Distributed sensing of wind direction using fiber-optic cables

Abstract

In the atmospheric boundary layer, phenomena exist with challenging properties such as spatial heterogeneity, particularly during stable weak wind situations. Studying spatially heterogeneous features requires spatially distributed measurements on fine spatial and temporal scales. Fiber-Optic Distributed Sensing (FODS) can provide spatially distributed measurements, simultaneously offering a spatial resolution on the order of decimeters and a temporal resolution on the order of seconds. While FODS has already been deployed to study various variables, FODS wind direction sensing has only been demonstrated in idealized wind tunnel experiments. We present the first distributed observations of FODS wind directions from field data. The wind direction sensing is accomplished by using pairs of actively heated fiber optic cables with cone-shaped microstructures attached to them. Here we present three different methods of calculating wind directions from the FODS measurements, two based on using combined wind speed and direction information and one deriving wind direction independently from FODS wind speed. For each approach, the effective temporal and spatial resolution is quantified using spectral coherence. With each method of calculating wind directions, temporal resolutions on the order of tens of seconds can be achieved. The accuracy of FODS wind directions was evaluated against a sonic anemometer, showing deviations of less than 15° most of the time. The applicability of FODS for wind direction measurements in different environmental conditions is tested by analysing the dependence of FODS wind direction accuracy and observable scales on environmental factors. Finally, we demonstrate the potential of this technique by presenting a period that displays spatial and temporal structures in the wind direction.

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“…To improve understanding of in-canopy energy exchange, measuring in-canopy wind velocities will be an important requirement. New developments in wind sensors like Freundorfer et al (2021) and Alveringh et al (2022) open a promising avenue for further research.…”

Toward quantifying turbulent vertical airflow and sensible heat flux in tall forest canopies using fiber-optic distributed temperature sensing

“…This method was developed and tested in the wind tunnel with . Subsequently, Freundorfer et al (2021) successfully deployed this method for measuring horizontal wind direction in their field experiment. This study used the same method to measure the wind direction but in a vertical direction using a cylindrical shroud around coned fibers.…”

“…The before-mentioned study was conducted in ideal-ized wind tunnel experiments. Very recently, Freundorfer et al (2021) deployed this approach for the first time during actual field observation. They presented three different methods of calculating turbulent horizontal wind directions from the FODS measurements, indicating the potential of this approach to reveal the wind direction's spatial structures at scales of meters and tens of seconds.…”

Toward quantifying turbulent vertical airflow and sensible heat flux in tall forest canopies using fiber-optic distributed temperature sensing

“…This method was developed and tested in the wind tunnel with Lapo et al (2020). Subsequently, Freundorfer et al (2021) successfully deployed this method for measuring horizontal wind direction in the field experiment.…”

“…The beforementioned study was conducted in idealized wind tunnel experiments. Very recently, Freundorfer et al (2021) deployed this approach for the first time during actual field observation. They presented three different methods of calculating horizontal wind directions from the FODS measurements, indicating the potential of this approach to reveal the wind direction spatial structures at scales of meters and tens of seconds.…”