They're tracked by Canada's Radarsats (8)
I believe the answer is:
icebergs
'they're tracked by canada's radarsats' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for icebergs that I've seen before include "Arctic sea hazards" , "Large masses floating at sea in polar regions" , "Masses of ice floating at sea" , "Large masses of frozen water" , "Huge masses of frozen water" .)