Sensor technology is increasing in importance as forces demand a more integrated, continuous picture of the enemy's disposition and movements

One of the key drivers for the US Air Force's future strategy is the shift to expeditionary forces able to deploy rapidly anywhere worldwide. This drives technology development programmes at the AFRL.

As part of this shift, the USAF is reviewing the assets which need to be deployed; those which can remain in continental USA, with deployed forces "reaching back" to access them; and those which, while US-based, can globally provide information to both deployed and US-located commanders and forces.

One of the Sensors Directorate's (SN) principal tasks is to produce a communications network so that "everybody has the same view", says Ron Kaehr, technical director, strategic planning. Without every commander having the same intelligence picture, command and control (C2) becomes muddled and precision engagement becomes difficult.

SN's technology acquisition, says Kaehr, includes development of radio frequency (RF) sensors - predominately radar - and countermeasures; electro-optical sensors - including laser radar - and countermeasures; model-based automatic target recognition and sensor fusion. It is also participating in the development of anti-jam GPS satellite-navigation systems.

To ensure that the directorate provides what is required "we continually talk to the warfighter about ISR [intelligence, surveillance and reconnaissance], precision engagement and electronic warfare," he says, adding that the best measure of SN's success will be if there is "no sanctuary for the enemy".

Reaching back to the USA will require high capacity, secure communications links. Kaehr says it is safe to assume that there will be more unmanned equipment in the inventory - space-based and UAV ISR assets, stand-off precision-guided munitions and UCAVs. All will need more capable sensors. Potentially, all sensor images will be combined, available to commanders in theatre and those in the war rooms back in the USA.

A key programme in SN's technology drive is the Sensor Craft, which Kaehr describes as similar to an automobile manufacturer's concept car - "designed to get the audience's reaction" (see box P42). It is an across-AFRL effort with input from materials, munitions, directed energy, propulsion, air vehicles, space vehicles and information specialists.

SN's senior electronics engineer Ron Crumbacher says the Sensor Craft vision is to "provide the warfighter with the eyes and ears to respond to dynamic combat operations with the right force on target". He believes it would rejuvenate USAF ISR capabilities.

The Sensor Craft combines a variety of emerging technologies into a UAV capable of operating at high altitude in all weathers for extended periods; a 60h baseline mission is envisaged with a plan to push endurance to 80h. Long endurance requires fewer aircraft while sustained presence allows the enemy to be monitored continually, eliminating problems such as those encountered in Kosovo last year when it was known Serb forces had deployed but not to where because ISR was not continuous.

In future, ISR will encompass today's satellites, UAVs such as Predator and Global Hawk, the Joint Surveillance and Target Attack Radar System, Airborne Warning and Control System, reconnaissance platforms such as the Lockheed Martin U-2 and intelligence systems such as the Boeing RC-135. But it will add more satellites, the Sensor Craft, advanced versions of today's UAVs and possibly UCAV derivatives, swarming mini/micro UAVs and unattended ground sensors (UGS). Air, space and ground ISR components will be linked together within an "infocentric infrastructure", says Crumbacher. He says the Sensor Craft is considered a medium-term development in fiscal years 2007-13 with an initial operational capability from 2018.

Interim step

Crumbacher says an interim single-band system combining synthetic aperture radar, ground moving target indication, electronic support measures and air moving target indication (SAR/GMTI/ESM/AMTI) could be integrated into current platform from 2006 for operational assessment.


The system will be able to integrate the data from a variety of platforms, and to adapt sensor management to allow complex tasks such as finding and identifying "extremely difficult camouflaged, concealed and deceived [CC&D] targets". Crumbacher says the system will be multi-static (illuminating targets for other receivers and receiving reflected energy from other emitters) with space assets and "up-close and personal" UGS.

RF sensors would include radar and ESM integrated into the airframe. ESM would be split into high and low bands while radar functions would include AMTI, GMTI, SAR and foliage penetration SAR - operating across multiple-bands and in monostatic or bistatic modes. Multi/bistatic operation allows the receiver to remain passive.

Electro-optical sensors would include infrared search and track as an adjunct to long-range AMTI, hyper spectral imaging (HSI) and three-dimensional (3-D) laser imaging. HSI is an emerging technology, says Crumbacher, suitable for counter-CC&D and chemical/biological sensing and targeting, while 3D laser imaging provides high-resolution information to support "intelligence preparation of the battlefield" and target recognition.

Communications are critical - requiring assured datalinks to theatre formations using laser communications and "up/cross-links" for reach-back to the USA. Kaehr says AFRL is experimenting with lasers as wideband datalinks. They "work well" for line-of-sight and in good weather, he says. Most datalinks will continue to be RF and the "race for bandwidth" will continue, he predicts.

Crumbacher says one challenge is affordability. The $50-100 million price of the RF suite must be reduced to $5-10 million. Also, AMTI performance needs around a 30dB improvement over today's systems while GMTI needs a 12dB enhancement. Technologies will need to be developed for: beamforming when the aperture is in a double-curved surface such as a wing; a 1000-times reduction in the size and weight of receivers; a weight reduction of at least100-1,000 times for the whole-system; and lightweight, compact and tuneable lasers. Sophisticated electronic protection techniques will also need integrating to harden the systems against advanced electronic warfare.

Conformal and integrated low- and high-frequency apertures are also a challenge. Kaehr says conformal RF-aperture experiments have been performed and the Sensors directorate is considering lighter emitters to help reduce the cooling requirement. He says emerging technologies make it possible to place the analogue-digital interface nearer to the aperture. The shorter this distance, the greater the opportunity for providing functionality through software rather than with more expensive, and more difficult to upgrade, hardware. It also improves the ability to beam-steer and change an aperture's function.

Kaehr says that ideally a single aperture will be used for all radar functionality, with software control determining which array elements operate. Electronically scanned active arrays are required to provide the flexibility and programmability of the elements. Also, the aperture could be used for communications - a directed output - while it could also act as a receive-only ESM sensor. "We're trying to provide focusing for different kinds of applications and considering how to adjust techniques to achieve this. We could go anywhere from here," says Kaehr.

Source: Flight International