Evaluation of the effects of direct solar radiation on fiber-based distributed temperature sensing

Accurate and precise measurements of microclimatic temperatures are important for understanding microclimate dynamics within forests, which are crucial in the face of climate change. Various methods exist for measuring microclimate temperatures in the field; however, for ultra-high-resolution measurements in space (< 1 m) and time (< 1 minute), optical fiber-based sensing systems become a promising option. Specifically, a Distributed Temperature Sensing (DTS) system coupled with a fiber over 100 – 1000m long could be highly suitable to collect spatial temperature data continuously in forests and other vegetation types. Although DTS is accurate in controlled lab conditions, the impacts of environmental factors such as energy fluxes from direct solar radiation on temperature measurements remain to be quantified. Given the environmental variability in forest ecosystems, it is essential to take into account the increase in fiber temperatures due to solar radiation. Here we explore the impact of radiative fluxes from direct sunlight on the optical fibers used in DTS systems. To evaluate the impact of radiative fluxes on the thermal accuracy of a DTS, we conducted a field experiment with direct solar radiation. We put two fiber regions under the same condition, but one region is coated with aluminum while the other one is uncoated. We observed distinct thermal responses between aluminum-coated and uncoated sections of the optical fibers when exposed to solar radiation, with the uncoated fiber exhibiting a higher temperature under the same conditions. Our results can be used to mitigate this bias in field measurements, enhancing the accuracy of DTS in environmental monitoring, and deepening our understanding of the effects of solar radiation on fiber-based remote sensing technologies.