What is an "annason" (VLF whistler)? I am watching the following video on software defined radio and at the beginning the narrator points out some "whistlers" on the spectrum display and says maybe they are caused by an "annason". He goes on to say that he knows "commercial annasons scan at a slower rate than the whistlers". What is an "annason". I don't know the spelling because it is verbal.

http://www.youtube.com/watch?v=ZuRcaxpbYCw
I figured out the answer. It is an "ionosondes".