Compact Infrared Camera Takes Wing

Daniel C. McCarthy

The US and its allies have placed increasing emphasis on improving military reconnaissance capabilities while minimizing the risk to personnel. Combined, these demands have helped to fuel interest in unmanned aerial vehicles. These remote-piloted aircraft vary in size and shape. But the balance between payload vs. flight performance always necessitates prudent selection of onboard equipment.

This was the challenge for AeroVironment Inc. when it developed its electrically powered Pointer aircraft for military reconnaissance and law enforcement applications. The Pointer carries enough battery power to fly for over an hour, out to a range of five miles. Depending on the application, users can install a selection of cameras to relay black-and-white, color or infrared images back to the pilot. However, the Pointer's payload capacity cannot exceed 2 lb.

AeroVironment designed its Pointer unmanned aerial vehicle for military reconnaissance and law enforcement applications. Its selection of lightweight cameras includes an Indigo Systems infrared Alpha camera that weighs only 6 oz. Courtesy of AeroVironment Inc.

For some missions, the Pointer carries a color daylight-use camera that weighs only 4 oz, said Martyn Cowley, research and development marketing manager for AeroVironment. However, he noted that much reconnaissance is performed at night and that, until recently, infrared technology hasn't produced imagers comparable in weight to those for the visible range.

When missions require infrared imaging, the camera onboard the Pointer is Indigo Systems Corp.'s microbolometer-based Alpha camera. This device images between 7.5 and 13.5 µm through an 18-mm focal length lens that provides a 25° horizontal field of view. The camera, lens and electronics combined weigh 6 oz.

In the early stages of the program, the company used a Stirling-engine-cooled infrared device that weighed 2 lb. In 1995, emerging microbolometer technology enabled AeroVironment to cut that amount in half. "The microbolometer-type cameras are the latest and greatest cameras in terms of being lightweight and miniaturized and which have direct advantages to this type of aircraft," said Cowley. "For aircraft use, you can't have cameras that are too light and too small."

The weight of microbolometer chips hasn't dropped much in the past five years. The Alpha's chip has a relatively low 160 × 120-pixel count, which allowed Indigo Systems to scale down the optics, electronics and chassis, according to Stan Laband, sales manager for the company. A proprietary image-smoothing algorithm compensates for that, and the images resemble those provided by a 320 × 240-pixel chip, he added.