Creating Marine Data Section Plots in ODV OTGA – UEM TRAINING COURSE – FUNDAMENTALS OF OCEACOGRAPHIC DATA MANAGEMENT , 23-27 JANUARY 2017, MAPUTO, MOZAMBIQUE Prepared by: Harrison Ong’anda, National Coordinator, Kenya National Oceanographic Data Center (KeNODC) honganda@kmfri.co.ke, hochieng2003@gmail.com

A surface plot is not necessarily a graphic portraying any variable at the surface of the sea, although it can be. Surface plots portray any variable as it would be found on a 3-dimensional sheet within (or on, or just beneath) the sea, defined by a constant value of some other variable. For example, consider a sheet defining a temperature of 15˚ C within the sea; globally this sheet would be quite deep near the equator, but would rise toward (and even intersect) the the surface near the poles. A related surface plot could be, for example, the salinity found at all locations on this 15˚ degree sheet, specified as "Salinity at Temperature = 15˚ C". This type of plot became known and widely used when it was early discovered that mixing in the sea tends to occur along "iso-density surfaces" or sheets of constant density. Starting with density surfaces, such plots are now created and interpreted for many other variables.

Open the ODV collection (now this is farmiliar) Select VIEW > LAYOUT TEMPLATES > 1 SURFACE WINDOW

This graphic usually appears, the default plot in ODV for the surface mode.  Don't worry if your ODV shows something else.  We're only setting up now.

Now we're going to narrow down the data to just one season (January- February-March). Right-click on the small station map, and select STATION SELECTION CRITERIA.

For SEASON, use the drop- down menus to select FROM JAN and TO MAR.  This range is annotated as JFM below. Then click OK.

That takes care of temporal selections That takes care of temporal selections.  Now we need to worry about data quality and depths. Right-click on the data figure and select SAMPLE SELECTION CRITERIA. 

Here you have two tabs. Select the QUALITY tab. Select 0: ACCEPTED VALUE (meaning good) CHECK the box by APPLY THESE CRITERIA GLOBALLY Click APPLY TO ALL VARIABLE Then click OK.

We need to see what variables are available now.  To do this, select VIEW > ISOSURFACE VARIABLES.

This window opens, showing 4 default variables, none of which are needed by us. NOTE:  "First" in the ODV syntax means the shallowest sample at the station, not the sea surface.  "Last" means the deepest sample at the station, not the sea floor. Select all of the "FIRST" isosurface variables and use DELETE to remove them.  They are not needed.

Set the top line to read TEMPERATURE AT DEPTH [m] = 0 Set the top line to read TEMPERATURE AT DEPTH [m] = 0.  Then click ADD to complete the addition. Also add these other TEMPERATURE @ depths: 1000 m 2000 m 3000 m 4000 m 5000 m Then click OK when finished.

Now, let's view the new surface variables we created.   Right-click on the graphic and select the Z VARIABLE.

Then select TEMPERATURE @ DEPTH = 0. NOTE:  Yes, this was already chosen, but you need to know how to make these choices later on. Then click OK.

This graphic appears, showing (by color) the 0-m temperatures. NOTE:  There are some temperatures which you should not see if you chose only ACCEPTED = GOOD quality values.  If your value range goes up to 80, then go back and start over

We need to grid the data in ODV, for better viewing, so right-click on the graphic and select PROPERTIES.

Make these selections to get a good first gridding: Uncheck ORIGINAL DATA Check GRIDDED FIELD Select DIVA GRIDDING from the list of gridding methods Uncheck AUTOMATIC SCALE LENGTHS Set the X and Y scale-lengths to at least 100 (=10% of the map width).  This is a good first guess, but might need later adjustment Check HIDE BAD ESTIMATES QUALITY LIMIT set to 2.5 standard deviations (from the mean) Check DO COLOR SHADING Check EXCLUDE OUTLIERS Uncheck DRAW MARKS. Then click OK. Expect to wait a few minutes, in most cases, due to the more thorough gridding with this method. 

This graphic appears.  NOTE:  The image is rather boring, because the data range (which you can play with) is rather too large. Select VIEW > SAVE VIEW AS and save this view as temp_0m_jfm_moz_wod

Right-click on the small station map, and use STATION SELECTION CRITERIA to show only the data for July, August and September. After a few minutes, this image appears.

Set the Z for the 1000, 2000, 3000-m temperature (JFM).  etc

Finaly !!! Create Isotherm-Depth Ocean Front Climatologies in ODV by following the exercise at: http://marinedataliteracy.org/odv/depth_t.htm