Method of detecting and compensating for precipitation in sodar systems

A method of detecting precipitation with a sodar apparatus that transmits sound beams into the atmosphere, detects echoes returned from the atmosphere, from the echoes determines a Doppler-shifted spectrum comprising the relative strength of the echoes at various Doppler-shifted frequencies, and estimates wind speed and direction, the method comprising:

• a) automatically estimating the presence of precipitation based on the Doppler-shifted spectrum by automatically distinguishing a frequency or frequency range in the Doppler-shifted spectrum that is associated with wind velocity from a frequency or frequency range in the Doppler-shifted spectrum that is associated with precipitation, in which automatically distinguishing a frequency or frequency range in the Doppler-shifted spectrum that is associated with wind velocity from a frequency or frequency range in the Doppler-shifted spectrum that is associated with precipitation comprises:
• i) automatically identifying two distinct peaks in the Doppler shifted spectrum, one such peak being associated with rain velocity and the other being associated with wind velocity, in which identifying two distinct peaks comprises applying a curve fit to the averaged spectra where the curve fit is a higher order polynomial curve fit of the logarithm of the spectrum;
• ii) automatically determining the predominant frequency of each peak individually;
• and
• iii) automatically determining when the peaks are not sufficiently distinct to accurately estimate wind speed as a determination of reliability, where the spectra of a number of samples in an averaging period are used to make the wind speed estimate and the determination of reliability;
• b) using the estimated presence of precipitation to automatically improve the accuracy of the wind speed estimate made in the presence of the rain;
• c) automatically estimating the severity of rain based on the Doppler-shifted spectrum;
• and
• d) using the rain severity estimates to more accurately determine when the presence of rain has degraded the reliability of a wind estimate.