Looking for Radar Sweep suggestions

I have a need to add some 5-10 second repeatable "radar sweep" picutres to a maritime course I'm building.  It will start out as PowerPoint to be taught in class, but will migrage to Articulate when it goes E-Learning.

My concept is to have the classic green circular radar sweeping around and "renewing" the image of some channel, lake, harbor, etc.  I could then place some objects on another layer over the "radar screen" area and show how they would appear as the source of the radar (the center point ship) might move relative to another vessel somewhere on the screen.

Thanks for any suggested sources or clips you can toss my way.  We are a non-profit church and educational ministry so "free stuff" is always nice as a first choice.