P4.8 Use of a commercial wind sodar for measuring wake vortices

Tuesday, 5 October 2004
Stephen Mackey, Volpe National Transportation Systems Center, Cambridge, MA; and D. C. Burnham and K. H. Underwood

Sodars have unique capabilities for measuring aircraft wake vortices near the ground (vertical profile of the vertical wind component) and were used extensively for wake studies from 1975 through 1991, These utilized multiple sodars (at 8-10 locations) developed specifically for this single purpose. Sodars are particularly well-suited for tracking wake vortices between parallel runways.

Recent wake measurement campaigns have emphasized other wake sensors (lidars and windlines) but have often included minisodars to provide wind profiles up to 200 m above the ground. Detailed examination of unaveraged wind sodar data showed that wake vortex signatures can be detected in the vertical beam wind profile. In wind-profile mode the sodar gives a vertical wind profile only every 4 seconds. A vortex-only mode can be used which achieves profile updates faster than one per second by (a) using only the vertical beam and (b) reducing the maximum range.

Adapting a commercial wind sodar for wake measurements has a number of advantages over earlier technology and is more cost effective than recreating and updating the capabilities of the earlier sodars: 1. Phased-array antennas operate at higher frequencies and have less ringing. 2. A modern data acquisition system includes Doppler processing and records raw spectra and spectral moments. 3. The sodar units operate independently and require only power and digital signal connections. 4. Current deployment strategy uses a small number (e.g., 3) of sodars in conjunction with other wake sensors to (a) validate the measurements from the other sensors and (b) to provide high quality, consistent measurements at critical locations on an airfield.

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