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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 > 9. Operational/Synoptic > 9.40 Time-Series

9.40 Extracting Time-Series Plots for Points in 3-D Grids with IDV: Models or Climatologies

1.  Save the above NC file to PRODUCTS > IDV > NC (because that reflects how the author created it from a global file in DATA > OCEAN > PISCES)
2.  Run IDV.
3.  Select DATA CHOOSERS > GENERAL > FILES then navigate to the NC file and load it.

NOTE:  This area subset file does not contain all the data in the original global file.  If you want to examine these data more closely, then go to the Mercator and MyOcean links above.

4.  As always, we first right-click on the newly loaded object and select PROPERTIES.
5.  Select SPATIAL SUBSET to see that the area is exactly what we expected, so nothing needed here.

If you see a global or large regional map here, then this is the place where you'd use SPATIAL SUBSET to limit it to your desired area of interest.

6.  Select TIMES to see that the last item is only about 3 weeks old (on today's date, 2014-8-23), which is practically "operational" in the world of global geochemistry models, as opposed to circulation models whose products can be as recent as daily.
7.  So now we're ready to make data products.  First, select DISPLAYS > PLAN VIEWS > COLOR-SHADED PLAN VIEW.  Then click on CREATE DISPLAY.

8.  This map appears, showing relatively high concentrations along the equator, and very low concentrations near the coast.

9.  Our main purpose here is to make a time-series plot, so find and select this DISPLAY mode, and click CREATE DISPLAY.
10.  This new window will open, actually showing the time-series graph.  There's a LOT of things to learn about this, but we don't have time now.  Come back later and explore how to make multiple graphs, etc.
  • PARAMETER - Nitrate
  • VALUE - We expect values like 0-10 umol/l but it says "missing"
  • MIN/MAX/AVG - Also "missing"
  • LEVEL - Has default of 8000, so this must be a meter height in the atmosphere, and negative values aren't expected!
  • SAMPLING - Weighted average (seems good)

So IDV's time-series algorithm complete misses the ball with ocean data here, and doesn't see the data, as the animation algorithm did above.

11.  Right now we're going to learn the trickiest, hardest-to-discover bug the author has ever found in any software.  You must perform the next 3 panels, or you can never make the graph.
12.  Move your cursor over the LEVEL > PROBE space, and you'll see the RIGHT CLICK TO EDIT message.  Ignore that direction, completely; it is wrong.
13.  Now, use a LEFT click to edit for probe depth.  Select the first numeric value you see.

NOTE:  The latitude (1.4) and longitude (-13) now appear in the spaces along the bottom of the graph.


14.  Now, you should see an empty graph (but with index lines and proper dates), with appropriate values inserted in the spaces below it.

15.  To modify the graph, right-click on the NO3 line (dark blue above), and select PARAMETER NO3 > CHART PROPERTIES.
16.  Now you see the controls for this specific graph, which you can explore later.  For now, just go to RANGE > MIN > MAX and click on the ellipsis (...) to get some choices.

Select the DATA RANGE of 0.0047 to 3.8.

17.  Then when these values appear, you can be creative and select better choices, such as MIN = 0 to MAX = 4.  Then click OK.
18.  Now a beautiful time-series graph appears, based on your selections, and on the location.

Examine this graph closely and try to find where each setting came from, above.

19.  Images can be captured from IDV, with JPG, GIF formats.  Apparently the complete data and display combination cannot be saved as an XIDV bundle, though.
20.  What about location?  When you make the time-series graph, a small icon appears on the main IDV map, showing the location (the default is the center point, evidently).  Here you can see the same time-series as above on the right, and the location of the values on the left.

21.  Here, you can drag the icon to near shore (or you can enter coordinates into the spaces in the lower-right corner), where nitrate values would be very low (due to frantic phytoplankton growth).  The time-series graph goes almost to zero values, so we've changed the range to 0-0.01 (using the control step above), just to see any fluctuation.  The differences between the 2 graphs are extreme.

22.  Once you've seen the trick above to get the tool to work with ocean data (i.e. negative values) then you'll be able to explore this very useful tool and make extremely valuable analysis products on your own.  Please notify me if you find any other problems, or if you come up with a really special image.