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Marine Data Literacy 2.0

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Home > 4. Ocean Data View > 4.4 Section Plots

4.4 Creating Marine Data Section Plots in ODV

  • Exercise Title: Creating Marine Data Section Plots in Ocean Data View (ODV)

  • Abstract: The method to create section plots, and some basic gridding to improve the visualization, are presented.  The geometry of the section itself is saved in a special ODV "section" file, as well as the overall graphic in an ODV "view".

  • Preliminary Reading (in OceanTeacher, unless otherwise indicated):

  • Required Software:

  • Other Resources: 

    • ODV collection osd_all_liberia_wod.odv

  • Author:  Murray Brown

  • Version:  March 2012
1.  A section plot is a vertical "slice" through the ocean, along an alignment that is often -- but not necessarily -- a straight line, portraying the vertical structure of a selected property along the alignment.  
2.  You should see something like this in ODV, after the previous exercise.
2.  Selecte VIEW > LAYOUT TEMPLATE > 1 SECTION WINDOW
3.  This initial window appears, telling you that the "section" must be defined first.
4.  Right-click on the small station map, and select MANAGE SECTION > DEFINE SECTION
5. This new map of the stations appears.  You will "draw" the section spine on this map, with your cursor.
6.  Click your cursor at the point where you want to begin the section.  Then draw it over the map to where you want to end the section.

Double-click at the end point.
7.  This section properties window opens.  Enter a good title for the section.

Make sure SECTION COORDINATE = DISTANCE.
8.  Change BATHYMETRY from NO BATHYMETRY to FILE.

No choice appears in the FILE selection space.

Click on BROWSE to see your choices.
9.  Now you can see that the ETOPO2 plug-in bathymetry that we included during setup is available.  Select it, and click OPEN.

 
9B.  Change the MEAN WIDTH (of the section) to 100 km.

Then click OK.
10.  This figure appears.  It is almost a section, but not quite.

Right-click on the graphic and select X-VARIABLE.
11.  Select SECTION DISTANCE, then click OK.
12.  This is the section, where the variable is displayed as colored dots.  The color scale is on the right.
13.  To "fill in" the white space, we'll need to grid the data.

To begin this process, right-click on the graphic and select PROPERTIES.
14.  This 6-tab window appears, providing a huge number of options.  We don't have time to learn all of them now, but we can go through the tabs to see what they cover, generally.

For GENERAL, we can accept the choices.
15.  For DATA, reverse the X-AXIS , so the sense is the same as the original station map, by checking REVERSE RANGE.
16.  For DISPLAY STYLE, select VG GRIDDING. And uncheck DRAW MARKS so they don't show.

The X SCALE LENGTH is the effective distance, horizontally, that data points are used in the gridding, expressed as thousandths of the screen width.  Set it to 100, meaning 10% of the screen width.

Similarly, set the Y SCALE LENGTH (referring to the vertical range) to 50, or 5% of the screen width.

NOTE:  Scale lengths in the sea are always greater in the horizontal dimenson than the vertical.  Also, long-shore scale lengths (for gridding along that axis) are greater than shore-normal scale lengths (for gridding along that axis).

 
17.  For CONTOURS, you could set specific contour values to be displayed, with control of the line colors, types, etc.

We'll leave this alone for now.
18.  For COLOR MAPPING, you can take complete control of the palette, and you can set the mapping to be non-linear.  This would be good for variables such as chlorophyll, which have highly non-linear distributions skewed strongly toward zero.

We'll leave this alone for now.

And the DIVA tab is for an optional gridding package that we are not using now.  You can explore it later on your own, if you install it.

Click OK.
19.  This is the gridded section.  Notice that there are a few place where the data were so sparse that the algorithm just did not "fill in" the space.

Further increases to the X and Y scale factors could fix this problem, if you want a better graphic.

But notice that the label for the X axis is crowded by the station map along the bottom.  This doesn't look very good, so we need to edit the actual layout of the page.
20.  To do this, right-click on the graphic and select WINDOW LAYOUT.
21.  This brings up the "blue print" of the page, which can be edited.
22.  Right-click on the lower rectangle (the station map) and select MOVE/RESIZE.
23.  Drag the upper border fo the rectangle down a couple cells.

Then double-click inside the red frame to capture this new size.
24.  Righ-click anywhere on the layout, and select ACCEPT.
25.  This brings us back to the graphic, where our edit has fixed the problem.  This excellent section is suitable for publication.
26.  To save the physical settings for the section, right-click on the station map and selct MANAGE SECTION > SAVE SECTION AS
27.  Accept the location and filename extension ODV wants to use, and enter the name liberia_offshore_southwest.  You can always return to this section, with the LOAD SECTION control you see above in Panel 26.
28.  Also select VIEW > SAVE VIEW AS to save the entire graphic you see in Panel 25.  Accept the location and filename extension ODV wants to use, and enter the name liberia_offshore_southwest_section
29.  On your own:  Explore the properties controls for the section, and see if you can eliminate the white holes.  Also see if you can add labelled contour lines to the plot.
30.  On your own:  Right-click on the section and select other variables for display.  You may have to make property adjustments for variables where not many data points are available, but these are matters for you to discover.