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September 2007

A smoother ride

RAL scientists test new system for alerting pilots to turbulence

John Williams

John Williams.

Turbulence is a fairly routine part of air travel, and usually the worst thing that happens is a little spilled coffee.

According to the numbers, however, bumpy rides are indeed a major danger to pilots and passengers, causing accidents, injuries, and deaths. Data from the National Transportation Safety Board show that turbulence was a factor in at least 509 accidents in the United States from 1992 to 2001, including 251 fatalities (mostly in the general aviation sector), and it is estimated that there are more than 1,000 minor turbulence-related injuries on commercial aircraft annually. The airline industry loses millions of dollars every year from injury claims, delays, extra fuel costs, and aircraft damage and inspections related to turbulence.

Since July, NCAR scientists have been collaborating with United Airlines pilots to test a new turbulence detection system designed in RAL. In this short time, the system has already proven itself successful at alerting pilots to patches of rough air they may encounter flying through clouds.

"We hope this capability will provide a significant boost to the aviation industry in terms of passenger comfort, safety, and reduced costs," says RAL's John Williams, project lead.

The new system centers on the NEXRAD Turbulence Detection Algorithm (NTDA), a computational procedure for processing radar data. John and colleagues designed the NTDA to analyze data from the National Weather Service's network of Doppler radars known as NEXRADs (Next-Generation Radars). The NTDA captures the intensity of in-cloud turbulence by analyzing the distribution of winds within a volume of the atmosphere measured by a radar pulse.

The system merges data from multiple radars and transmits a real-time snapshot of turbulence directly to pilots in the cockpit. In addition, a three-dimensional mosaic is made available to airline meteorologists and dispatchers via a Web-based display.

"Our goal is to use these radar measurements to create a three-dimensional map of in-cloud turbulence across the country that can help pilots avoid hazardous areas, or at least give them enough warning to turn on the ‘fasten seat belt' sign," John says.

Pinpointing turbulence in clouds is a challenging scientific problem. Turbulent areas may be small, evolve quickly, and occur outside the most intense parts of a storm. Because pilots have traditionally lacked accurate measurements of turbulence that develops in clouds, Federal Aviation Administration (FAA) guidelines suggest that planes avoid thunderstorms by at least 20 miles when possible, even though large sections of these airspaces may contain relatively smooth air.

When pilots fly through clouds, they lack an adequate system alerting them to specific regions of turbulence ahead. They may use onboard radars to avoid areas of heavy precipitation, but precipitation does not always correlate with turbulence. In the future, airborne windshear radars may be used to routinely measure in-cloud turbulence, complementing the broad coverage and storm-penetrating power of the NEXRADs.

Previously, meteorologists weren't able to reliably pinpoint turbulence from operational ground-based radars because of factors that can contaminate measurements, such as sunlight, ground echoes, nearby storms, and even swarms of insects. The NTDA uses quality control procedures to identify and minimize the impact of compromised data, while also averaging a series of measurements to improve the reliability of turbulence estimates.

This year's real-time NTDA tests build on smaller-scale demonstrations with United Airlines in the summers of 2005 and 2006. An analysis of NTDA data output compared to turbulence reports from United Airlines aircraft showed it was possible to successfully detect moderate or greater turbulence in clouds more than 80% of the time. Since then, the RAL team has refined the algorithm, and expects this year's results to show increased accuracy.

The uplink system is being tested through October by a group of United Airlines pilots who fly routes east of the Rockies. The pilots have reported that it is providing them with accurate, valuable information about turbulence that is not available from any other source.

The next step for the demonstration may be to expand the system to additional United Airlines aircraft as well as to other airlines. In addition, RAL recently delivered the NTDA software to the NWS Radar Operations Center for use on all NEXRADs. When the software is operationally deployed next summer, in-cloud turbulence information will be available to a variety of users.

The research behind the NTDA was initiated by Larry Cornman (RAL) more than 10 years ago. Other RAL staffers who have worked on the project include Gary Blackburn, Steve Carson, Jason Craig, and Jaimi Yee, as well as Andy Cotter, a former graduate research assistant. Shelly Knight, Greg Meymaris, and Bob Sharman also lent their support.

The NTDA is just one aspect of RAL's current turbulence work. Another FAA-funded project, led by Bob, is aimed at improving the Grapical Turbulence Guidance (GTG) system. The system, developed by RAL, currently runs operationally at the NWS Aviation Weather Center, providing 1-to-12-hour forecasts of upper-level clear-air turbulence intensity over the continental United States. Bob is working to extend the GTG forecasts to include mountain-wave turbulence and cover lower levels.

Larry is continuing an effort to equip commercial aircraft from several airlines with an automated turbulence reporting software system. In addition to his work on the NTDA, John is spearheading the development of a system to provide probabilistic predictions of turbulence in and around thunderstorms. The RAL team is also developing a system that will merge all these components into a single GTG product covering all sources of turbulence.

Other turbulence research activities include a NASA-funded feasibility study regarding the use of airborne passive infrared sensors to detect turbulence, an Air Force initiative to develop a mountain wave diagnostic for the stratosphere, and an investigation supported by Boeing into the ability of airborne GPS receivers to detect turbulence.

Doppler diagram

How it works: A network of National Weather Service Doppler radars known as NEXRADs transmit data to NCAR, where software analyzes the information and extracts the intensity of a stormís turbulence. The system then transmits a real-time snapshot of that turbulence directly to pilots in the cockpit, and makes it available to airline meteorologists and dispatchers via a Web-based display. (Image by Cindy Halley-Gotway and Lara Ziady, RAL.)

On the Web

More about the NTDA

In this issue...

A smoother ride

HAO's Phil Judge returns full-time after cancer

More power for the TeraGrid

Summer school—but not the remedial kind

Planning for retirement

SOARS poster session

Symposium salutes Warren Washington

Art + Science: EcoArts returns to Boulder area

UCAR ranks high in Colorado's Best Companies contest

Just One Look


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