Whistling at High Frequencies in the Dark

Dean Sigler Sustainable Aviation 1 Comment

The same millimeter wave-length scanning that sees through your clothes at TSA’s very personal pre-flight inspections in airports could also provide a new type of heads-up display for pilots.  With an ability to distinguish power lines and other finely-resolved images in otherwise total visual blackouts, the technology could find a place in navigation, searches, and even private flying.  A few drawbacks stand in the way, however.

MMW portraits of would-be travelers as seen by airport TSA scanners

Extremely high frequency MMW devices sense objects at a range just below that of the lowest frequency infrared light.  The high frequency allows a high level of discrimination in imaging.

Used in automobiles for applications such as radar braking and adaptive cruise control, the potential for adapting such devices to weather flying is promising.  Used today in military helicopters, it is highly useful in places like Afghanistan, where blackouts of Biblical proportions darken mountain passes at incredibly high density altitudes.  Operation Eagle Claw, the 1979 rescue attempt of 400 American prisoners in Iran was stopped by the inability of human eyes and then-current technology to penetrate a desert sandstorm.

Military hardware, despite the need for adding lightness, as Ford designer Bill Stout advocated, is still too bulky and heavy for the civilian market or for LSA-sized craft we might fly.  Private pilots might not face the extreme hazards of towering dust storms, but a heavy fog or intense rainstorm can be just as dangerous for navigation.  Answers might come from the automobile industry.

Beyond passive safety systems, active safety systems play a major role in reducing traffic fatalities. Active safety systems include adaptive cruise control and collision warning systems with automatic steering and braking intervention.

Freescale's depiction of MMW automotive applications

Freescale, a supplier of MMW components to the automotive industry, explains their workings.  “In a collision warning system, a 77 GHz transmitter emits signals reflected from objects ahead, at the side and to the rear of the vehicle and are captured by multiple receivers integrated throughout the vehicle. The radar system can detect and track objects in the frequency domain triggering a driver warning of an imminent collision and initiate electronic stability control intervention.”

Their MMW radar can perform simultaneous long- and mid-range monitoring, a level of situational awareness many drivers cannot equal.

Others, such as Mercedes, Volvo, and Mitsubishi, have been loading up the vehicles with active devices meant to protect the driver and passengers, and many manufacturers offer backup radar to alert the driver or even stop the vehicle if a wayward object or toddler is present.

Mitsubishi lists the requirements for MMW devices if expressway driving is to be made safer.

“It must provide sufficient performance for detecting a forward vehicle at distances greater than 100 meters from the host vehicle.  In addition, millimeter-wave radar for automotive application must also satisfy the following requirements:

1. It must be capable of oscillating, amplifying, modulating and demodulating millimeter-wave signals stably.

2. It must be capable of radiating a millimeter-wave signal toward a target with a suitable level of power, beam width, number of beams and timing.

3. It must be capable of maintaining robust performance in the environment of the host vehicle temperature changes and vibrations.

4. Taking into account ease of installation on the host vehicle, it must be compact and lightweight.

In the automotive world, the actions generated by the radar’s perception do not have to be perceived by the driver.  The same may be true in an automated commuter aircraft.

Whether these radar images can be translated into images that make sense to a pilot is another matter, though.  Despite the acuity of the radar and its ability to control automated processes outside the view of the driver or pilot, a recognizable glass panel or heads-up display might be several steps away at the level needed for Dr. Seeley’s idea of safe commuter flight in and out of neighborhood pocket airports.

MMW, LWIR test vehicle - equipment probably too big for light aircraft use

2009 tests by QinetiQ and Boeing-SVS, Inc. showed that passive MMW had some limitations, and that combining MMW with long wave infrared and low light level television (LLLTV) might help make obstacles visible in otherwise brown-out conditions.  Despite MMW’s low resolution (four times less than LWIR) and 13 times less than visible light, it was able to distinguish power lines at a range of 160 meters (about 500 feet).  Researchers felt that improvements to the imager “could increase this by a factor of three.”

Their findings were reported in “Evaluation of a Passive Millimeter Wave (PMMW) imager for wire detection in degraded visual conditions, ” in the April 2009 journal of the aptly named SPIE – the international society for optics and photonics.

PMMW could distinguish power lines when the more high-resolution LWIR and LLLTV could not, indicating a higher contrast in its images.  Again, translating these fuzzy representations into useful displays might be a matter of computer processing that creates a useful human-radar interface.  This may not be necessary if the aircraft is fully automated, like Sebastian Thrun’s Google automobile, which has now travelled at least 140,000 miles without human intervention.

Comments 1

  1. Whistling at High Frequencies in the Dark

    by Dean Sigler on 06/10/2012

    What is done with the interference from the random emissions of other vehicles? It will get very noisy out there….

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