Calibrated DTS data, Maisbich, 2009-05

Calibrated fibre optic Distributed Temperature Sensing (DTS) data, Maisbich, Luxemburg Parent item: Calibrated fibre optic Distributed Temperature Sensing (DTS) data, Maisbich Explanation of the calibration procedure of the DTS derived temperatures in the Maisbich river, Luxembourg. Note that it only corrects offsets orriginating from the DTS device (Halo, Sensornet, UK). It does NOT correct for periods when the cable is not properly submerged in the stream. The DTS obtained temperatures were calibrated with five independent temperature loggers (TidbiT v2 Temp logger, HOBO, USA) located along the cable at 26, 395, 931, 1111 and 1270 m from the DTS desktop computer, respectively. Note that the investigated branch lies between 717 (V-notch weir Q3) and 1282 m (V-notch weir Q4) from the desktop computer. For each Tidbit temperature logger, which measured at a 6 min interval, a linear relation was determined between the DTS derived temperature and the difference between the TidbiT and DTS derived temperature for the period 4-Apr-2008 until 4-Dec-2008 (dT = a*T_DTS + b). For each Tidbit location a slope (a) and an offset (b) was determined: TidbitDistance(m)ab T coolbox26-1.310,0974 T road395-0.490,0664 T Mai171u931-0.690,122 T Mai11u1111-0.250,109 T Q4-21270-0.0560,0965 Then a lineair relation between distance from the DTS desktop computer and slope (a_slope + b_slope*X), and between distance from desktop computer and offset (a_offset + b_offset*X) was derived, resulting in an offset as a function of distance and DTS derived temperatures. Subsequently, this offset was added to the initial DTS derived temperatures. Tcal = T_DTS + ( a_slope + b_slope*X)T_DTS + (a_offset + b_offset*X) with: a_slope :0.085 b_slope :1.78e-005 a_offset:-1.16 b_offset:8.03e-004 In the last step the distance was reversed, with the upstream V-notch weir Q4 at 0 m. Only the part between V-notch weirs Q4 and Q3 (at 565 m) are shown. Measuring instrument: Fibre optic Distributed Temperature Sensor DTS, Maisbich, Luxemburg The fibre optic Distributed Temperature Sensing (DTS) system measures the water temperature along the entire stream. It consists of a dedicated desktop computer with built-in data-acquisition and processing software, to which a fibre optic cable is attached. Short laser pulses (in the order of a few nanoseconds) are sent through the fibre optic cable. When light strikes matter a small portion of the light may be reflected. By measuring the time between the moment the laser pulse is sent through the cable and the moment a reflected photon comes back, the location of reflectance can be determined, since the speed of light in glass is known. The system is from Halo, Sensornet, UK, and has a spatial resolution of 2 m and a temporal resolution of 3 min. This configuration results in a precision of ∼0.1◦C.

卢森堡Maisbich流域校准型光纤分布式温度传感（Distributed Temperature Sensing, DTS）数据集。父数据集：卢森堡Maisbich流域校准型光纤分布式温度传感（DTS）数据集。
本数据集附带卢森堡Maisbich河流域DTS反演温度的校准流程说明。请注意，本次校准仅修正源自DTS设备（英国Sensornet公司Halo型号）本身的系统偏移量，未对光纤缆线未完全浸没于溪流中的时段进行校正。
本次通过DTS反演得到的水温，通过沿光纤缆线布设的5台独立温度记录仪完成校准，这5台记录仪分别位于距离DTS台式主机26 m、395 m、931 m、1111 m及1270 m的位置，设备型号为TidbiT v2型温度记录仪（HOBO，美国）。需说明的是，本次研究的河道分支范围为距离台式主机717 m（V形缺口堰Q3）至1282 m（V形缺口堰Q4）之间的河段。
每台TidbiT记录仪均以6分钟为间隔采集数据，针对2008年4月4日至2008年12月4日的时段，我们建立了DTS反演水温与TidbiT实测水温和DTS反演水温差值之间的线性关系（dT = a*T_DTS + b）。针对每台记录仪的布设位置，我们分别得到了斜率(a)与截距(b)参数：
| TidbiT位置 | 距离(m) | a | b |
|------------|---------|-------|--------|
| T coolbox | 26 | -1.31 | 0.0974 |
| T road | 395 | -0.49 | 0.0664 |
| T Mai171u | 931 | -0.69 | 0.122 |
| T Mai11u | 1111 | -0.25 | 0.109 |
| T Q4-2 | 1270 | -0.056| 0.0965 |
随后，我们进一步建立了布设距离与斜率（拟合形式为a_slope + b_slope*X）、布设距离与截距（拟合形式为a_offset + b_offset*X）之间的线性关系，最终得到以布设距离和DTS反演水温为变量的偏差校正公式。将该校正偏差叠加至初始DTS反演水温后，即可得到校准后的水温：
T_cal = T_DTS + (a_slope + b_slope*X)·T_DTS + (a_offset + b_offset*X)
其中参数取值为：
a_slope: 0.085
b_slope: 1.78×10^-5
a_offset: -1.16
b_offset: 8.03×10^-4
在最终处理步骤中，我们将距离基准反转，以位于上游的V形缺口堰Q4作为0 m起点。本次数据集仅展示了V形缺口堰Q4与Q3（间距为565 m）之间的河段数据。
测量仪器：卢森堡Maisbich流域光纤分布式温度传感（DTS）系统
本光纤分布式温度传感（DTS）系统可沿溪流全长获取水温数据。该系统由搭载专用数据采集与处理软件的台式主机及连接的光纤缆线组成。系统通过向光纤缆线发送纳秒级的短激光脉冲实现测温：当光线照射到介质时，会有一小部分光发生背向散射；通过测量激光脉冲发射时刻与背向散射光子返回时刻的时间差，结合玻璃介质中的光速已知值，即可确定背向散射点的空间位置。本系统采用英国Sensornet公司的Halo型号设备，空间分辨率为2 m，时间分辨率为3 min，测量精度约为0.1℃。