Aquadopp noise levels

Hi. 

I had thought that noise  (e.g. vertical velocity precision) for Aquadopps was roughly proportional to 1/sqrt(averaging time) and 1/sqrt(range resolution), but it looks like it's actually roughly proportional to 1/sqrt(averaging time) and 1/(range resolution), which means that sampling at high range resolution and averaging rangebins latter is a dumb idea (e.g. averaging 4 adjacent 10cm bins would produce roughly twice the noise of simply recording with 40cm bins in the 1st place).  Sorry to ask such a basic question, but this is something I seem to have miss-understood, and I just wanted to quickly check before I put the instruments in the water (if correct, a yes would do.  I realize that there are some corrections because of triangular weighting etc - I'm not worried about these so long as they are fairly small)? 

Thanks very much

Steve H.

Hi Steve,

Yes, the velocity precision is proportional to 1/sqrt(number of pings) and 1/(range resolution). Note that I have replaced averaging time with number of pings as the measurement load will also come into account. But if you switch disable the auto setting on the measurement load your expression is correct. You can verify these relationships by changing the configuration parameters in our deployment software. The measurement load sets the number of pings per second.

Best regards,

Sven Nylund

The reason it is this way is because the range cell size is not only determined by the receive window (i.e. how long we listen) but also by the length of the transmit pulse,

Best regards, Atle Lohmann