The use of a FM CW radar for the measurement of atmospheric sound velocity profiles is investigated. In contrast to particulate scatterers or clear air turbulence the sound waves represent a coherent scattering structure, and the consequences are examined. We derive the theoretical shape of the signal spectrum and present examples of velocity profiles of vertically propagating sound waves. As the sound and clear air echoes are separable by frequency, simultaneous measurements of atmospheric wind and temperature profiles should be feasible. Because of the excellent spatial and temporal resolution of the FM CW technique, these measurements perhaps offer a possibility of future remote heat flux measurements.

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A high-frequency Doppler sodar for precipitation measurements has been developed. Such a Doppler sodar (6-20 kHz) can almost always measure precipitation and turbulence spectra simultaneously. Therefore, the mean vertical wind and spectral broadening effects can be directly removed. As the acoustic refractive indices for ice and liquid water are almost the same, the acoustic retrieval of precipitation can also be applied to rain with small hail (e.g., diameter D Ͻ 10 mm) or large hail, but for the latter, neglecting the effects of different orientations and shapes of hailstones.The authors' single-board minisodar is based on the digital signal processing (DSP) technique. The first prototype has been continuously operated at a coastal weather station since 25 October 2002. For stratiform rain events, the minisodar showed good agreement with a Joss-Waldvogel disdrometer and an optical rain gauge. However, for convective heavy showers, the minisodar always observed higher rain rates.The continuous, nonattended automatic operation of the minisodar has shown its capability for all kinds of precipitation measurements. The retrieval of precipitation rates for snow and graupel will be provided in a subsequent paper.

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To develop the theory of FM CW radio acoustic sounding system (RASS), in this paper an analysis of influences from temperature gradient and radial range decay is presented. A nonconstant temperature gradient will significantly modify the spectrum of scattered signals and also cause a deviation of the maximum position of amplitude spectrum from the Bragg resonance, which should involve using any retrieval algorithm that will correct for this temperature bias. Without considering this effect, the error of 0.5–1 K will probably be introduced in the RASS temperature profile. An approximate retrieval algorithm is provided in text. Moreover, for the application of RASS using FM CW radar in lowest 100‐ to 200‐m atmosphere, the far‐field aspect sometimes will not be the case, and radial range decay will play a certain role, which is investigated also in this paper.