Everything as always, back to Svalbard. The wind blew from the southwest. We flew over the cloudless east of the main island. What a great view of the sea and the glaciers. During the final approach through Adventalen it shook vigorously and the visibility was bad as there were clouds and snow.
The weather also caused delays in the set up of the masts. We shall start tomorrow, though.
Had never realized that there are airports with underfloor heating.
The measurement campaign here in Finland is unfortunately over for us. We are heading south to Helsinki, directly west to Oslo and tomorrow morning north again to the next campaign on Svalbard. This travel could in theory have been done in a much shorter time if we flew directly from Oulu to Longyearbyen.
The campaign in Hailuoto will continue until the end of February, check out the blog from GFI.
The SUMO uses an acceleration sensor, a gyro rate sensor and a GPS receiver for orientation and position. They are largely independent of external influences.
A pressure sensor for altitude measurement, a pressure tube for the velocity relative to the air or a magnetic compass for determining the orientation towards the earth is not used.
Altitude, speed (only relative the earths surface) and direction are taken only from the GPS receiver. This works as long as the SUMO moves forward so that the GPS can measure a correct direction.
This does not work for a quadcopter. It needs directional information even when it is hovering (which it is most of the time). Therefore a magnetic compass is installed. Our bebop2met is based on the Parrot Bebop2 and unfortunately the sensor in it is installed very close to the rest of the electronics, It provides imprecise data. Another problem is apparently the wide scattering of the sensors in the various individual quadcopters. In addition, we are at over 65° north and the x-y component of the earths geomagnetic vector is very small.
In the end we spend much of the day magnetically calibrating the quadcopters newly purchased for the campaign by holding and spinning the quadcopter at various angles to the earth in a dance-like performance.
The forecast has unfortunately come true and the weather was inappropriate for our measurements throughout the week. The SUMO flies profiles to collect comparison values anyway. In a cloud at 1000m we are back to the icing. The plane reverses and lands safely.
The measurements take place in parallel with several systems. For the lower 10m the mast is set up, above that the bebop2met measures from 2m to 200m, from 40m to 1800m the SUMO collects data and parallel to all that is the SODAR. At high wind speed or humidity, however, the acoustic pulse does not reach as high and the measurable altitude decreases significantly.
Somewhat troubling is water that appears close to the beach. It leads to little seas of slush ice. The locals tell us that the south wind pushes the seawater against the land and the water is pumped up.
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.