As popular as UAVs are, blimps provide most of the aerial surveillance over Iraq and Afghanistan. The larger UAVs are popular mainly for their mobility and persistence (the ability to stay in the air, over a particular area, for a long time.) Predator and Global Hawk can stay in the air for over 24 hours at a time. Controllers and observers, operating, via satellite link, from bases in the U.S., see that the video and radar images get passed on to the people that need them. But the military has found that "stationary UAVs" (helium filled aerostats or tall towers) not only do the job, but do it a lot cheaper (under $1000 an hour, mostly for maintenance, repairs and personnel to monitor the sensors) and stay airborne nearly all the time. Compare this to Predator, which costs $6,000 an hour to fly, and Global Hawk, which 4-5 times more. Global Hawk is so expensive partly because of the high end sensors used. Not everyone needs the high flying Global Hawk, or even a Predator. They just need a way to keep an eye on a large area (like a chunk of the Syrian, Iranian or Pakistani border, or the area surrounding a base) 24/7. The PTDS (Persistent Threat Detection Systems) that are mounted in the aerostats or towers are a much cheaper alternative to mobile UAVs.
All this is a recent development. Six years ago, U.S. Army sent 22 blimps (aerostats, actually) to Iraq and Afghanistan. The most common model of aerostats float at about 330 meters (a thousand feet) up, tethered by a cable that provides power and communications to the day and night cameras up there. The big problem was ground fire from rifles and machine-guns. Hostile gunmen liked using the aerostats as targets. Rifle fire would not destroy the aerostats, but did cause them to be brought down more frequently for repairs. Normally, the aerostats can stay up for 30 days at a time, but the bullet hole repairs have some of them coming down every few days. The PTDS surveillance systems mounted on tall steel towers also suffer gunfire damage, but rarely any that disables the equipment.
The first army aerostats went to Iraq in early 2004, where they were used to help defend offshore oil facilities from attack by terrorist speedboats. Those early systems used a 233 foot long, helium filled, unmanned aerostat equipped with radar and other sensors. These aerostats were about 2.5 times the size as the more familiar advertising blimp. Aerostats are blimp like vehicles designed to always turn into the wind and stay in the same place. These larger aerostats were originally designed to detect cruise missiles, and were soon replaced by smaller and cheaper aerostat systems currently in use.
These smaller PTDS systems were much cheaper, less than five million dollars each, and the army has bought several hundred of them. These PTDS systems used aerostats as well as towers. The aerostat, operating at 330 meters, could see out to about sixty kilometers. The smaller towers shorten that range quite a bit. The 30 foot tower can see out to eleven kilometers, the 60 foot tower out to 16 kilometers and 84 foot tower out to 20 kilometers. The 30 foot tower is adequate for most situations, which usually involve guarding a base.
The early PTDS aerostat systems were operated by air defense troops, often from the reserves or National Guard. Over the last six years, the sensors carried have improved, with several day/night vidcams on board, each with zoom capability. A laser range finder is also carried, along with GPS, enabling PTDS to get an exact location of anything suspicious out there. In an area like Afghanistan, where camps are often surrounded by hills and not much else, PTDS is a critical element in the security system that keeps the bases safe, and provides air reconnaissance for any troops operating within range of the aerostats cameras. Some aerostats also carry communications transponders, giving troops more reliable radio communications.