NATO is keeping a close eye on events in Ukraine, using surveillance planes to patrol along the edges of Poland and Romania.

As the CBC's Jeff Semple reports from an airbase in western Germany, NATO is employing an AWACS-equipped Boeing 707 — notable for the large, rotating dish that rides on top, just ahead of the tail fin — to watch Russian troop movements in the region.

"They're doing training exercises as well, so we're monitoring that," says Canadian Major Charles Riffou, pointing at the radar map on his computer screen.

"They also have some large ships in the area that are listening, and are reporting what the other side is doing. So it's kind of a cat-and-mouse game right now."

The tools aboard the Airborne Warning and Control System plane provide the crew with radar images of land, sea and air reaching out some 400 kilometres, Semple reports.

"It's the reassurance for our NATO allies that there is an eye in the sky watching what's going on," says the pilot, Lt.-Col. Peter Lowerse of the Netherlands.

NATO has tripled the number of aircraft now based in the Baltic states in response to the continuing crisis in Ukraine, Semple reports.