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Marine Data Literacy 2.0

Providing instruction for managing, converting, analyzing and displaying oceanographic station data, marine meteorological data, GIS-compatible marine and coastal data or model simulations, and mapped remote sensing imagery





Home > 4. Ocean Data View > 4.8 Data Subsets

4.8 Exporting Marine Data from ODV: Data Subsets

  • Exercise Title:  Exporting Marine Data from Ocean Data View (ODV):  Data Subsets

  • Abstract:  Although most of our marine station data analyses will be performed in Ocean Data View, we need robust methods to export desired data subsets for work in other software.  In this exercise, you'll learn how data can be exported as ASCII TXT files compatible with most analysis-and-display software (e.g. Surfer, Saga and other GIS's).  The data exports will parallel the choices made in the Surface Plots exercise, i.e. 0-m and 4000-m products.

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

  • Required Software:

  • Other Resources: 

  • Author:  Murray Brown

  • Version:  11-5-2014

1.  Open the collection listed above.  Load any one of the views, but if you have it, then a TS Plot would be good to begin with.  Here's a TS Plot with oxygen as the Z variable.

Make sure that all filters (i.e. selection criteria) are relaxed so that you are viewing all the data points.

2.  Let's begin to prepare a data subset by right-clicking on the small station map, and selecting STATION SELECTION CRITERIA.
3.  Select the DATE/TIME tab and use the SEASON section of the page to select only the months of January through March (all days).
4.  Click OK and you will return to the scatter plot.
5.  Now right-click on the analysis map and select SAMPLE SELECTION CRITERIA.
6.  Click the QUALITY tab. 
  • Select 0 = ACCEPTED VALUE for all the data. 

Then click OK.


7.  Select the RANGE tab. 
  • Select the DEPTH variable, and set the ACCEPTABLE RANGE to 0 to 5 m.  This ranges from the shallowest standard depth (0 m) halfway down to the next standard depth (10 m).  So we could call this a "0-m dataset".

Then click OK.

8.  Here are all the "0-m data" for the months of Jan, Feb and Mar.  We could, for example, export these data for use in another program, or perhaps to send to a colleague.
10.  Navigate to PRODUCTS > ODV > SUBSETS and enter the filename data_from_osd_jfm_0m_5m_liberia_wod.txt.  (Notice that ODV helps with part of the filename.)
11.  In this window (which appears next), you can select the parameters you want to export in this subset.  DEPTH must always be included. 

You can select any or all of the variables for the export, but here we select all of them for simplicity.

Then click OK.

12.  ODV now wants directions from you on how to export the data:
  • Missing String Value:  Use the standard Saga "no data" value  -99999
  • Longitude Range:  Always -180 to + 180 for GIS-related work
  • Metadata Date Format: Select the ISO standard, as shown here
  • Data Filter:  Apply current settings
  • Use Compact Output Format:  Do not use (incompatible with other software)
  • Export Data Quality Flags:  Usually not needed.
  • Export Metadata Quality Flags:  Usually not needed
  • Export Data Infos:  Usually not needed
  • Export History: Usually not needed

Set these values, then click OK.

13.  NOTE:  Most recent versions of ODV require you to repeat the station selection criteria again.  These redundant steps are not shown here.
14.  WHY MAKE THE CHOICES ABOVE?  The best way to manage WOD data, for subsetting by time, space, source, etc. is in ODV.  Saga can do a little part of this, but not easily.  So we take all variables in this file.  But keep a master copy of this TEXT export for Saga work, because you may make changes in one variable that affect others.
15.  This message indicates the export was successful.  Notice that this is a very large amount of data.
16.  Now repeat the sample selection process, to specify a 4000-m data product (from 3500 to 4500 m)

This ranges from halfway between 3000 m and 4000 m down to halfway between 4000 m and 5000 m.  So this could be called a "4000 m dataset".

17.  Here's the TS diagram for the 4000-m dataset for the months of Jan-Feb-Mar.
18.  In the same way as above, export these data tables:
  • data_from_osd_jas_0m_5m_liberia_wod_odv.txt
  • data_from_osd_jfm_3500m_4500m_liberia_wod_odv.txt
  • data_from_osd_jas_3500m_4500m_liberia_wod_odv.txt

Now you have both depths for both seasons.  (2 seasons X 2 depths = 4 files)

19.  Take the time to inspect any one of the exported text files in any good ASCII editor.  Notice the 10 lines of header at the beginning (a relatively new feature of ODV).


20.  Using the STATION SELECTION CRITERIA and the SAMPLE SELECTION CRITERIA, you can create data subsets according to any spatial or temporal data needs, for your own work or as requested by colleagues.  Make sure the exported products are well-named (as above) so no mistakes are made about their origin or contents.
21.  Relax all criteria in the STATION SELECTION and SAMPLE SELECTION windows, after subsetting, so that you return to the use of all the data.