sound speed measurement

I have a question related with deployment settings, namely the sound speed measurement. After equiment retrieve, I have noticed that the the sound speed was selected as fixed. the equipment was deployed in ocean water and the user specification for sound speed was by default 1525 m/s (equipment default). Do you think that the user specification for sound speed can carry any problems in velocity measurements? How large can be the diference between both, measured and fixed sound speeds in relation to velocity?

Is there any solution for my already retrieved data?

thank you

Hi Ana,

Speed of sound corrections are fairly easy to accomplish. This actually just came up for a Vectrino user as well: http://www.nortek-as.com/en/knowledge-center/forum/velocimeters/138076447

There will be a bias error in the velocity measurements because of the fixed speed of sound, the magnitude will depend on how big the difference between the actual speed of sound and the fixed speed of sound is. If this is a profiler, there might be some bias in the measurement cell locations as well, but I'm not sure of the exact details on how those locations are calculated.

Solution is in the thread linked above, a very simple correction and your data should be fine.

P.J.

Hi Peter

Thanks for you reply.  I took a look into the formula

V_new = V_old * (c_new/c_old)

So I just need to correct the sound speed to have corrected velocity (V_new), correct? However, my concerns are in the velocity profile (velocity and pressure). If the sound speed is provided from temperature+salinity+pressure, and if I had assumed a fixed sound speed, these same factors are wrong?  How can I correct them? Is there any users manual with formulas description?

cheers

ana

Hi Ana,

You can use the calculator Øistein refers to in  Sound speed vs sound speed used to calculate the speed of sound. I suggest that you start out calculating some of the extreme values (in pressure and temperature) and see how large the error is. Maybe you will find that it is sufficient to apply the same correction for all the data. If you find that you need the full correction you must calculate the true speed of sound for each data point and apply the correction accordingly for each data point. Here is a link to the algorithm with a coding example.

Cheers,

Sven

Hi sven

Thanks for your reply!!!! I had already found the algorithm and applied to each data (true speed at each data point). At the moment I have my sound speed corrected. My question is if the recorded temperature, salinity and pressure at each data point are rigth?

cheers

Ana