Noise in coherent Doppler sonar velocity measurements: Where does it come from and what can you do about it?

Coherent Doppler sonars such as Doppler velocimeters can provide water velocity measurements with turbulence resolving accuracy in environments where other measurement systems struggle. Most notably in field settings where laser based instruments are often limited by turbidity and may be difficult to align and deploy acoustic instruments are a natural choice. For most applications, the high quality of coherent Doppler instruments provides data that requires little or no corrections to achieve sampling goals. However, there are applications where the instruments are pushed to the limits of their capabilities and on those occasions, it is essential to be aware of the various noise sources that limit their performance. This paper discusses the fundamental noise sources in coherent Doppler sonar and provides some examples on how to suppress the effects of that noise in velocity spectra.