Calibrated DTS data, Maisbich, 2009-03

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: Tidbit Distance(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 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.

校准光纤分布式温度传感（Distributed Temperature Sensing，DTS）数据，卢森堡Maisbich地区
父项：校准光纤分布式温度传感（DTS）数据，Maisbich地区

卢森堡Maisbich河DTS导出温度的校准流程说明。请注意，该校准仅修正源自DTS设备（英国Sensornet公司Halo型号）的偏移，不修正电缆未完全浸没于溪流中的时段误差。

DTS获取的温度通过5个独立温度记录仪（TidbiT v2 Temp logger，美国HOBO公司）进行校准，这些记录仪沿电缆分布，距DTS台式计算机的距离分别为26米、395米、931米、1111米和1270米。需注意，研究分支位于距台式计算机717米（V型缺口堰Q3）至1282米（V型缺口堰Q4）之间。

对于每个以6分钟间隔测量的TidbiT温度记录仪，在2008年4月4日至2008年12月4日期间，确定了DTS导出温度与TidbiT和DTS导出温度差值之间的线性关系（dT = a*T_DTS + b）。针对每个TidbiT位置，计算得到斜率（a）和偏移量（b）如下：

TidbiT记录仪 距离（米） 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，推导了距DTS台式计算机的距离与斜率（a_slope + b_slope*X）、距离与偏移量（a_offset + b_offset*X）之间的线性关系，得到偏移量作为距离和DTS导出温度的函数。随后，将该偏移量加到初始DTS导出温度中，校准温度公式为：
Tcal = T_DTS + (a_slope + b_slope*X)*T_DTS + (a_offset + b_offset*X)
其中参数值为：
a_slope：0.085
b_slope：1.78e-005
a_offset：-1.16
b_offset：8.03e-004

最后一步，将距离反转，以上游V型缺口堰Q4为0米。仅显示V型缺口堰Q4（0米）至Q3（565米）之间的部分。

测量仪器：卢森堡Maisbich地区光纤分布式温度传感器（DTS）

光纤分布式温度传感（DTS）系统可测量整个溪流的水温，由一台内置数据采集与处理软件的专用台式计算机及连接的光纤电缆组成。系统向光纤电缆中发送短激光脉冲（约几纳秒量级）；当光照射到物质时，小部分光会被反射。由于玻璃中的光速已知，通过测量激光脉冲发送时刻与反射光子返回时刻之间的时间差，可确定反射位置。该系统由英国Sensornet公司生产（型号Halo），空间分辨率为2米，时间分辨率为3分钟，此配置下精度约为0.1℃。