Distributed temperature sensing (DTS) measurements have been running at the Hyytiälä forest site since May 2019 and the measurement campaign is projected to end late autumn 2019. The DTS measurements provide continuous temperature data along a fibre optic cable and the cable can be distributed freely in the measurement area. The data can be acquired at 1 Hz and 12 cm resolution along the cable which enable us to study the dominant turbulent eddies and other flow modes. In this campaign we attached the cable to the 125 m tall mast and also horisontally between two masts within the forest. Altogether a few kilometres of cable is being used providing us with ample information on the temperature distribution within and above the forest. These measurements hopefully shed light on the low mixing conditions occurring at night which are notoriously difficult for micrometeorological flux measurements.