Notes on Multiple Frequency Operation of SODARs

In case that data availability in the upper height ranges must be increased a multiple frequency technique can be used. It is the experience that independent of the method (single or multiple frequency type) the most important parameters determining the height coverage are the atmospheric reflectivity (varies by a factor up to 1000), background noise (varies by a factor up to 100) and operational parameters.

There are some significant shortcomings in the multiple frequency technique:

• Increased acoustic band width, sodar is more sensitive to broad band noise
• In case of strong wind shear ambiguities within neighboured frequencies could occur

Benefits are:

• Increase of the signal/noise ratio by a factor of N^0.5, N = number of frequencies.