The contribution of citizen observers to the UHU lightning and TLE observation campaign on the International Space Station in 2025

The UHU experiment (uhu.epss.hu) was conducted on the International Space Station (ISS) from 26 June to 14 July, 2025 to observe lightning activity and transient luminous events (TLEs) from space using a commercial color video camera. Several months before the mission, a call was issued seeking contribution to this experiment in the form of ground-based optical observations. One aim of the supporting ground campaign was to increase the chance of capturing one or more TLE from space and from the ground simultaneously, and use the respective images to quantify the effect of different propagation through the atmosphere on the recorded color and brightness distribution of the events. Although simultaneous observation of TLEs was not achieved eventually during the campaign, the attempt showed the currently already significant potential of the community of observers in supporting scientific missions targeting optical observations on a global scope. The result that TLEs were observed by contributors above thunderstorms which were also marked for the astronauts on the ISS as possible targets, validates the concept of the open call. The campaign has also provided useful experience that can be utilized in similar calls in the future to further increase the effectiveness of such activities and the scientific value of the collected observations. In this contribution, the preliminary results of the UHU ground-based optical observation campaign are summarised and the gained experiences are presented.