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 > 9. Operational/Synoptic > 9.34 JPL/MUR SST

9.34 Visualizing Operational Satellite-Measured Surface Temperatures in IDV:  JPL/MUR

 

1.  Open the main MUR website page and take the time to read about the products.

In the left-hand menu, click on DOWNLOAD DATA.

2.  Which reveals this listing of main products.  On your own you can explore the 3 main options on the left for DATA DOWNLOAD.  But we want to click on FROM THIS PO.DAAC WEBPAGE in the center (which allows online subsetting).

3.  You'll then go to this FTP directory of annual folders.
4.  Find and open the current year (2015 in this case).

Of course, you might not need operational data, so any other year back to 2002 is also easily available here.

5.  You'll find a very long list of day numbers (and dates) for the current year.  Scroll down to the last one.  This will often be the current date, when the data were added to the archive.

Click on that day number (267 here).

6.  And here you can see the 4 available files:
  • *.bz2 - Zipped data file
  • *.bz2.md5 - Quality control checkfile for the data file
  • *.xml - Metadata about the data file
  • *.xml.md5 - Quality control checkfile for the metadata file

The data of this retrieval is 9-25-2015, and the data are from the previous day, 9-24.  This availability is about 3 days faster than previous MUR work in MDL exercises.

7.  The most important link is to the zipped data file, *.bz2, which IDV can automatically open and subset as needed. 
  • Block and copy the BZ2 link.
8.  Take a minute to examine the other 3 files to see what they are or if they can even be examined.
9.  So we need to see what we can do with IDV.  Open it, as usual.

10.  Select DATA CHOOSERS > GENERAL > URLs.  Then for DATA SOURCE, pick NetCDF.  And for the URL, enter the BZ2 link you copied above.

  • Then click ADD SOURCE

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11.  The grid appears in IDVs menu of sources, and you can now see the 4 scalar values in the NC grid.  We want SST (sea surface temperature).
12.  Right-click on the data source link on the left, and select PROPERTIES to begin subsetting the global data down to Liberia's area.
13.  We can make many selections here, but the most important is usually the SPATIAL SUBSET tool. 

Use your cursor to draw a small box anywhere near your area of interest.  This places temporary coordinate values in the 4 small spaces.

14.  Now edit these temporary values (9, -3, -6 and -23) to be your desired area-of-interest coordinates for Liberia..
15.  Before we leave this PROPERTIES window, notice that there is a capability to use STRIDING to reduce the number of data values.  For example, if the spatial subset is still very large, you could reduce the data by selecting a stride, as you see here.  We will not do this now, because the Liberia area is rather small.

Return these values to their original settings, UNDEFINED or ALL POINTS 

Then click APPLY.

16.  Now IDV knows what area you want to see, and you can select what image product you want.
  • Open the 2D GRID menu of fields and select ANALYSED SEA SURFACE TEMPERATURE
  • Open the PLAN VIEWS menu of displays, and select COLOR-SHADED PLAN VIEW
  • Be sure to come back later and try other displays

Then click CREATE DISPLAY.

17.  And this colorful map opens.  To the right of it is an object list, and you can open the dashboard to make changes in the color palette or value range, as you see fit.  Many other IDV exercises cover the settings and how to use them. 

This is the highest resolution, global, Level 4, SST satellite imagery freely available in the world today.  You may want to begin a local subset archive of your own, based on the steps illustrated here.

18.  Now we'll find out how to save this subset of the data in a new NetCDF file of its own.

Select DATA > FORMULAS > EXPORT > EXPORT GRID/IMAGE TO NETCDF

19.  Be careful to select exactly the same choice that we made above, i.e. not in IMAGERY, but in COLOR SHADED PLAN VIEW.

Then click OK.

20.  This rather strangely worded window opens.  It says SELECT INPUT, but it means the name of the OUTPUT.  So use the SELECT FILE control to navigate to the folder PRODUCTS > IDV > NC and enter the filename you see here.  Then click OK.

21.  IDV now asks you to select the specific variable to export.  You can select TEMPERATURE here again.  Then click OK.
22.  Very shortly afterwards, the desired subset file appears where you wanted it.
23.  The new NC file is ready for all sorts of analysis and synthesis work with other data.  Display in Saga is easy, using TOOLS > IMPORT/EXPORT > GDAL/OGR > IMPORT NETCDF:
  • TRANSFORMATION - Checked (yes)
  • INTERPOLATION - Nearest Neighbor

If you don't select these options, then the grid is not georeferenced properly, and is displayed upside-down.

24.  And here is that image in Saga, to show you how it would appear.