Visualizing Satellite-Measured Wind Speed & Waves in IDV: AVISO
Gridded Data Extraction Tool (GDET)
In this exercise you'll return to the AVISO GDET tool to obtain
satellite analyses of winds and waves. Using methods used for sea
surface height in 9.8
you'll learn how to make maps of these parameters. THIS LESSON
IS PROVIDED FOR EDUCATIONAL PURPOSES ONLY. NO ONE SHOULD ATTEMPT
TO RELY ON THESE ANALYSIS PRODUCTS FOR NAVIGATION OR FOR ANY OPERATIONAL
PURPOSES AT SEA.
Preliminary Reading (in
OceanTeacher, unless otherwise indicated):
|1. Open the main AVISO
website. [There are English, French and Spanish versions; see the bottom left
corner for the links]
Take some time to read though this very powerful
site, and find out what sorts of data and data products it offers.
Results range from highly detailed, single transect satellite passes, to
very generalized geographic grids of high-level products.
|2. Select DATA > ACCESS to see these
7 items. They offer an extremely broad set of access methods, which
you should explore later on your own. They differ in the timeliness of
the of the data, and other technical details.
NOTE: You can alternately
choose the DATA > PRODUCTS tabs to go through a more generalized
introduction to the whole product suite at AVISO.
Select GRIDDED DATA EXTRACTION TOOL (at the bottom)
|3. You'll see a very large page
with this text at the top:
This is the point where you could
SUBSCRIBE to get these data. This is the same registration process
that you may have used previously to use Marine Data Literacy exercises for AVISO data; if you're not sure, then try to pass this step and see what
happens below. You'll have opportunities there to register, if
|4. Lower down on this same large page, you'll
see these available data types:
|5. This is what you'll see in the WIND/WAVE products
section. We'll begin by clicking the DATA REQUEST FORM beside GRIDDED
SIGNIFICANT WAVE HEIGHT.
6. At this point, you must have already
registered with AVISO for FTP and/or gridded data extraction services at the address listed above.
Either way, this is what you need:
When you click on either DATA
REQUEST FORM controls, you'll need to enter these items to continue, or
take the time to register now.
|7. Enter your information in this form, then click
|8. This is the opening screen. Enter these options:
- Select Output - NetCDF
- Selection Region - Don't touch
- Select Time Range - Set a reasonable recent span of a few days,
for example the most recent week.
- Available data appear to
range from 2014-04 to about 3 or 4 days prior to the present
- NSEW - Enter appropriate values for your area of interest; in
the case of Liberia, they are:
- Top = 9
- Bottom = -6
- Left = -23
- Right = -3
- Variable Download - Check the data you want; for this
exercise you can check only SIGNIFICANT WAVE HEIGHT
On your own time later, you can explore these fields. Now click
DOWNLOAD (lower left corner).
|9. Your download should begin shortly. If it does
|10. Save the data to the folder DATA > OCEAN > AVISO with the filename
|11. As usual, we can check the validity of the data
in ncBrowse. Here are the first 2 windows in ncBrowse. When
properly set, you can click on GRAPH VARIABLE to see a map.
The units are meters.
|12. And here is the data map, with a scale.
|13. You can use exactly the same steps as
above to obtain and save the windspeed product (Panel 5, above). Then
save the resulting file to the folder DATA > OCEAN > AVISO with the filename
|14. Here is the wind file in ncBrowse. Note
that the AVISO products are extremely honest, and they blank out areas which
don't meet their quality or operational criteria. Hence there may be
diamond-shaped areas of no data.
|15. OPTION: For correctness, you
can change the filenames as you see here, to help you recognize the files
|16. Run IDV.
|17. In IDV, use the standard DATA >
DATA CHOOSERS. Make sure the DATA SOURCE TYPE is set to GRID FILES (NETCDF,
ETC.). Then navigate to and load the wave height and windspeed files
you have created and saved on your PC.
|18. WAVE HEIGHT DISPLAY: Select the wave height
object. Then make these FIELDS and DISPLAY choices. Then click
|19. And here is your wave height map. As
with other data sequences in IDV, you can show or save an animation, using
VIEW > CAPTURE.
20. Using the same steps, you can map the windspeed
raster in IDV also.
|21. And if you want to use an evenly spaced color
palette, here both maps have been set with DASHBOARD > COLOR TABLE > RADAR >
DBZ to a familiar rainbow.
|22. Now you have the basic datasets, you
can make all sort of related analysis, such as value histograms, time-series
probes and animations. See
9.3 Visualizing Modeled Wave Analysis Grids in IDV:
Wave Watch III for some help on how to make these.