EVS Suppliers Working to Increase Performance

Representatives from EVS (enhanced vision system) suppliers, Max-Viz and CMC Electronics, discussed ways they are attempting to increase the performance and utility of their systems at the FAA's New Technology Workshop earlier this month.

Dr. Richard Kerr, who is vice president and chief technology officer at Max-Viz, said his company has developed a patented "multiple-fused" infrared camera, which uses different wavelengths to better separate a background scene from the important images of runway, taxiway and approach system lights.  LWIR (long-wave infrared) or MWIR (mid-wave infrared) sensors present a better picture of the overall scene, while a SWIR (short-wave infrared) and/or a visible light/NIR (near infrared sensor) works best for conventional airports lights.  Either can see strobe lights when properly implemented, Dr. Kerr said.

A "multiple fused" sensor system can be separately optimized to eliminate the dynamic-range conflict of a single-sensor system, so neither function compromises the other.  In other words, problems such as "blooming" can be eliminated without reducing the thermal sensitivity to see what needs to be seen.

Early EVS also had a problem when the thermal contrast between the sky and ground was very high, which caused the image of one or other to be "saturated", which resulted in jumpy image levels and an image washout during banking or pitch maneuvers.

The Max-Viz solution to this situation uses an advanced autogain/level control that separates the amplitude of original image (low freq ac-coupled) and optimizes the gain and level of high frequency images, and then recombines the two into a composite image.  This not only greatly expands the system's dynamic range and maximizes its detail under all conditions, but eliminates jumpiness and optimizes the image for newer LCD displays that have limited gray shades.

Possible Solution to LED Problem

In his presentation, Dr. Kerr noted that a visible light/NIR sensor can sense LED (light emitting diode) as well as conventional lighting.  LED lighting is becoming increasing popular with at least some airport managers because of its lower operating costs and other attributes.  But Marc Bouliane, who presented for CMC Electronics, said LED approach lights can be problematic because its wavelength is undetectable by his company's current EFVS (enhanced flight visibility system), if it is only in the visible spectrum.

To solve the problem, Dr. Kerr said Max-Viz will use a new architecture that fuses a third, avalanche-CCD (charge-coupled device) camera, or a "VisGaAs" camera that can "see" the lights through SWIR wavelengths.  For combined MWIR/SWIR cameras, Max-Viz would propose using SWIR laser diodes.

Dr. Kerr said Max-Viz is working with the Harvey Mudd College to follow-on to the FAA's "white LED-based light bar" prototype activity, and is pursuing capability with the FAA's ATO-W (technical operations services) Navigation Service on operational concepts, technology development, and capability growth path, to find ways to penetrate fog significantly - when necessary - beyond the ability of the human eye but still be useful in good visibility by overcoming background noise, and EVS system noise at night.

Runway Infrared Range (RIRR)

One major operational issue that remains for EFVS (enhanced flight visibility system) users is the U.S, FAR (Federal Air Regulations) requirement that approaches by commercial operators (Part 135, 125, and 121) can't be commenced if the RVR (runway visual range) is below minimums.  Since EFVS (which displays an EVS image on a head-up guidance system) now allows an operator to descend below category-one minimums, when the runway is visible with the aid of the image-creating sensor, how should this requirement apply?  In other words, if the EFVS operator has a high probability of successfully completing such an approach, why shouldn't he  be allowed to commence it?

To comply with the rule's intent, and still use the capability of EFVS, Max-Viz proposes to use a special transmissometer that can produce an "effective EFVS RVR" (editor's expression), by measuring the local LWIR/MWIR range, while applying Allard's law (a mathematical formula that defines the relationship between the intensity of a light, atmospheric conditions, and the amount of light received at any given distance) to include the thermal background scene plus, a standardized way of accounting for runway lighting.

MMW Imaging Radar

Since the advent of EVS as a pilot aid, there has been a debate as to whether IR or MMW (millimeter-wave) radar does the better job of doing what the pilot needs - being able to accurately and reliably discern essential images of the outside environment in all naturally occurring low-visibility conditions.

On the one hand, IR supporters point to its ability to present a detailed picture of outside features in three-dimensional forms; on the other hand, MMW supporters, underscore its ability to penetrate certain types of water-caused visibility obscurations that attenuate the radiation on which IR relies.

Some believe the problem with millimeter-wave radar, when used as an EVS sensor, is that its raw imagery is relatively crude - in other words, its presents a poor quality picture to the pilot that is two-dimensional.  But if it could be combined with IR, and enhance important features of interest, such as runways structures and hazards, it could be valuable as a way to "fuse" the best characteristics of each technology.  Dr Kerr said that this is probably best done upfront before the image conversion to a prospective display.

Integrated EVS/SVS

In order for a SVS (synthetic vision system) to be useful for low visibility instrument approaches, Kerr said it is critical that a way be found to verify the integrity of its database.

One way to accomplish this is through an integrated display where the pilot does the verification by referring to another independent and reliable source.  Another way is to verify SVS position information is by correlating it with an EVS image automatically.

Max-Viz has been working with Rockwell Collins on SE-Vision (synthetic-enhanced), which is an integration of these sensors in cooperation with the U.S. Air Force Research Laboratories at Wright-Patterson Air Force Base, Ohio.  Flight tests of the system have been conducted with an FAA B-727 at the agency's Hughes Technical Center in Atlantic City.  01-31-2007.

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