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.