Active DTS for spatio-temporal soil moisture monitoring Curioni G. 1 , Krause S. 1 , Ciocca F. 2 1 School of Geography, Earth & Environmental Sciences, University of Birmingham, Birmingham, UK 2 Silixa Ltd., London, UK Contact Author: Giulio Curioni – [email protected] 1. Introduction Active Distributed Temperature Sensing (A-DTS) is a relatively new technique that can potentially be used to monitor the soil moisture along a fibre optic (FO) cable [1,2]. Recent technological advances make it now possible to collect measurements at an unprecedented spatial resolution along cables over 1km long, making the A-DTS a promising tool for measuring the spatial variation of the soil moisture at the field scale. 2. Field case-study A field located adjacent to the BIFoR FACE forest (Norbury Junction, UK) has been selected as a field case study (Fig.1). The field is located on a gentle hill and has been recently planted with rows of deciduous saplings including English oak (Quercus robur) and sycamore (Acer pseudoplatanus). A single FO cable, approximately 1500m long, was buried in a 400m loop configuration and at three different depths (i.e. 0.10m, 0.25m and 0.40m) in between two rows of trees (Fig.2). 3. Methodology A XT DTS unit combined with a heat pulse system (both by Silixa Ltd.) have been programmed to measure temperature every 30s and at 0.25m spatial resolution. The FO cable was heated 4 times per day and the temperature cumulative increase over a period of 15min (Eq.1) has been converted to soil moisture (i.e. volumetric water content) via an empirical relationship. 4. Preliminary results The spatio-temporal variation of the soil moisture measured by A-DTS on site is shown in Fig.3b. The measurements were taken continuously over several months in 2018 and 2019 with the exception of some gaps (two of several weeks) where the heat pulse system did not restart following a power cut at the FACE facility. The results relate well with atmospheric precipitation (Fig.3a) and soil moisture measured with point sensors installed at different locations along the FO cable (Fig.3c) . In Summer 2018 a strong drying event starting in June and lasting 3 months has been successfully captured by the A-DTS. Soil moisture (VWC) Eq.1 BIFoR FACE Plantation Field DTS control unit FO DTS cable Fig.1 – Aerial view of the field site. Fig.2 – A-DTS equipment and layout. Fig.3 – a) Precipitation (mm), b) soil moisture measured by A-DTS over space and time, c) soil moisture measured by point probes along the FO cable. 5. Conclusions This study demonstrates that A-DTS is capable of monitoring soil moisture at a high spatial and temporal resolution at the field scale and for prolonged periods of times. This paves the way for monitoring soil dynamics with unprecedented detail allowing for both seasonal and event-based variations to be thoroughly investigated. 6. References [1] Gamage, D.N.V., Biswas, A., Strachan, I.B., Adamchuk, V.I., 2018. Soil Water Measurement Using Actively Heated Fiber Optics at Field Scale. Sensors 18, 1116. https ://doi.org/10.3390/s18041116 [2] Sayde, C., Gregory, C., Gil-Rodriguez, M., Tufillaro, N., Tyler, S., van de Giesen, N., English, M., Cuenca, R., Selker, J.S., 2010. Feasibility of soil moisture monitoring with heated fiber optics. Water Resour. Res. 46, W06201. https ://doi.org/10.1029/2009WR007846

Active DTS for spatio-temporal soil moisture monitoring · Active DTS for spatio-temporal soil moisture monitoring Curioni G.1, Krause S.1, Ciocca F.2 1 School of Geography, Earth

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Page 1: Active DTS for spatio-temporal soil moisture monitoring · Active DTS for spatio-temporal soil moisture monitoring Curioni G.1, Krause S.1, Ciocca F.2 1 School of Geography, Earth

Active DTS for spatio-temporal soil moisture monitoringCurioni G.1, Krause S.1, Ciocca F.2

1 School of Geography, Earth & Environmental Sciences, University of Birmingham, Birmingham, UK2 Silixa Ltd., London, UK

Contact Author: Giulio Curioni – [email protected]

1. IntroductionActive Distributed Temperature Sensing (A-DTS) is a relatively new technique that canpotentially be used to monitor the soil moisture along a fibre optic (FO) cable [1,2].Recent technological advances make it now possible to collect measurements at anunprecedented spatial resolution along cables over 1km long, making the A-DTS a promisingtool for measuring the spatial variation of the soil moisture at the field scale.

2. Field case-studyA field located adjacent to the BIFoR FACE forest (Norbury Junction, UK) has been selected as afield case study (Fig.1). The field is located on a gentle hill and has been recently planted withrows of deciduous saplings including English oak (Quercus robur) and sycamore (Acerpseudoplatanus).A single FO cable, approximately 1500m long, was buried in a 400m loop configuration and atthree different depths (i.e. 0.10m, 0.25m and 0.40m) in between two rows of trees (Fig.2).

3. MethodologyA XT DTS unit combined with a heat pulse system (bothby Silixa Ltd.) have been programmed to measuretemperature every 30s and at 0.25m spatial resolution.The FO cable was heated 4 times per day and thetemperature cumulative increase over a period of 15min(Eq.1) has been converted to soil moisture (i.e.volumetric water content) via an empirical relationship.

4. Preliminary resultsThe spatio-temporal variation of thesoil moisture measured by A-DTS onsite is shown in Fig.3b. Themeasurements were takencontinuously over several months in2018 and 2019 with the exception ofsome gaps (two of several weeks)where the heat pulse system did notrestart following a power cut at theFACE facility.

The results relate well withatmospheric precipitation (Fig.3a) andsoil moisture measured with pointsensors installed at different locationsalong the FO cable (Fig.3c) .

In Summer 2018 a strong drying eventstarting in June and lasting 3 monthshas been successfully captured by theA-DTS.

Soil moisture (VWC)

Eq.1

BIFoRFACE

Plantation Field

DTS control unit

FO DTS cable

Fig.1 – Aerial view of the field site. Fig.2 – A-DTS equipment and layout.

Fig.3 – a) Precipitation (mm), b) soil moisture measured by A-DTS over space and time, c) soil moisture measured by point probes along the FO cable.

5. ConclusionsThis study demonstrates that A-DTS is capable of monitoring soil moisture at a high spatialand temporal resolution at the field scale and for prolonged periods of times. This paves theway for monitoring soil dynamics with unprecedented detail allowing for both seasonal andevent-based variations to be thoroughly investigated.

6. References[1] Gamage, D.N.V., Biswas, A., Strachan, I.B., Adamchuk, V.I., 2018. Soil Water Measurement Using Actively Heated Fiber Optics at FieldScale. Sensors 18, 1116. https://doi.org/10.3390/s18041116[2] Sayde, C., Gregory, C., Gil-Rodriguez, M., Tufillaro, N., Tyler, S., van de Giesen, N., English, M., Cuenca, R., Selker, J.S., 2010. Feasibility ofsoil moisture monitoring with heated fiber optics. Water Resour. Res. 46, W06201. https://doi.org/10.1029/2009WR007846