Visualizing Operational Drifting Buoy Trajectories in IDV: GDP

Marine Data Literacy

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9.23 Visualizing Operational Drifting Buoy Trajectories in IDV: GDP

Exercise Title: Visualizing Operational Drifting Buoy Trajectories in IDV: GDP
Abstract: In this exercise you'll examine the Global Drifter Program (GDP) website resources, and download recent data (in ASCII spreadsheet format). These data can be loaded into IDV as "text point" data, requiring some novel manipulations. Using an existing trick n IDV to limit data displays to certain time periods, the trajectories can be displayed visually as "recent" (RED) and "very recent" segments (GREEN), to show the direction of flow. The complete visualization is saved as a generic "template" that can be used for any 2-week dataset from the GDP. Changing the time period and various display options (e.g. color) is easy with IDV's controls, demonstrated below.
Preliminary Reading (in OceanTeacher, unless otherwise indicated):
- N/A
Required Software:
- Integrated Data Viewer (IDV)
Other Resources:
- Global Drifter Program (GDP)
- Surface Drifter Pair Spreading in the North Atlantic - Good explanatory paper from the GDP scientists
- World Meteorological Organization (WMO) Systems
- Date and Time Formats
Author: Murray Brown
Version: June 2013

1. This is a relatively long exercise, due to the many setup steps involved. But the good news is that when you are finished, you'll have a template that will direct IDV to make a drifting buoy analysis with only about 3 clicks.

2. Open the GDP webpage and read about the overall program. Then find and click on DATA AND PRODUCTS, in the left-hand menu.

3. Read more about the program on this page, then click on GTS DATABASE.

NOTE: GTS is the Global Telecommunications System of the World Meteorological Organization Systems (see above). The GDP program managers use this acronym to denote Near Real Time (NRT) data.

4. This is the data display for the NRT data.

5. For DATA SET select GTS BUOYS.

6. Use the rubber band box to draw a rectangle that roughly covers the mid-Atlantic.

7. In the times section, enter dates that cover the most recent month.

Of course, you'll want the most recent dates, and perhaps a different time-range. That's up to you.

8. Select GRAPHICS for the output type, and click GO.

9. Examine the output map for data in or near the Liberia area. In this case, there are none, so we'll focus on several tracks offshore Senegal.

10. Use the provided rubber band box to draw a smaller map offshore Senegal.

11. Click on GO to enlarge the map area. For your orientation, Dakar (the capital) is located at the tip of the Cap-Vert Peninsula visible at +15 degrees latitude.

12. Change the product type to DATA and click on GO.

13. This indicates your data are ready to download.

14. Use SAVE TARGET AS and navigate to the folder LIBERIA > DATA > OCEAN > GDP and save the file as trajectories_20130521_20130621_senegal_gdp_miami.dat. We're keeping the original extension DAT to indicate the data are still in the GDP format.

15. Below, you can see an image of the DAT file's top data rows. Checking with an ASCII editor, you can find that the columns are mainly separated by TABS, but the DATE and TIME columns are separated by a SPACE. This is perfect for what we need to do in IDV.

16. Run IDV.

17. Use the dashboard DATA CHOOSERS to find the first (i.e. earliest) data file. Then click ADD SOURCE.

18. This is IDV's point data (or spreadsheet) reading utility. We must make several changes and selections.

19. Select DELIMITER = TAB and you'll see that the header row is correctly read.

20. In these rows, use the drop-down menus to connect these incoming value names ("Lat", "Lon", etc) to their correct NetCDF names.

NOTE: Other connection could be made, but they aren't needed and they would greatly increase the size of the data loading.

21. Comparing the time format actually used in the data, we see that this small change in the FORMAT column is needed.

Delete :ss

22. Possibly not needed, but good practice: Place -99999.9 in these rows of the MISSING VALUE column.

23. Finally, use the UP or DOWN arrows to scroll the spreadsheet to the first data line.

24. Now before we do anything else, we can save the above settings.

Select PREFERENCE > SAVE CURRENT

25. Enter the name GDP Tracks for these spreadsheet-reading rules. Then click OK.

26. Click OK to load the spreadsheet.

OBVIOUSLY we have presented an extremely simple spreadsheet import process in the above panels. In real life, working with other types of spreadsheet data, you'll need to study your data carefully and possibly perform experiments to find the best method.

27. If everything has gone OK, you'll see the familiar IDV dashboard FIELDS and DISPLAYS panels.

28. You can see that IDV is asking you for a "Layout Model" for the diplay of the data, but we don't have one yet. In the next few steps, you'll use a special editor in IDV to create one.

29. Select TOOLS > LAYOUT MODEL EDITOR

30. This is the LAYOUT MODEL EDITOR where we can specify how the data will be shown on the maps. You can ignore the settings and objects you see now, because we will create new ones.

31. To make a new layout, select FILE > NEW and enter this name. Then click OK.

32. From the menu of available objects, click on SHAPE to select it. It becomes highlighted..

33. Then click on the center of the layout area to place a shape there.

You will need to adjust the shape to the center, manually.

34. Right-click on the object and select PROPERTIES.

35. Make these selections:

SHAPE = FILLED SQUARE (other shapes don't seem to work as well)
FOREGROUND COLOR - Click to CLEAR
BACKGROUND COLOR - Click to select RED from a palette
SCALE SIZE - Leave unchanged; can be adjusted elsewhere.

36. Click OK> FILE > SAVE to save this layout as LOCATIONS RED.

37. Use these same steps, but select the BACKGROUND COLOR = GREEN to create a separate layout model named LOCATIONS GREEN. You can close the LAYOUT EDITOR now that you have made these 2 new layouts.

38. Now you are back to the FIELDS and DISPLAYS panels.

Select LAYOUT MODEL: LOCATIONS RED (middle of right side)
And finally, now you can click CREATE DISPLAY (at the bottom)

39. Click YES.

40. On the dashboard, select DISPLAYS > LAYOUT.

DECLUTTER: Uncheck
LAYOUT MODEL: Locations Red
SCALE = 0.1 (can be adjusted later, if needed).
You must click APPLY afterwards.

41. Select DISPLAYS > TIMES

Chance INDIVIDUAL to MULTIPLE.

42. Check your map, and it should look something like this (depending on the actual data you obtained).

NOTE: You can go back to the DISPLAYS page to make changes in real-time to your map, if needed.

43. Now return to the FIELD SELECTED tab of the dashboard, and click CREATE DISPLAY to make a second map.

44. Make the same choices for LAYOUT, with one big difference:

For LAYOUT MODEL: Locations Green

45. For TIMES, also select MULTIPLE.

46. But we must set the time range differently, so click on RANGE. You'll see this control panel:

Change START TIME to RELATIVE TO END TIME.

Then, to select the time relation, click on START TIME > OFFSET

46. There are about 30 days in the dataset. To see only the last 10 days, make these choices:

Set the sign to MINUS (-)
Set the DAYS to 10

Then click OK.

47. You can you can see the exact time settings for the display.

Click OK if everything looks like this.

48. Now you can see the exact time range for mapping the last 10 days of the data in green.

These settings are already in effect, so you can look immediately at the map.

49. The last 10 days of the data month has now been plotted with almost exactly the same steps, except the LOCATION GREEN layout has been used to indicate direction of movement. [Multiple colors from palettes don't seem to provide an easily grasped product, so we recommend only the red/green dichotomy.]

You can see the southwestward extension of the Canary Current north of Cap-Vert. And large counter-clockwise eddies lie just north and south of it, typical features near very large topographic flexure points.

50. Now, select FILE > SAVE AS and navigate to PRODUCTS > IDV to save this work as trajectories_20130521_20130621_senegal_gdp_miami.xidv.

9.23 Visualizing Operational Drifting Buoy Trajectories in IDV: GDP