3.1 WOD Data
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3.1 Managing/Repatriating Area-Specific Marine Data from the World Ocean Database

  • Exercise Title:  Managing/Repatriating Area-Specific Data Collection from the World Ocean Database

  • Abstract:  The international collection of marine datasets, collectively named the World Ocean Database (WOD), is accessed, and several principal data types are downloaded (ocean station data, CTD data, mechanical bathythermograph data and expendable bathythermograph data) from the 11 available types.  These data cover the entire historical period of record, and an area slightly larger than the project area for Liberia, and will be used in subsequent exercises with the Ocean Data View software. 

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

  • Required Software:

    • N/A

  • Other Resources: 

  • Author:  Murray Brown

  • Version:  2015-02-18

1.  Open the WODSelect interface.  This is the interface to select the various optional ways the global data can be selected.

For this exercise, check GEOGRAPHIC COORDINATES, and DATASET; if you have any special interests in how the data are selected, then you can add other items, now or in a later run.

The OBSERVATION DATES item can also be checked, as discussed in a panel below.

2.  Near the bottom of the list of criteria are two new items we need to think about:
  • DATA EXCLUSION USING WOD QUALITY CONTROL FLAGS.  We recommend that you do not use this criterion now, because you can also do it later in Ocean Data View. 
  • DATA ADDITIONS.  "If you select this option you can include only new data added between given dates. This could be useful for someone who already has a collection and wants to update." [Greg Reed]  We recommend that you do not use this criterion until you have become much more familiar with ODV and have perhaps made some experiments to see how this filter really works.
3.  Now click BUILD A QUERY
4.  WODSelect has created a query form based on GEOGRAPHIC COORDINATES and DATASET type (the fields you selected above).

In the GEOGRAPHIC section, enter coordinates that are 1 degree larger than the area-of-interest polygon.  This gives you a margin of data around the Liberia area to avoid "edge effects" in calculations

5.  In the dataset section, check these items (or more, or fewer...up to you).  Then click GET AN INVENTORY.

6.  This inventory appears, indicating that nearly 17,000 station are available (for OSD). 
  • If you get (below) an inventory that would be too large for you, based on local Internet conditions, then go back and use the OBSERVATION DATES to reduce the time period.
  • The related Metadata Exercise investigates the CRUISE LIST, but we will ignore it now

Click VIEW DATA DISTRIBUTION PLOT.

7.  Here are all the data we specified, for Liberia.  Notice the heavy concentration of nearshore stations (which is typical), and also the long north-south survey lines -- probably taken during some sort of special project.

Click on DOWNLOAD DATA.

8.  Set up the data download as you see here:
  • WOD NATIVE ASCII FORMAT - required by Ocean Data View software; actually GZipped
  • DATA IN SEPARATE FILES - Never combine different data types in the same download file.
  • OBSERVED LEVEL DATA - The original measurements; standard level data would only be estimates
  • CHOOSE XMT/MBT CORRECTIONS - You can study this issue on your own later.  It has to do with how fast the probes fall through the water, and how depths are estimated from fall-times.  Unless you have a personal preference, just leave it at NO CORRECTIONS for now.
  • The 2 options on the right side, "COMMA DELIMITED VALUE" and "NETCDF FORMAT" are not needed in this exercise, so they are ignored and not shown

 

9.  Enter your email address (one that you can use this very day), and click EXTRACT DATA
10.  This status message tells you that your data are being prepared for FTP transfer.
11.  Within a few minutes, you'll receive an email like this.  Right-click on the FTP link and select SAVE AS.
12.  What to do with the data?
  • Save the OSD file in DATA > OCEAN > WOD > OSD with the filename osd_all_liberia_wod.gz.  Do NOT unzip this file.  It will be used by the Ocean Data View software in zipped form.
  • Similarly, save the other CTD and PFL files into their separate similar folders, with the automatic filenames provided by WODselect.
  • But, because they are so similar in content, you might save the MBT and XBT data into a single folder named XBTMBT.
13.  Do NOT unzip these files.  They will be used by the Ocean Data View software in zipped form.
14.  For data security, you can optionally rename these files (or make copies) with these filenames (changing the date, to today's date):
  • ocldb1424265618.9272.OSD.gz  --> osd_20150218_liberia_wod.gz
  • ocldb1424265618.9272.CTD.gz  --> ctd_20150218_liberia_wod.gz
  • ocldb1424265618.9272.XBT.gz  --> xbt_20150218_liberia_wod.gz
  • ocldb1424265618.9272.MBT.gz  --> mbt_20150218_liberia_wod.gz
  • ocldb1424265618.9272.PFL.gz  --> pfl_20150218_liberia_wod.gz

Both names are perfectly acceptable, and you may encounter either or both in the ODV exercises.

14. 

osd_all_liberia_wod09.gz - Legacy file from August 10, 2010, in case you can't use WODSelect today. From an older WOD version, but suitable for practice work.