A simple wind measurement control loop was written for the Bebop2 quadcopter. It tries to keep the roll angle at zero to align with the wind. It works well if there is a certain wind speed and clear, non-turbulenced wind. The wind speed is going to be determined later from the pitch angle.
The SODAR is set up. An array of loudspeakers pushes a very loud, audible series of pulses into the air and receives the response from the atmosphere with microphones.
The wind direction and wind speed can be determined based on the reflections at the air layers (having a different temperature).
At noon a cloud layer starts to cover the sky. It starts to snow in the afternoon. During supper we see that the weather should stay like that the rest of the week. There is some chance that a time window might open again during the night.
The measurements require a stable boundary layer. Clear skies without clouds and cold air would be ideal. We prepare for flights in the night, but in the end we don’t. In between we watch the rocket launch.
We are back in northern Finland (a report from the first trip will follow below). This is part of a measurement campaign over the sea ice of the Gulf of Bothnia (the northern continuation of the Baltic Sea), next to the island of Hailuoto.
Last year we could drive over the ice with the car. This year it is too weak (25cm instead of the required 40cm). We take the free ferry. 3MW of diesel-electric power push it through the broken ice. Only 30cm of water are under the keel at some points. You can see the lights from an icebreaker on the horizon. It is waiting to help ships loaded with wood from Oulu.
The unfriendly weather in Germany called for a de-icing of the aircraft. Here in the north it is crisp cold at -12°C. Just as winter must be.