Sonic Detection and Ranging (SODAR) is a ground based remote sensing technique for measuring wind speed in the three directions. It is based on Doppler shift in the frequency of the sound waves that are backscattered by temperature fluctuations in the atmosphere.
As the hub heights and blade lengths of turbines have increased, met-tower based measurements at 40, 50 and 60 meters, or sometimes 80 meters height are inadequate to provide an accurate estimate for wind speed at the hub height, let alone over the entire turbine rotor. With both hub heights and rotor diameter above 85m, met-towers of height 150m or more would be required to measure the wind speed over the entire turbine rotor. This would be cost prohibitive. SODAR provides an economical method to measure wind speed in this range of heights.
I have written a whitepaper that describes how SODAR may be cost effectively used for prospecting. With SODAR based measurements a developer is able to evaluate multiple sites in a short amount of time. For instance, over a period of 6 months, a developer may be able to evaluate 6 to 7 potential sites with real measurements at heights of 50 to 200 meters in increments of 10 meters. In most cases, short-term (4 weeks) SODAR measurements are sufficient for this task; it requires that the correlations with longer-term reference wind data be within acceptable range.
Article written by Dr. Pramod Jain
Email Pramod at pramod@frombeginningtowind.com
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