled and natural conditions, the thermal behaviour of soil during multiple saturation–natural drying cycles has been insufficiently evaluated. This study aimed to address this gap by constructing an experimental horizontal soil profile in the laboratory for the application of the AHFO-DTS method during two successive saturation–drainage–evaporation (SDE) cycles. Three heating strategies were applied to a metallic alloy in contact with a FOC, and calibration models were used to correlate (Formula presented.) with the thermal conductivity ((Formula presented.)), cumulative temperature increase ((Formula presented.)), and maximum temperature increase ((Formula presented.)). The results indicated that during the second SDE cycle, the highest errors in (Formula presented.) estimates were observed with the low power-short heat pulse, whereas the application of the low power-long duration and high power-short duration pulses improved the accuracy of calculations. Additionally, errors in (Formula presented.) estimates escalated under wetter conditions, attributed to a shift in soil heat transfer capacity from the first to the second SDE cycle for (Formula presented.) > 0.10 m3 m−3. This behaviour was ascribed to thermal hysteresis, arising from the contact resistance of the FOC and the alloy with the surrounding soil. Furthermore, the (Formula presented.) method exhibited the least sensitivity to this effect and yielded reliable (Formula presented.) estimates, thus its adoption is recommended. Moreover, the use of the low power-long duration heating strategy is suggested as it promotes a trade-off between energy saving and accurate estimates. We concluded that assessing soil thermal response under multiple SDE cycles enhances the comprehension of the AHFO-DTS method. Overall, our findings provide insights into enhancing the applicability of this approach under field conditions, particularly following irrigation schedules and natural rainfall events.
(Less)
- author
- Bertotto, Luis Eduardo
; Reis, Alan
; Cobalchini, Érick Rúbens Oliveira
; Schwamback, Dimaghi
LU
; Sousa Mota Uchôa, José Gescilam
and Wendland, Edson Cezar
- organization
- publishing date
- 2024-07
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- distributed temperature sensing, heat pulse, soil heat transfer, soil water content
- in
- European Journal of Soil Science
- volume
- 75
- issue
- 4
- article number
- e13535
- publisher
- Wiley-Blackwell
- external identifiers
-
- scopus:85197667804
- ISSN
- 1351-0754
- DOI
- 10.1111/ejss.13535
- language
- English
- LU publication?
- yes
- id
- 5b06673f-fe6e-4bff-bbf8-8cfe1e664b07
- date added to LUP
- 2024-10-03 15:09:24
- date last changed
- 2025-04-04 14:39:11
@article{5b06673f-fe6e-4bff-bbf8-8cfe1e664b07,
abstract = {{<p>In recent decades, distributed temperature sensing (DTS) has emerged as a robust technology for environmental applications, enabling high-resolution temperature measurements along fibre optic cables (FOCs). The actively heated fibre optic (AHFO) method is employed to monitor soil moisture ((Formula presented.), m<sup>3</sup> m<sup>−3</sup>), wherein the soil temperature subsequent to the application of a heat pulse is measured by a DTS (AHFO-DTS approach). Despite significant improvements in the application of AHFO-DTS under controlled and natural conditions, the thermal behaviour of soil during multiple saturation–natural drying cycles has been insufficiently evaluated. This study aimed to address this gap by constructing an experimental horizontal soil profile in the laboratory for the application of the AHFO-DTS method during two successive saturation–drainage–evaporation (SDE) cycles. Three heating strategies were applied to a metallic alloy in contact with a FOC, and calibration models were used to correlate (Formula presented.) with the thermal conductivity ((Formula presented.)), cumulative temperature increase ((Formula presented.)), and maximum temperature increase ((Formula presented.)). The results indicated that during the second SDE cycle, the highest errors in (Formula presented.) estimates were observed with the low power-short heat pulse, whereas the application of the low power-long duration and high power-short duration pulses improved the accuracy of calculations. Additionally, errors in (Formula presented.) estimates escalated under wetter conditions, attributed to a shift in soil heat transfer capacity from the first to the second SDE cycle for (Formula presented.) > 0.10 m<sup>3</sup> m<sup>−3</sup>. This behaviour was ascribed to thermal hysteresis, arising from the contact resistance of the FOC and the alloy with the surrounding soil. Furthermore, the (Formula presented.) method exhibited the least sensitivity to this effect and yielded reliable (Formula presented.) estimates, thus its adoption is recommended. Moreover, the use of the low power-long duration heating strategy is suggested as it promotes a trade-off between energy saving and accurate estimates. We concluded that assessing soil thermal response under multiple SDE cycles enhances the comprehension of the AHFO-DTS method. Overall, our findings provide insights into enhancing the applicability of this approach under field conditions, particularly following irrigation schedules and natural rainfall events.</p>}},
author = {{Bertotto, Luis Eduardo and Reis, Alan and Cobalchini, Érick Rúbens Oliveira and Schwamback, Dimaghi and Sousa Mota Uchôa, José Gescilam and Wendland, Edson Cezar}},
issn = {{1351-0754}},
keywords = {{distributed temperature sensing; heat pulse; soil heat transfer; soil water content}},
language = {{eng}},
number = {{4}},
publisher = {{Wiley-Blackwell}},
series = {{European Journal of Soil Science}},
title = {{Heated fibre optics to monitor soil moisture under successive saturation–drying cycles : An experimental approach}},
url = {{http://dx.doi.org/10.1111/ejss.13535}},
doi = {{10.1111/ejss.13535}},
volume = {{75}},
year = {{2024}},
}