Small-Scale Measurement of Soil Water Content Using a Fiber Optic Sensor

This study is aimed to develop a real-time safety monitoring of kilometer-long joint rails using a distributed fiber optic sensor. The sensor measures the distribution of Brillouin frequency shift along its length with pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA). The measurement distance and spatial resolution can be up to 25 km and 2 cm, respectively. The fiber optic sensor was first characterized and calibrated for distributed strain and temperature measurement, and then instrumented on a small-scale joint rail-like specimen in laboratory. The specimen was loaded at room temperature, and its strain distribution along the sensor was measured using a Neubrescope with high accuracy and spatial resolution. Given a gage length, the joint open change was determined and visibly identified from the measured strain distribution. Finally, an implementation plan of distributed sensors on a railway is introduced, including sensor deployment, sensor repair when broken, and cost analysis. The gage length at a crack is an important parameter in sensor deployment and investigated using finite element analysis. The results indicate that the distributed sensor can be used successfully to monitor the strain and temperature distributions in joint rails.

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Study on calibration model of soil water content based on actively heated fiber-optic FBG method in the in-situ test

Measurement ◽

10.1016/j.measurement.2020.108176 ◽

2020 ◽

Vol 165 ◽

pp. 108176

Author(s):

Meng-Ya Sun ◽

Bin Shi ◽

Dan Zhang ◽

Jie Liu ◽

Jun-Yi Guo ◽

...

Keyword(s):

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Fiber Optic ◽

Calibration Model ◽

In Situ Test

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Imaging Rhizosphere CO2 and O2 Concentration to Localize Respiration Hotspots Linked to Root Type and Soil Moisture Dynamics

10.21203/rs.3.rs-1145795/v1 ◽

2021 ◽

Author(s):

Sarah Bereswill ◽

Nicole Rudolph-Mohr ◽

Sascha E Oswald

Keyword(s):

Soil Moisture ◽

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Lateral Roots ◽

Lupinus Albus ◽

Spatiotemporal Variability ◽

Cluster Roots ◽

Small Scale

Abstract PurposeRhizosphere respiration strongly affects CO2 concentration within vegetated soils and resulting fluxes to the atmosphere. Respiration in the rhizosphere exhibits high spatiotemporal variability that may be linked to root type, but also to small-scale variation of soil water content altering gas transport dynamics in the soil. We address spatiotemporal dynamics of CO2 and O2 concentration in the rhizosphere via non-invasive in-situ imaging.MethodsOptodes sensitive to CO2 and O2 were applied to non-invasively measure in-situ rhizosphere CO2 and O2 concentration of white lupine (Lupinus albus) grown in slab-shaped glass rhizotrons. We monitored CO2 concentration over the course of 16 days at constant water content and also performed a drying-rewetting experiment to explore sensitivity of CO2 and O2 concentration to soil moisture changes. ResultsHotspots of respiration formed around cluster roots and CO2 concentration locally increased to > 20 % pCO2 (CO2 partial pressure). After rewetting the soil, cluster roots consumed available O2 significantly faster compared to non-cluster lateral roots. In wet soil, CO2 accumulation zones extended up to 9.5 mm from the root surface compared to 0.3-1 mm in dry soil.ConclusionResults from this imaging experiment indicate that respiratory activity differs substantially within the root system of a plant individual and that cluster roots are hotspots of respiration. As rhizosphere CO2 and O2 concentration was strongly sensitive to soil water content and its variation, we recommend monitoring the soil water content prior and during the measurement of rhizosphere respiration.

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