If you squint at the laptop in the video, you can see that his geiger counter is reading over 400 CPM!
Christoph sent me his data logs, which clearly show the effect of altitude on radiation exposure:
The red trace is the background level on the ground in SFO and hovers around 20 CPM. The blue trace is the measured radiation over Greenland on his transatlantic flight. The peak readings are 25 times the background radiation at sea-level!
Caution: Unless you like being hassled by the TSA, I don’t recommend flying with the Geiger kit in your carry-on luggage, much less actually using it on the plane! On his DIY Geiger Counter site, Brohogan posted some good advice about traveling with a Geiger counter.
Have you done something cool with your Geiger Counter kit? If so, post about it in the forums!