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A better resolution

Nav Canada’s next-generation AWOS.


September 15, 2008
By Ken Pole

Topics
dig_wx_cam
 Digital weather cameras will be installed at new sites and will replace existing analog cameras, providing superior image quality. WxCam images are accessible at www.flightplanning.navcanada.ca.

With the possible exception of meteorologists, few in the world fret more about the weather than pilots. They talk about it lovingly or with loathing, depending on whether flight plans get them around the weather or force them to fly through it. A measure of interest is the fact that Nav Canada’s aviation weather website, which has been significantly upgraded in the 10 years the corporation has been running air navigation services in Canada, averages at least 27,000 visits a day.

As manager of Aviation Weather Services at Nav Canada, John Foottit is particularly attuned to the flying community’s meteorological needs, whether in the cockpit, the control tower or elsewhere. His current challenge is replacing a “legacy” Automated Weather Observation System (AWOS) which has been around since the 1980s and used 1970s technologies.

Several years ago, Environment Canada’s weather wizards, under contract to Nav Canada, gave notice that data from the legacy system could not be guaranteed beyond May 2007. The warning was premature because there were enough spare parts to keep the system viable a while longer, but subsequent difficulty in getting some chipsets for critical sensors made it clear that time was running out.

There also was Transport Canada’s March 2005 exemption to Canadian Air Regulation 804 which, among other things, sets AWOS sensor accuracy standards. “Our legacy AWOS couldn’t meet those standards and couldn’t be modified,” Foottit said during a joint interview with William Estrada, manager of Flight Information Services Automation.
So Nav Canada solicited private-sector interest in the next-generation AWOS, yielding responses in the “double digits” from industry, where there was access to an array of potential off-the-shelf solutions. Companies with proven technologies were short-listed, leading to a request for proposals and an eventual contract with Coastal Environmental Systems of Seattle.

Estrada explained that Nav Canada has enhanced the AWOS. The legacy system, for example, does not report thunderstorm activity. The new AWOS will, using data provided from the nationwide array of sensors in Environment Canada’s Canadian Lightning Detection Network (CLDN). The AWOS wind sensor is also less vulnerable to weather in that it uses heated probes with no moving parts, so freezing rain or fog or wet snow doesn’t impair the data flow.

 laser_ceilometer
 The new AWOS will include the latest in Laser Ceilometer technology and report cloud bases up to 25,000'.

Foottit said the CLDN, using purpose-built lightning sensors, will triangulate a strike with high temporal and spatial resolution, reporting the data to users within 90 seconds. “The current system has an accuracy of plus or minus 500 metres of the actual strike.” All AWOS reports of thunderstorm activity originate with the CLDN.

“If there is lightning within five miles of its airport, the AWOS will report a thunderstorm there. If the lighting is within the five-to-10-mile range, it reports ‘lightning in the vicinity’ and if it’s further out, between 20 to 30 miles, the AWOS would report ‘distant lightning’ with the octant (within a 45-degree arc). In other words, it will be better than human observation for the distant lightning.”

Estrada said air traffic controllers and flight service specialists will receive a continuous data flow and, for pilots, any time there is a change, there is a virtually immediate update on the voice generator broadcast. It should be as close to real-time reporting as current technology can make it.

St. John’s and Iqaluit were chosen for the first tests because of their often extreme conditions, the idea being that if the new AWOS worked there, it would work anywhere. Nav Canada worked with air traffic management engineering specialists and the Meteorological Service of Canada on setting up new AWOS at each station as well as weather instruments for two regular observers. Four seasons of testing yielded 300 days of comparative data which were then analyzed by an independent engineering company, Digilog, which has extensive Canadian and U.S. expertise. The AWOS met Transport’s requirements.

“The biggest advantage is that the AWOS is very attentive in sampling the atmosphere and putting out a report every minute,” Foottit said. “So, 24 hours a day, seven days a week, you’re getting weather observation data.  That’s important to air crews, even if during the night when maybe there’s no traffic at a particular site. It gives you that continuum of what’s happening with the atmosphere.” It also makes it much easier for pilots to check temperature and humidity trends.

“We know from the testing that the accuracy of the data is good,” he said. “It’s not perfect, but then neither is a human being.” He cited U.S. trials involving human observers on opposite sides of an airfield. “You’d be surprised at the disparity between what those observers saw.” A pilot himself, he has had issues at St. John’s and Toronto Island Airport when ground observers were reporting situations which turned out to be quite different from what he saw himself. He landed in St. John’s because the conditions were not as bad as expected, but opted to divert to Toronto International when conditions at the island airport were poorer than had been expected. These examples highlight the fact that what the pilot sees from the cockpit and what is observed from the ground often differ in poor weather.

The new AWOS also relies on digital cameras rather than their analog forerunners at about 20 sites across the country. Estrada said resolution is significantly better, enabling operators to do a visual confirmation of the raw AWOS data. In addition to installations at all AWOS sites, cameras are planned for some 70 other sites where there currently is no weather data collection. Foottit said cameras will be particularly helpful where challenging terrain or some other site-specific situation is involved. “So if you call a Flight Information Centre, the specialist can access the imagery and give you a general picture of what’s happening, even en route.”
The new system will involve about 350 cameras at about 130 sites – with two cameras at
most and three at some – where approaches present unique challenges. All images are date- and time-stamped at 10-minute intervals so users can run through a sequence to see how a situation may be changing even as they’re on approach.

While most installations are expected to be relatively straightforward, Nav Canada is looking at a couple of Rocky Mountain sites which likely will require independent power sources and wireless communications. “If you’ve got some guy trying to take a Cessna 152 through the Rockies, the weather in Calgary and the weather in Kelowna may be great, but what’s in between?” Foottit asked. “You really want to have a close look at what’s going on.” Cameras are scheduled for installation wherever there is sufficient VFR traffic volume and, currently, no weather information. “If you weighted it across the country, we’re going to have far more in B.C. than we have in other places, but the cameras will be pretty much everywhere.”

Better lightning detection and virtually current imaging are only part of the equation. There has been a lot of “under-the-hood stuff” from an engineering and technical perspective, all designed to improve reliability and reduce downtime. “Do the math,” Foottit urged. “The legacy AWOS have three-month maintenance cycles; somebody has to go in and do things that keep it running. The new AWOS is annual.” Remote monitoring of the digital network also facilitates maintenance, giving Nav Canada technicians more of a heads-up about evolving issues. “That’s kind of on the boring side, but it does mean a lot to the customer,” Foottit said.

Foottit noted “one other small improvement” which could be a significant benefit for VFR pilots: air density data. “If you’re operating from an airfield that’s hot and high, it will do a density-altitude calculation and … you’ll get a much better idea of the performance you can expect from the aircraft.”

The first installation is already going in at Kelowna, simply because the weather breaks earlier in the Okanagan Valley. It is scheduled to be commissioned in September along with a couple of smaller sites in the West, all relatively close together to make best use of the specialized construction crew. It will take at least four years to complete all of the new installations because there almost always are issues to be addressed such as current use of a proposed site, legal and zoning issues, anemometer tower proximity to the runway, possible IFR approach limitations, etc.

While much of the hardware is off the shelf, some of the underpinning software and other elements are proprietary to Nav Canada, having been customized to address specific needs. “It’s expensive, but it’s the right way to do it, not just to meet Transport Canada’s requirements, but to meet our clients’ requirements,” Foottit said. “Aircraft operators have to rely on this; they have to trust it.”