Lidar vibrometry may also have potential for identifying various other targets, including ground vehicles, and even locating tunnels.
Lidar can be developed using solid-state electronics, with all the benefits this brings in miniaturization and lower costs. Radar systems can be shrunk to a couple of pounds, but future Lidar may be smaller. Vescent Photonics is working on a matchbox-sized infrared (IR) micro-Lidar. Its key innovation is to replace the mechanical beam-scanning system with an electronic one with no moving parts. When a ray of light passes through a material, the amount by which the beam is bent depends on the index of refraction of the material. The index of refraction of some liquid crystals can be changed by applying an electric current. Vescent's beam director has a waveguide with liquid crystal cladding which shifts simply by changing the applied voltage. By using the right materials and design, the device can scan an 80-deg. field of view in less than a millisecond.
The micro-Lidar combines electronic scanning with a type of laser diode known as a vertical cavity surface-emitting laser. These have limited power but can be mass-produced at low cost, and being solid-state can be integrated into a chip-scale system. Vescent's prototype micro-Lidar for the Air Armament Center should be completed this year. It is part of a larger Air Force program which aims to develop a range of compact Lidar systems, some costing less than $500 per unit and with a range of at least 500 meters (1,640 ft.).
This type of Lidar could be carried by even the smallest UAVs, providing precise 3-D imaging for collision and hazard avoidance, terrain following, landing, and target detection and tracking. The low cost and compact size would also make it suitable for new guided munitions with sophisticated target identification.
Lidar technology is still relatively immature compared to radar. Although it already provides inch-perfect topographical mapping in Afghanistan and elsewhere, there are few tactical systems. In June USAF awarded a $32 million Lidar contract to Science Application International Corp., including basic research into sources and sensors. At present it is being developed for niche applications, but these are likely to widen as the technology evolves. The pace of development suggests that Lidar's potential is only beginning to emerge.
The ISR world is also seeing the growing use of compact, relatively short-range but very-high-resolution radar. As one Israeli engineer pointed out earlier this year, radar used to be regarded as a substitute for visible light or IR sensors in bad weather—something to be used if necessary, but a poor stand-in due to its low resolution. What is now becoming appreciated is the ability of radar data to augment the visual picture, literally adding a third dimension when geo-registered and fused with IR or visual imagery. Radar is naturally good at detecting moving targets, and human-made objects—even camouflaged—often have a distinctive radar signature.
The U.S. has recently released some new radar technologies for export and announced contracts for others. Lockheed Martin has just been cleared to sell the AN/APY-12 X-band synthetic aperture radar (SAR) to a number of new customers, including Taiwan, Italy, Sweden and South Korea. A product of the Phoenix-based Lockheed Martin division that developed the first SARs in the 1950s (then Goodyear, and later Loral), the APY-12 was developed for the U.S. Army's RC-7B Airborne Reconnaissance Low surveillance aircraft and Japanese F-15 fighters carry a podded version.
APY-12 is claimed to produce “photographic quality” images, while tracking surface vehicles, taxiing aircraft and hovering helicopters in ground moving-target indication (GMTI) mode. It also has a wide-area GMTI mode and improved geolocation capability that makes it possible to search a large area for moving targets and overlay that data on a map.
Another goal for radar developers is “dismount detection”—extending GMTI to detect moving people. Raytheon was awarded a contract in July to produce four pod-mounted radar systems for the USAF, designed to be carried by the MQ-9 Reaper unmanned aerial vehicle (UAV) and intended for dismount detection.
A third relatively new U.S.-made radar is the Northrop Grumman ASQ-236, a pod-mounted ISR radar that started development in the late 1990s and is now in service on Air Force F-15Es. Information on what the 1,000-lb. pod actually does is classified, but it is identified as a Ku-band system, with an active, electronically scanned array (AESA) antenna, that “provides detailed maps for surveillance, coordinate generation and bomb impact assessment purposes.” It is the only known U.S. radar that uses a rotating “repositioner” like that built into Selex Galileo fighter radars.