After watching the video for about the third time, I started wondering what exactly the circle around Snake actually meant. At first I thought that it was simple as just a compass, but that didn't make any sense to me. As there were actually fluctuations in the circle itself. Being a simple compass actually doesn't make any real sense.
Then I started to notice where the fluctuations were actually pointed at. For one, The fluctuations dont "move" with snake. They actually stay in the same "direction" and move about.
THEN I NOTICED
It's actually some type of detector. It could be a bio detector, or as simple as a sound detector. But looking throught the second time, It convinced me to be a bio detector.
the higher the fluctuation from the "plane", the closer/ or the more enemy exists. I'm not exactly sure what exactly is the criteria, but it seems that it is very much an enemy radar.
some of the screens to show this.
http://students.washington.edu/nut12345/MGS4/001.jpg
Notice the first screen, The fluctuations to the left corresponds to the main battleground, while the ones on the right corresponds to the three PMCs.
http://students.washington.edu/nut12345/MGS4/002.jpg
Now this second picture has the fluctuations at the N part, which exactly corresponds to the acutal battle.
http://students.washington.edu/nut12345/MGS4/003.jpg
In this third picture, the highest fluctuation seem to reflect the armored car. the small fluctuation right in front of snake also reflects perfectly the position of the soldier in front.
http://students.washington.edu/nut12345/MGS4/004.jpg
in this last picture, the fluctuation pointing to the lower right obviously marks the friendlies (or at least in this situation) hiding behind the sand bag.
The Large fluctuations to the south, then, I suppose symbolizes the 2 guys up on top and the three guys coming out of behind the drums, which you will have to see the gameplay video itself to know.
There are a lot more examples, and I could post one for each time the fluctuations come out to demonstrate the idea. But I'd say that looking at the video itself again with this "bio detector" in mind would make a lot more sense than looking at the pictures I've posted. Once I started seeing the fluctuations correspond to moving people, it makes that ring make a lot more sense
This, IMO, is MUCH more useful as a radar