Beam swinging

From Glossary of Meteorology
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beam swinging

A technique used by wind profilers to determine the vertical profile of the wind vector above the radar by measuring the line-of-sight component of the wind sequentially along each of several different beam directions. The different beam directions can be obtained in various ways: 1) mechanically steering a single fixed-beam antenna; 2) electronically or mechanically steering the beam of a single fixed-position antenna (
see phased-array antenna); or 3) switching between multiple fixed-beam antennas.

Three beam positions can be used to determine the wind vector if it is assumed that the wind field is the same along those beams. At least five beam positions must be used to measure both the wind and its divergence. Wind profilers typically use one vertical beam and oblique beams that are between 10° and 25° off vertical. Oblique angles closer to the zenith make separation of horizontal and vertical wind components difficult and larger zenith angles make it less likely that the wind is uniform over the horizontal distances between beams. Large zenith angles also increase the radial range to the scattering volume at a given altitude, thereby reducing the strength of the returned signal.