SODAR
SODAR stands for " So und / So nic D etecting A nd R anging" and is an acoustic remote measurement method.
With this measuring method, audible sound impulses are bundled and radiated into the atmosphere (more precisely the atmospheric boundary layer ). Part of the sound energy is scattered back and received again through inhomogeneities that are caused by the thermodynamic structure of the atmosphere. The wind direction and wind speed at different heights can be calculated from the measured transit time , the received intensity and the frequency shift caused by the Doppler effect of the backscattered sound signal .
These remote sensing systems are usually mobile and work continuously and automatically. They are used as a supplement to conventional wind measurements, which are carried out close to the ground. The devices can deliver data over a height of approx. 40 to 600 m above the ground with a vertical resolution of 20 m.
A distinction is made between two different types of devices:
- Monostatic devices measure the backscattered sound. The transmitting and receiving antennas are identical. A sending and receiving unit is used to switch between sending and receiving. Data can be collected from many different altitudes.
- In the case of bistatic devices , the transmitting and receiving antennas are set up spatially separated, usually at a distance of more than 50 m. In contrast to the monostatic type, data can only be acquired from a limited height layer.