Acoustic Sounding of the Lower Atmosphere

  • C. Gordon Little
Chapter
Part of the Meteorological Monographs book series (METEOR, volume 11)

Abstract

The refractive index of air to sound waves is a function of the three primary meteorological parameters of the lower atmosphere, i.e., wind, temperature and humidity. It is therefore of interest to consider to what extent the propagation of sound waves can be used to derive quantitative information on these atmospheric parameters.

It is shown that the fluctuations in acoustic refractive index may be expected to be about one thousand times stronger than in the radio case; hence, the scatter of acoustic waves may be expected to be roughly one million times stronger than for radio waves. In addition, the million-fold ratio between the velocities of electromagnetic and acoustic waves results in an acoustic system requiring one million times less bandwidth to interrogate a given atmospheric volume. This results in an overall reduction in interfering noise power for the acoustic case of about a factor of one million. For a single pulse, the acoustic signal-to-noise ratio from a given scattering region is likely to be some twelve orders of magnitude stronger than in the radio case.

The system parameters required to achieve an effective acoustic sounder are discussed. It is concluded that the acoustic sounding technique could be developed to monitor (to heights of at least 1500 m) the vertical profile of wind speed and direction, the vertical profile of humidity, the location and intensity of temperature inversions, the three-dimensional spectrum of mechanical turbulence, and the three-dimensional spectrum of temperature inhomogeneity (i.e., of optical refractive index fluctuation).

Typical time and height resolutions for the proposed acoustic echo-sounders could be of the order of 10 sec and 10 m; the spatial wavenumber explored could range from about 0.01 to ~400 m−1.

Limitations to the acoustic technique include its limited range (to perhaps 10 km) and the probability of serious loss of sensitivity due to increased noise level during periods of strong wind, hail or rain. Other difficulties include the low information rate [of the order 1 pulse (10 sec)−1] and the strong refraction effects due to wind and temperature gradients.

Keywords

Acoustic Wave Phase Velocity Doppler Radar Amplitude Scintillation Sound Scattering 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
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Copyright information

© American Meteorological Society 1970

Authors and Affiliations

  • C. Gordon Little
    • 1
  1. 1.ESSA Research LaboratoriesBoulderUSA

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