Runway Windshear Detection Moves to the Next Level in Hong Kong

Hong Kong Int'l Airport (HKG) may be the first major airport in the world using an advanced form of radar technology to alert controllers and pilots to potentially dangerous windshears.

Although waves of new technology have greatly lessened the risk of flying into windshears on approaches or departures, the risk to aviation is still significant, partly because the detection systems most airports use are particularly good at detecting these hazards only at certain times -- like during a storm -- but not at others. Hong Kong's new system combines several types of technology, including Doppler Light Detection and Ranging (LIDAR) radar, to improve windshear detection and predictability.

The Hong Kong Observatory says its "LIDAR Windshear Alerting System" (LIWAS) has been in continuous operation since last December. LIWAS regularly scans the flight paths for both runways and provides up-to-the-minute warnings to departing and arriving aircraft. "It's the world's first operational system applying laser technology in airport windshear conditions," the observatory says.

"The operational use of the LIDAR together with a number of other windshear alerting methods developed by [the observatory] has significantly improved the hit rate of windshear at [Hong Kong Airport] from the previous 50 percent level, back in 2000, to the current 95 percent level," the observatory's senior scientific officer, Chi Ming Shun, tells Air Safety Week. "In fact, the windshear hit rate has been consistently above 90% in the past three years."

"The development of the windshear detection technique [for Hong Kong] is world-beating technology and places Hong Kong as a center of excellence within the aviation meteorological community," says Cptn. Brian Greeves, airport liaison facilitator and Asia Pacific coordinator for the International Federation of Airline Pilots' Associations (IFALPA). Greeves has been involved for many years with development of the system in Hong Kong.

In the United States, LIDAR remains in experimental use only at several airports, including San Francisco Int'l and Lambert Int'l (STL) in St. Louis, Mo., under the direction of the Massachusetts Institute of Technology, Greeves tells Air Safety Week.

Terminal Doppler Weather Radar (TDWR) systems, which are currently in use at many airports in the United States and worldwide, are already effective in detecting windshears and microbursts that occur during a storm. These systems bounce their microwave signals off fairly large particles -- such as raindrops (or even insects) -- that accompany and flow in the same patterns as the wind. But if it's a clear day, TDWR doesn't work as well. There's no large water particles for the signals to bounce off.

LIDAR, by contrast, uses laser light to bounce off much smaller particles (such as dust) that are commonly found in clear air. Between the two types of systems -- TDWR and LIDAR -- most of the conditions that produce windshears are covered. At Hong Kong, these two radar systems are combined with still other types of sensors, such as anemometers. All the data is interpreted by some newly updated algorithms developed by the observatory, which are not yet available outside Hong Kong, Greeves says. It's the integration of the new algorithms and all the different detecting equipment that gives LIWAS its high hit rate, whether or not there's any rain.

Anemometers, like TDWR, are also in common use at U.S. airports and others around the world. They're usually placed in sets of three at each runway (at either end and in the middle), to help detect wind speed and direction.

Hong Kong is an especially ideal location for LIDAR because of the surrounding terrain. In most cases, windshears are associated with rainstorms. But dangerous wind events of various kinds, including mountain waves and rotors (Air Safety Week, April 3) are also common next to mountains on their lee side (the side opposite the direction the wind is blowing from). Next to the airport in Hong Kong are several mountains rising to more than 3,000 ft.

Back in the late 1990s, researchers from the National Center for Atmospheric Research (NCAR) in Boulder, Colo., were investigating the potential for LIDAR-based runway windshear detection, and did a feasability study in Hong Kong for developing an "automated" system (one that generates automated alerts from taking continuous radar and sensor readings). But when NCAR first approached local officials about using LIDAR, they resisted, reports NCAR's Larry Cornman, who was deeply involved both with NCAR's LIDAR research and the initial Hong Kong study. At the time, that was a reasonable enough decision, Corman adds. That's because the technology was still very new and does not work as well as it does today.

NCAR's contract in Hong Kong ended before the new airport opened, and also before local officials changed their mind about LIDAR.

So the bottom line with TDWR is that it works very well when there's water droplets, and LIDAR shines when the sun does likewise and there's still plenty of dust. Because LIDAR works so well when the air is crowded with small particulates, the technology can be expected to work very well in a large city like Hong where there's a high level of pollution, Cornman tells Air Safety Week. By contast, in Juneau, Alaska, where NCAR conducted some of its LIDAR research, it was a very different situation. Like Hong Kong, the Alaskan capital presents some pretty tricky navigational problems because of its surrounding mountains. But the air is just too un-polluted (as of yet) to allow LIDAR to work very well.

Overall, rather than having one or the other type of technology, it's an ideal situation to have both TDWR and NCAR, as Hong Kong now has, Cornman adds.

Currently, the LIWAS hardware components deployed at Hong Kong Airport consist of the TDWR, the LIDAR, a number of anemometers and other sensors. There's also only one LIDAR device at the top of the air traffic control tower in between the two runways, which is not an ideal way to position the system, Greeves says. In a couple of years, a second LIDAR device will be installed at the north end of the airport.

>>Contact: Chi Ming Shun, Hong Kong Observatory, 852 2926 8435, cmshun@hko.gov.uk; Brian Greeves, IFALPA, 852 9456 9650, tasco@netvigator.com; Larry Cornman, NCAR, (303) 497-8439, cornman@ucar.edu

[Copyright 2006 Access Intelligence, LLC. All rights reserved.]

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