Eyes in the Sky

The first implementation of automatic dependent surveillance-broadcast (ADS-B) in Canada was in January 2009 in the airspace over Hudson Bay. With no existing radar, there had been a surveillance gap of 850,000 square kilometres. Nav Canada installed five ADS-B receiving stations on the ground at various locations around the shores of the Bay, to close that gap and provide coverage.

http://skiesmag.com/news/article/EyesintheSky