Basic Principles of Surface-Based Remote Sensing - Surface Based Remote Sensing of the Atmospheric Boundary Layer - page 42

Fig. 3.3 Micro Rain
RADAR (courtesy of
METEK GmbH, Germany)
3.3 SODAR
A SODAR is an active acoustic remote-sensing device that (nearly) vertically emits
sound pulses and receives and analyzes the backscattered part reflected from refrac-
tion index fluctuations in the atmosphere. The name of this device is formed in
analogy to RADAR and means sound detection and ranging (Gilman et al. 1946 ).
An overview of the basic principle of sounding with a SODAR and the history of
the development of this instrument is described in Peters ( 1991 ). SODARs analysing
the Doppler shift of the backscattered sound pulses for the derivation of the vertical
wind profile are called Doppler-SODARs.
Sound waves are scattered at turbulent density fluctuations in the atmosphere,
which are supposed to move with the mean wind, because the refraction index for
sound waves is changing at the boundaries of these fluctuations. For a monostatic
SODAR (the receiver is identical with the emitter), the intensity of the backscat-
tered signal depends only on these density fluctuations; for a bistatic SODAR
(the receiver is deployed away from the emitter) also velocity fluctuations in the
atmosphere contribute to the intensity of the backscattered signal. The density fluc-
tuations are mainly determined by temperature fluctuations. From a non-turbulent