SODAR

SODAR stands for " Sound / Sonic Detecting And Ranging " and is an acoustic remote sensing techniques.

In this measuring method audible sound pulses are bundled into the atmosphere (specifically atmospheric boundary layer) radiated. A portion of the acoustic energy is back-scattered by inhomogeneities which are caused by the thermo- dynamic structure of the atmosphere, and is received. Due to the Doppler effect of the backscattered acoustic signal can be determined from the measured duration, intensity again received and the frequency shift of the wind direction and wind speed at different heights calculated.

These remote sensing systems are mobile and usually operate continuously and automatically. They are used as a supplement to conventional wind measurement, which takes place near the ground. The devices can deliver data at a height of about 40 to 600 m above the ground with a vertical resolution of 20 m.

The devices will distinguish between two different types:

• Monostatic devices measure the backscattered sound. Transmitting and receiving antenna are identical. A transmitting and receiving unit is switched alternately between transmission and reception. Data can be collected from many elevation levels.
• In bistatic devices transmit and receive antennas are placed apart, usually at a distance of more than 50 m. In contrast to the mono- static type information can be collected only from a limited height layer.