Practical considerations for enhanced-resolution coil-wrapped distributed temperature sensing

Abstract

Abstract. Fibre optic distributed temperature sensing (DTS) is widely applied in Earth sciences. Many applications require a spatial resolution higher than that provided by the DTS instrument. Measurements at these higher resolutions can be achieved with a fibre optic cable helically wrapped on a cylinder. The effect of the probe construction, such as its material, shape, and diameter, on the performance has been poorly understood. In this article, we study data sets obtained from a laboratory experiment using different cable and construction diameters, and three field experiments using different construction characteristics. This study shows that the construction material, shape, diameter, and cable attachment method can have a significant influence on DTS temperature measurements. We present a qualitative and quantitative approximation of errors introduced through the choice of auxiliary construction, influence of solar radiation, coil diameter, and cable attachment method. Our results provide insight into factors that influence DTS measurements, and we present a number of solutions to minimize these errors. These practical considerations allow designers of future DTS measurement set-ups to improve their environmental temperature measurements.

Quantitative analysis of the radiation error for aerial coiled-fiber-optic distributed temperature sensing deployments using reinforcing fabric as support structure

“…7). However, we found that the maximum modeled conduction error was always smaller than temperature artifacts caused by the acrylic glass rings supporting the reinforcing fabric, which amounted to approximately 2.5 K. For a fiber cable coiled around a perforated PVC tube, Hilgersom et al (2016a) reported a mean measured conduction error of −0.4 and 0.1 K with extremes up to 0.7 K during a fog event. One must recall that in this study the conduction error was defined as the difference between the fiber temperature for open air and fiber temperature at the perforated PVC tube.…”

“…fiber-optic cable, which is limited by the along-fiber resolution of the DTS instrument to several tens of centimeters. To overcome this issue, several studies have used a support structure for helically coiling the fiber-optic cable and thus enhancing the spatial resolution up to the millimeter scale in one dimension (Selker et al, 2006;Suárez et al, 2011;Vercauteren et al, 2011;Van Emmerik et al, 2013;Euser et al, 2014;Hilgersom et al, 2016a). Recently, this idea was expanded to all three dimensions by spanning horizontal nets of fiber-optic cable across a cage (Hilgersom et al, 2016b).…”

“…Previous studies have pointed out two important issues for this approach. Firstly, coiling the fiber cable around a support structure with a very small diameter (< 3.2 cm) results in temperature artifacts at the start of the coil due to significant differential attenuation caused by the strong bending (Arnon et al, 2014;Hilgersom et al, 2016a); secondly, radiative heating of the coiled fiber-optic cable and support structure may result in substantial radiation errors up to several Kelvin, particularly for aerial applications (Selker et al, 2006;Suárez et al, 2011;Hilgersom et al, 2016a).…”

“…These rough estimates yielded conduction errors between −0.4 and 0.1 K and up to 0.7 K during a fog event. Using a simple energy balance model, Hilgersom et al (2016a) could provide some physical explanation for the observed temperature differences by the effect of the PVC tube. However, accurate estimates for the conduction error were not reported as the diameter of the tube perforations was much smaller than the spatial resolution of the DTS instrument, and the model deployed a simplified shortwave radiative transfer scheme for cloudy skies (Hilgersom et al, 2016a).…”

“…For a perforated PVC tube, Hilgersom et al (2016a) provided semi-quantitative estimates for the conduction error above water by subtracting the temperature of fiber sections crossing the perforations from the temperature of fiber sections attached to the tube. These rough estimates yielded conduction errors between −0.4 and 0.1 K and up to 0.7 K during a fog event.…”