WASHINGTON – Look under the nose of almost any military unmanned aerial vehicle (UAV), and you’ll see a ball turret, mounted so its various sensors and emitters can pitch up and down and rotate in a full circle.

Many of these turrets now house several instruments: one or two electro-optical cameras for daylight, an infrared camera for night, and one or more laser sensors, such as a rangefinder or target designator. Controlled by a human operator — in a nearby aircraft or in a ground center half a world away — the turrets gather information and pass it on via line-of-sight radio or satellite links.

Instantaneous video, dubbed Predator TV, has become a vital part of modern U.S. warfare. Most U.S. Air Force Predator UAVs carry the Model 14 sensor payload, a 35-centimeter sphere that includes an infrared video camera and two daylight color cameras. The first is a six-step zoom camera used to detect and recognize targets; the payload operator can then switch to a second high-magnification spotter with a long-focal-length telephoto lens to help identify a target, said Steve McCann, who directs government sales for Model 14 maker L-3 Wescam, Healdsburg, Calif.

The Predators got an upgrade near the end of the 1999 Kosovo war, when the Air Force swapped one of the daylight cameras for a laser designator that could paint targets for the laser-guided bombs dropped by strike aircraft.

But the service wanted a sensor ball that did not sacrifice the second camera, and so in December 2001, it began equipping new Predators with the 43-centimeter Multi-Spectral Targeting System (MTS)-A. Built by El Segundo, Calif.-based Raytheon Space and Airborne Systems , the MTS-A carries three electro-optic and infrared cameras and a laser designator.

For the Predator B, which is one-third larger than its predecessor, the Air Force bought Raytheon’s 55-centimeter MTS-B, whose cameras can see farther than the ones in the MTS-A. Further details were withheld by the Air Force’s secretive Big Safari office at Wright-Patterson Air Force Base, Ohio, which manages the MTS programs.

L-3 Wescam also has designed a larger family of turrets, starting with the 50-centimeter MX-20, which has been installed on several kinds of manned aircraft, including the U.S. Navy P-3C Orion, Coast Guard C-130, Army Airborne Reconnaissance Low and Canadian CP-140 Aurora aircraft.

A smaller version, the 38-centimeter MX-15, was developed to suit Coast Guard HU-25 Falcon jets and later added to General Atomics’ Improved Gnat and SAIC’s Vigilante UAVs. The MX-15 carries up to six sensors, including electro-optic zoom and spotter cameras, an infrared zoom camera, laser rangefinder and laser illuminator. The cameras are a little larger than the Model 14’s and thus have higher resolution.

The infrared camera provides four fields of view: wide, midrange, narrow and very narrow. The color camera has wide, midrange and narrow magnifications; the payload operator can then switch to the spotter camera to get the very narrow field of view. The sensors are co-aligned so when the payload operator jumps from one camera to the next, the same target area is viewed. In May, the Navy began ordering some MX-15 turrets in addition to MX-20s for its P-3Cs.

The MX, MTS-A and -B all have a solid-state fiber-optic gyro mounted on their cameras. This inertial measurement unit provides better stability and target-location accuracy than earlier feedback devices, McCann said.

“The problem is, flexures (small stretching movements) occur inside the gimbal so you get some inaccuracy from those flexures,” McCann said. “Also, when you mount the gimbal on the aircraft, there is going to be some flexure and misalignment there, so when you combine the aircraft’s position information with the gimbal pointing angles, there are all kinds of inaccuracies, which result in target location error.”

Putting these measurement units right on the camera allows for much faster instructions to the servomotors that keep the cameras trained on the target, and eliminates the need to worry about the inaccuracies.

Another competitor is FLIR Systems of Portland, Ore., whose Safire infrared-camera turrets are installed in about 800 planes and 35 types of helicopters. Last August, FLIR Systems won a contract to develop an electro-optic/infrared sensor suite for the U.S. Army’s planned Aerial Common Sensor, which will be a modified Embraer ERJ-145 regional jet.

FLIR Systems’ latest turret is the 38-centimeter StarSafire 3 , introduced in June 2003. It will equip the U.S. Coast Guard’s EADS/CASA CN-235 maritime patrol aircraft and Eagle Eye tilt-rotor UAV, being developed by Bell Helicopter Textron.

The StarSafire 3 on the Eagle Eye likely will include an infrared sensor, a daylight zoom camera, a daylight spotter scope and either a laser illuminator or a laser rangefinder, or both, said Blaise Dagilaitis, FLIR Systems’ vice president for U.S. business development. It will not have a laser designator, he said.

The StarSafire 3 ‘s infrared camera features a large, advanced midwave 640-by-480 focal plane array detector producing high-resolution imagery. It has four fields of view: wide , medium , narrow and super narrow . The color daylight camera provides wide, medium and narrow fields of view.

The spotter scope, which has a haze penetration filter, matches the infrared camera’s medium- and super-narrow fields of view and also offers an ultra-narrow setting for extremely long range. The payload operator can view the medium- and super-narrow-field-of-view infrared and spotter imagery of the same scene side by side on a display screen, Dagilaitis said.

The StarSafire 3 also features an advanced image processor with scene-matching software algorithms that can fuse or combine the infrared thermal video with the spotter scope’s visible light imagery to help the operator pick out targets.

The need for smaller and lighter UAV payloads with high-performance sensors has put a premium on miniaturization of the sensors and associated electronics, more powerful optics and high-density packaging. Laser designators have become an increasing requirement for UAV payloads, so manufacturers have had to make room for them in the turrets.

Sensor features that reduce operator workload, such as auto-focusing, co-aligned cameras and automatic target tracking, are likely to become more common. The same will likely be true of embedded inertial measurement units. UAV sensors also will benefit from ongoing commercial and military advances in infrared and electro-optic cameras.