Visualizing "From" or "Toward" Current and Wind Particle Trajectories in IDV

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9.38 Visualizing "From" or "Toward" Current and Wind Particle Trajectories in IDV

Exercise Title: Visualizing "From" or "Toward" Current and Wind Particle Trajectories in Integrated Data Viewer (IDV) Abstract: How to use U and V vector grids to map particle trajectories, either from a selected point or area, or toward a target point or area. The method works with any time-series of 2D or 3D grids of U and V values, compatible with IDV. Successful visualization requires that the product of total time interval and an "average" velocity significantly exceeds the grid scale, so the tracks are visible. Preliminary Reading (in OceanTeacher, unless otherwise indicated): N/A Required Software: Integrated Data Viewer (IDV) Other Resources: XIDV file for SE Asia/Oceania forward-time currents from OSCAR for March 2014 - Example surface currents display made in 9.36 Visualization of Remotely Sensed Currents (from Winds and Sea Height) in IDV: OSCAR Author: Murray Brown Version: 2014-04-30
1. Download the above XIDV file to a convenient location. [XIDV files are "project"-type files that list the contents of an IDV visualization and the settings selected for the different objects. If the objects are all online, then you can send the XIDV file to anyone for local viewing without the need to send data.]
2. Run IDV (preferably the latest version)
3. Select FILE > OPEN and navigate to and select the XIDV file.
4. To clear any existing files in IDV, make this choice and click OK.
5. After a few moments, while the data load and IDV creates the map, this image will appear. Note that it is a multi-day surface current map. The times overlap the Flight 370 incident.
6. You can right-click on the DATA SOURCE item, and select PROPERTIES.
7. Very conveniently, IDV shows you the existing choices for the times, but you could optionally change them here with USE SELECTED if you wish.
8. Also the spatial subset is shown, but it can still be modified, if you wish.
9. But we will make a completely new visualization, so you can UNCHECK the FLOW VECTORS item in the right-side menu. The arrows all disappear.
10. In the FIELD SELECTORS main menu, make these selections to begin the trajectory process. Then click CREATE DISPLAY.
11. This small window opens, where you select the grid to use. You can select the GRID 2D TRAJECTORY again, if you want plain colored vector arrows. But the better choice is SPEED FROM U & V to color the arrows. Make that choice, and click OK.
12. After slight wait for the data to load, look for these controls on the DISPLAYS tab. LEVELS - Usually the top depth for 2D ocean currents; could be other levels for 3D models POINT - You can select a single point manually to begin the mapping CLOSE POLYGON - You make an irregular polygon, and IDV begins many trajectories within it; uses the spacing from the source grid RECTANGLE - You draw an easy rectangular box and IDV starts many trajectories within it; spacing as above SKIP FACTOR - Factor to delete points if they are too crowded; 5 gives you every fifth point, for example BACKWARD TRAJECTORY - Draws trajectories that arrive at the specified point or area, not travel from. CREATE TRAJECTORY - Start over and draw new trajectories; you might have to use the time-series control over the map to make it begin
13. Select POINTS, and then click on the location you want on the map. [There is no apparent method yet to read a file to do this.] Then click CREATE TRAJECTORY.
14. After a short wait, a trajectory is drawn from the selected point. Just be patient. If nothing appears, then try the animation control to force it, or perhaps you need a longer time period. Keep trying and it will work. HINT: You can zoom in IDV with SHIFT-CURSOR.
15. And here is the same location with BACKWARD TRAJECTORY set. In general, the POINT option does not produce a visually arresting figure, and it may not reflect the "big picture" that an aggregate of many tracks would show. It is usually wiser to use the CLOSE POLYGON or RECTANGLE option to see multiple tracks.
16. Here is an example of using the RECTANGLE setting. Just drag an appropriate figure on the map. Then click on CREATE TRAJECTORY. NOTE: There is apparently no method yet to specify exact coordinates via a file or direct input.
17. After a short wait, here are the trajectories from that rectangle. You can see that meso-scale circulation features present in the area organize the tracks into about 6 or 7 dominant directions where particles might go. It's very interesting to use IDV to explore the effects of different sized source areas on dominant directions, or target areas (for BACKWARD visualizations).
18. Here is a visualization of a slightly different area, but with a skip factor of 3. Use of a skip factor is entirely up to you; perhaps it clarifies details, but also it might eliminate aggregate trends.
19. What about that "COLORED BY PARAMETER" phrase in the map menu? Select the DISPLAYS > LAYOUT menu. Edit the SPEED color table (IDV expects winds, but we have currents) to a range of 0 to 0.25 m/s (a pretty good current in the open sea).
20. And here you can see the effect of the better color scale. Slow and fast current features are easily seen.
21. Now you can save your work, for easier restoring. Just select FILE > SAVE AS and you can save it in an XIDV bundl
22. This method can be used separate from or combined with the vector arrow-drawing method or its streamline option. Try different experiments to see what works best, and how to set it up for good clarity, i.e. don't make it too cluttered.