Video Smoke Detection

I saw a video on YouTube's launch of an Iranian S-200 SAM, it releases a lot of smoke at first, but after a few seconds when it is high in the air, it ceases to emit smoke. How it works?

http://www.youtube.com/watch?v=BRqpr9K9k ...

If you see the video, it emits smoke during launch and even during the climb, but after 1:08 it stops releasing smoke and travel without a trace. Is it to avoid detection, such as cons-measures or what? How does it work?

A-200 S starts with 4 solid rocket boosters to the rocket. Then, the S-200 drops boosters and works on "rocket engine clean.

The smoke of four boosters launched, probably solid rocket. The smoke stops when they burn.