Canada just signed a A$2.5 billion deal with Australia for a radar system that bounces high-frequency radio waves off the ionosphere and uses the upper atmosphere as a mirror to see aircraft, ships, and missiles up to 3,000 kilometers away. July 1st, which is also Canada Day, marks official start of work on the radar project in Canada. In this video: why conventional radar has a physics problem that the Arctic exposes ruthlessly, how over-the-horizon radar uses the ionosphere to see past the curve of the Earth, why Canada chose Australian technology over U.S. alternatives, what this means for NORAD and the Five Eyes alliance.