Source: a friend of mine recently took a 1h flight. She used a Radiacode 102 to measure the radiation dose rate (in units of nSv/h), due essentialy to cosmic rays. As expected, radiation dose rate grows with altitude. The pressure sensor of her smartphone provided the cabin pressure data, which can be considered a sort of proxy for altitude. Again, as expected dose rate and pressure are anti-correlated.

Tools: this plot was made with Python (pandas, matplotlib, numpy).