A week after NATO began sending its AWACS aircraft to monitor aircraft activity over northern Libya, it's been decided to have these radar aircraft monitor that airspace 24/7. The AWACS can fly over international waters and still monitor air activity several hundred kilometers into Libya. This may become crucial if a no-fly zone is established over the Libyan coastal area (where most of the population lives). AWACS can spot Libyan aircraft taking off, and call in fighters to deal with that problem before the Libyan warplanes can get very far.
The Libyan rebels resisted calling for a no-fly zone, but recent defeats have changed their minds. The Arab League has also called on the UN to authorize a no-fly zone, and the U.S. has agreed to participate. American and French carriers, plus, possibly, Egyptian fighters, would provide the combat aircraft needed for enforcement. While Libya doesn't have many flyable warplanes, the few they do get into the air have proved to be powerful weapons against the rebels. In at least three cases, Libyan pilots refused to bomb the rebels. The pilots of two aircraft defected and flew to Malta. The two crew in another fighter-bomber ejected and let their aircraft crash. It's believed that Libyan dictator is now using mercenary pilots (perhaps from Syria).
Several nations are also using their spy satellites to monitor what's going on down there, and some of that information is probably making its way to the rebels. But the AWACs, first introduced in the 1980s, has proved the most effective way to obtain a constant view of the air in combat zones.