SURFACE WINDSHEAR ALERT SYSTEM (SURFWAS) [1-3]

(Peter) H.-T. Liu

The Hazard of a Microburst

Microburst is an atmospheric phenomenon that creates hazardous low-level windshear.  Encountering a micro-burst by air-craft during takeoff and landing has caused numerous air traffic inci-dents/accidents (Fig. 1).  FAA has set high priority to improve low-level windshear related air traffic safety at airports.  Several airborne and ground-based windshear alert systems have been and/or are being developed.  The current ground-based system used by large airports are the Low-Level Windshear Alert System (LLWAS) which consists of a two-dimensional grid of wind sensors mounted on permanent towers.  The LLWAS is currently too costly for implementation at small airports.

Fig. 1. Scenarios of Microburst Encouter During Takeoff and Landing

The SURFWAS

A prototype SURFWAS was assembled and tested successfully at the U. S. Air Force Academy airfield during August 5-23, 1996 (Figs. 2-3). The SURFWAS was developed as a low-cost version of the LLWAS. The PC- and Windows-based SURFWAS consists of a linear array of 7 to 10 wind sonsors mounted on portable Remote Stations (RSs) erected along side the runways.  Microprocessor-based controllers acquire and preprocess the wind speeds and directions locally at the RSs and transmit that data via radio to the master station at the Air Traffic Control (ATC). LabVIEW programs were developed to (1) poll the wind data squentially from the RSs, (2) derive the runway-oriented windshear based on the measured wind data (Figs. 4-5), (3) display the wind conditions at the ATC tower (Fig. 6), and (4) broadcasts windshear messages at a VHF frequency (Fig. 2).  The display is updated every 2 seconds. 

Fig. 2.  Overall Layout of SURFWAS

a.-c. aircraft, d. solar panel, e. remote station, f. propeller anemometer & antenna, g. PC controller, h. air traffic control tower

Fig. 3.  Scenes at U. S. Air Force Academy Airfield

Fig. 4.  Time Series of Windshear

Fig. 5.  Profiles of Windshear

Fig. 6.  Display at Air Traffic Control Tower (Update Frequency: 2 Seconds)

For a detailed description of the SURFWAS, refer to [1, 2, and 3].

References

[1] Liu, H.-T., Golborne, C., Bun, Y., and Bartel, M. (1998) "A Surface Windshear Alert System(SURFWAS) - Prototype    

     Development," AIAA Journal of Aircraft, 35 (3), May-June, 422-428.

[2] Liu, H.-T. (1998) "A Surface Windshear Alert System (SURFWAS) - Field Test," AIAA Journal of Aircraft, 35 ( 3), 
     May-June, 429-436.

[3] Liu, H.-T. (1998) “Real-Time LabVIEW Application for Operating a Surface Windshear Alert System (SURFWAS),” 

NIWeek^TM 98 , Austin, Texas, August 25-27 (Received the Best Application Paper Award for Field and Maintenance   

     Category).

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^TM NIWEEK is a trademark of National Instruments

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