Vertical Velocity

Hi

I am using Vectrino ADV. I found that in the output dat. file there are two columns for z direction velocity.  Which one is the correct vertical velocity? Should I take the average of them?

I would appreciate that if some one can tell me what each column represents. For example : first column is time, second one  is ?, third one is U velocity, forth is V velocity ,....

Thanks

Amir

Hi Amir,

The Vectrino used the 4 receiver probe to measure independent vertical velocity quantities (Z1, Z2).  You can elect to average them together in an effort to further reduce noise in the signal.

You should check the "header" file (.hdr) which will provide all of the information for each column.

Best regards,

Eric SIegel

I have measured the velocity in the water tunnel in low turbulence condition but the average velocity for Z1 and Z2  have big difference. Z2 average velocity is almost twice the Z1 average velocity. It does not make sense that both of them are measuring the velocity in the same direction.

So what is your Idea about that?

Thanks

Amir

Do you have  a side-looking or a down-looking probe?

- Atle Lohrmann

Hi

We use down looking probe.

Sorry for the long wait - several of us were at the Nortek user seminar in China this week.

The two vertical components should not be different -- they should be very, very similar. If this is not the case, data from at least one of the beams are not good.  Could you post a small segment of the data or an image of the four velocities?

Best regards, Atle Lohrmann

Dear Atle

I hope you had good time in China. I have attached the watter tunnel testing results for w velocity from Z1 and Z2 and plot them together.

I hope it works for you and gives you a good image.

Sorry I forgot to put label for x axis. it is time (s).

Thanks

Amir

Hi, thank you for uploading the figure.

It looks to me like the two vertical components have about the same variability but that there is an offset.  One thing that could create this is a slight tilt in one direction (e.g., the pitch = 2 degrees, roll = 0).  A tilt would mean that the mean horizontal current couples into one or both of the vertical velocity estimates.

My suggestion is that you subtract the mean from each time series and then compare the two.  This should give you a handle on the standard deviation of the difference.

Best regards, Atle Lohrmann