Distributed observations of wind direction using microstructures attached to actively heated fiber-optic cables

Lapo, Karl; Freundorfer, Anita; Pfister, Lena; Schneider, Johann; Selker, John S.; Thomas, Christoph

doi:10.5194/amt-13-1563-2020

Cited by 18 publications

(10 citation statements)

References 24 publications

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“…L ↓ and L ↑ (W m −2 ) are the average downward and upward longwave radiation fluxes, respectively, and is the FO cable surface emissivity. Based on the kind of stainless steel, emissivity values can range from 0.3 to 0.7 (Baldwin and Lovell-Smith, 1992); however, we assume a value of 0.5 (Madhusudana, 2000). σ is the Stefan-Boltzmann constant, 5.67 × 10 −8 (W m −2 K −4 ), and σ T 4 s is the outgoing longwave radiation of the fiber, i.e., L fiber ; h is the convective heat transfer coefficient (W m −2 K −1 ).…”

Section: Dts and Signal-to-noise Ratio Analysismentioning

confidence: 99%

Revisiting wind speed measurements using actively heated fiber optics: a wind tunnel study

et al. 2020

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Abstract. Near-surface wind speed is typically only measured by point observations. The actively heated fiber-optic (AHFO) technique, however, has the potential to provide high-resolution distributed observations of wind speeds, allowing for better spatial characterization of fine-scale processes. Before AHFO can be widely used, its performance needs to be tested in a range of settings. In this work, experimental results on this novel observational wind-probing technique are presented. We utilized a controlled wind tunnel setup to assess both the accuracy and the precision of AHFO under a range of operational conditions (wind speed, angles of attack and temperature difference). The technique allows for wind speed characterization with a spatial resolution of 0.3 m on a 1 s timescale. The flow in the wind tunnel was varied in a controlled manner such that the mean wind ranged between 1 and 17 m s−1. The AHFO measurements are compared to sonic anemometer measurements and show a high coefficient of determination (0.92–0.96) for all individual angles, after correcting the AHFO measurements for the angle of attack. Both the precision and accuracy of the AHFO measurements were also greater than 95 % for all conditions. We conclude that AHFO has the potential to measure wind speed, and we present a method to help choose the heating settings of AHFO. AHFO allows for the characterization of spatially varying fields of mean wind. In the future, the technique could potentially be combined with conventional distributed temperature sensing (DTS) for sensible heat flux estimation in micrometeorological and hydrological applications.

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Section: Dts and Signal-to-noise Ratio Analysismentioning

confidence: 99%

Revisiting wind speed measurements using actively heated fiber optics: a wind tunnel study

et al. 2020

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“…Indeed, the difference of temperature measured between an electrically heated and a non-heated FO cable is directly dependent on water fluxes (Bense et al, 2016;Read et al, 2014;Sayde et al, 2015), offering the possibility to determine fluxes and their spatial distribution over a large range with an excellent accuracy (Simon et al, 2021). Active heat tracer experiments using fiber-optic DTS have been used to estimate wind speed in the low atmosphere (Lapo et al, 2020;Sayde et al, 2015), in dam monitoring (Ghafoori et al, 2020;Perzlmaier et al, 2004;Su et al, 2017), for groundwater fluxes measurements in open (Banks et al, 2014;Klepikova et al, 2018;Read et al, 2014Read et al, , 2015 and sealed boreholes (Munn et al, 2020;Selker and Selker, 2018) or else in direct contact within sedimentary aquifers (del Val et al, 2021;des Tombe et al, 2019). Despite promising developments, active-DTS methods have been seldom used in hydrology to estimate groundwater/surface water interactions.…”

Section: Introductionmentioning

confidence: 99%

Combining passive- and active-DTS measurements to locate and quantify groundwater discharge into streams

Simon

Bour

Faucheux

et al. 2021

Preprint

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Abstract. FO-DTS (Fiber Optic Distributed Temperature Sensing) technology has been widely developed to quantify exchanges between groundwater and surface water during the last decade. In this study, we propose, for the first time, to combine long-term passive-DTS measurements and active-DTS measurements in order to highlight their respective potential to locate and quantify groundwater discharge into streams. On the one hand, passive-DTS measurements consist in monitoring natural temperature fluctuations to detect and localize groundwater inflows and characterize the temporal pattern of exchanges. Although easy to set up, the quantification of fluxes with this approach often remains difficult since it relies on energy balance models or on the coupling of distributed temperature measurements with additional punctual measurements. On the other hand, active-DTS methods, recently developed in hydrogeology, consist in continuously monitoring temperature changes induced by a heat source along a FO cable. Recent developments showed that this approach, although more complex to set up than passive-DTS measurements, can address the challenge of quantifying groundwater fluxes and their spatial distribution. Yet it has almost never been conducted in streambed sediments. In this study, both methods are combined by deploying FO cables in the streambed sediments of a first- and second-order stream within a small agricultural watershed. A numerical model is used to interpret passive-DTS measurements and highlight the temporal and spatial dynamic of groundwater discharge over the annual hydrological cycle. We underline the difficulties and the limitations of deploying a single FO cable to investigate groundwater discharge and show the impact of uncertainty on sediments thermal properties on the quantification of groundwater inflows. On the opposite, the active-DTS experiment allows estimating the spatial distribution of both the thermal conductivity and the groundwater flux at high resolution with very low uncertainties all along the heated section of FO cable. Our results highlight the added values of conducting active-DTS experiments, eventually combined with passive-DTS measurements, to fully investigate and characterize patterns of groundwater-stream water exchanges at the stream scale. The combination of both methods allows discussing the impact of topography and hydraulic conductivity variations on the variability of groundwater inflows in headwater catchments.

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“…The cable jacket adds surface and volume, making the measurement more susceptible to the local energy balance terms (Thomas et al, 2012;de Jong et al, 2015). Hence, micro-meteorological studies with DTS have primarily been demonstrated for conditions of nocturnal darkness (Keller et al, 2011;Thomas et al, 2012;Zeeman et al, 2015) or, after adjustments, taking advantage of a differentiating thermal signal governed by wind, evaporation or shading of sunlight (Petrides et al, 2011;Euser et al, 2014;Sayde et al, 2015;Lapo et al, 2020;Schilperoort et al, 2018;van Ramshorst et al, 2020). Fibre-optic cable can be deployed to form a mesh of horizontal and vertical profiles in complex geometries from the ground up.…”

Section: Introductionmentioning

confidence: 99%

Use of thermal signal for the investigation of near-surface turbulence

Zeeman

2021

Preprint

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Abstract. Organized motions in the roughness sub-layer were investigated using novel temperature sensing and data science methods. Despite accuracy draw backs, current fibre-optic temperature (DTS) and thermal imaging (TIR) instruments offer frequent, moderately precise and highly localized observations of thermal signal in a domain geometry suitable for micro-meteorological applications near the surface. Horizontal and vertical cross-sections allowed a tomographic investigation of the spanwise and streamwise evolution of organised motion, opening avenues for analysis without assumptions on scale relationships. Variance events on the order of seconds to minutes could be identified, localized, and classified using signal decomposition and machine learning techniques. However, small-scale turbulence patterns at the surface appeared difficult to resolve due to the heterogeneity of the thermal properties of the vegetation canopy, which are not immediately evident with the naked eye. The results highlight a need for physics-aware data sciences techniques that treat scale and shape of temperature structures in combination, rather than as separate features.

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Distributed observations of wind direction using microstructures attached to actively heated fiber-optic cables

Cited by 18 publications

References 24 publications

Revisiting wind speed measurements using actively heated fiber optics: a wind tunnel study

Revisiting wind speed measurements using actively heated fiber optics: a wind tunnel study

Combining passive- and active-DTS measurements to locate and quantify groundwater discharge into streams

Use of thermal signal for the investigation of near-surface turbulence

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