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Written on: 2010-12-08, 16:25
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conorryan8@gmail.com
Conor Ryan
Topic creator
registered since: 18.09.2010
Posts: 6
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I have a lot of CTD data that I wish to calculate the mixed (surface) layer depth of..
How can I go about this?
Thanks,
Conor
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Written on: 2011-02-04, 14:03
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hecinho@gmx.de
Stephan Heckendorff
registered since: 24.04.2008
Posts: 279
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Hi Conor,
I am pretty sure that the mixed layer depth of a CTD profile cannot be calculated by ODV.
Alternatively, you can add a meta-variable for this information to your collection and manually input the approximate values from what you see in the data windows. I know this is not what you are looking for...
Cheers, Stephan
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Written on: 2011-02-07, 15:40
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hecinho@gmx.de
Stephan Heckendorff
registered since: 24.04.2008
Posts: 279
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Hi Conor,
I talked to Reiner Schlitzer and he suggests a way how to calculate the mixed layer depth in ODV.
First, we need 3 derived variables:
- Potential Density (Sigma-0)
- Vertical Derivative (of the previously defined potential density)
- Depth (from pressure)
The potential density indicates when the mixed layer ends. Down from the surface, density should remain (relatively) stable until the end of the mixed layer is reached. There is but one problem about density: the initial density value might differ greatly from station to station. All we want to know is WHEN does the value start to change. Therefore we add the derived variable vertical derivative of potential density.
Now, all that's left to do is to create the isosurface variable Depth @ Vertical derivative of potential density = <threshold>. This isosurface variable will hold the depth when the vertical derivative exceeds the threshold which should be the end (depth) of the mixed layer. As threshold I used 0.01 but I am not an expert so this might not be the best possible choice.
Afterwards the mixed layer depth can be visualized in a SURFACE window or exported to a spreadsheet file by choosing Export -> Isosurface variables from ODV's main menu.
Hope this helps.
Cheers, Stephan
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