Electromagnetic acoustic probe

From Glossary of Meteorology
Revision as of 16:56, 26 January 2012 by imported>Perlwikibot (Created page with " {{TermHeader}} {{TermSearch}} <div class="termentry"> <div class="term"> == electromagnetic acoustic probe == </div> <div class="definition"><div class="short_definiti...")
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)



electromagnetic acoustic probe

(Abbreviated EMAC probe.) A device tested in the late 1950s and 1960s that used acoustic waves to create clear-air targets for a continuous-wave radar.

The acoustic source produces sound waves that perturb the atmospheric refractive index. The perturbations propagate at the local speed of sound and serve as targets for the radar. When the acoustic wavelength is matched to half the radar wavelength, a resonance condition develops that leads to the production of a detectable radar echo (
see Bragg scattering). The Doppler shift of this radar echo is a function of the virtual temperature and the wind component along the direction of the radar beam. Radio acoustic sounding systems (RASS) also use this principle, but with a vertically pointed beam so that the Doppler shift depends on virtual temperature and the vertical wind component. The vertical wind component in RASS is removed either by time averaging or by making independent measurements of the wind. The EMAC probe was designed to make wind measurements with an operating range of 400 m. The virtual temperature (and corresponding speed of sound) was assumed, based on an independent measurement at the radar site.


Copyright 2022 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact permissions@ametsoc.org. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.