Exercise Title: Visualizing
Satellite-Measured Sea Surface Salinity in Integrated Data Viewer (IDV):
Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) via
Abstract: In this
exercise you'll go to the US NOAA CoastWatch site (or maybe it's the
OceanWatch site; who knows?). There you can find lots of
near-real-time products, but the vast majority are regional, not global,
and there are very few in the formats we like for operational products
(especially NetCDF). We focus on the new MIRAS salinity products,
and show how to visualize them in IDV, including subsetting and
Preliminary Reading (in
OceanTeacher, unless otherwise indicated):
Earlier information that this site was being phased out appear to have
been incorrect. It is alive and well, but populated with a
less-than-ideal product suite.
This site has not replaced CoastWatch, and in fact it appears to have
been abandoned. Very messy website now, with dead ends and
MIRAS Instrument on SMOS - New EU salinity products to rival US
|1. Open the
CoastWatch website, and spend some time reading over the resources provided.
[For your information, this site was apparently being converted to a global
facility named OceanWatch, but this has been terminated in favor of a
complete expansion here. CoastWatch folks are invited to let me know
when this situation changes.]
|2. Click on the DATA ACCESS
link in the left-hand menu. Take a few minutes to read over the
You will not use the menu in mid-page, because it
contains many regional or specialized products. We only want products
that are globally available. So we will use the menu system on the
|3. But at the bottom of this
same page you'll find these "ALTERNATIVES". We don't suggest their
use, because at least one of them, the all-important THREDDS link, is
|4. Before we advise you what
to get from this site, please consider these issues:
- Most of the CoastWatch data products are not in optimal formats for
operational use ... especially the HDF!
- Only the SALINITY data are in NetCDF grids, so we limit this
exercise to those data
- CoastWatch folks are invited
to let me know when this situation changes. HDF just won't cut it
anymore, and your user community is looking forward to wall-to-wall
So make any selections you want, but for this exercise, please make these
choices. since Aquarius is covered in a different exercise we'll focus
on SALINITY > MIRAS here.
Then click SEARCH.
|5. After a quick search,
these products are listed. For your own searches later, try to keep
the options limits so you don't get a huge pile of products that are
difficult to pick from.
|6. For this exercise, we
click on the very latest one, SEP 3 (for today, which is SEP 6 for the
Look just below the map, and you'll see what digital products can
be obtained. The NC (for NetCDF) is our main interest. The
others are merely images.
Save the NC file to the folder LIBERIA > DATA > OCEAN > COASTWATCH with
the current filename SMOSCW_S2014246_3day_WW00_sss.nc (or whatever
you have selected).
|7. You can also save the
metadata file (TXT) for permanent record of the contents, etc.
8. Save it in the same folder as the data, with the filename SMOSCW_S2014246_3day_WW00_sss.txt
9. Now we can work with the file in IDV. You'll
need to do some reading on your own to see more about the derivation and
actual contents of the salinity grids. This exercise just shows you
how to work with them as digital objects, not their background or
importance. In IDV you can make these selections to visualize the
grid. Notice there are 3 possible "models" for the calculation of the
salinity, and here we've just picked the middle one out of laziness.
You need to research this issue, compare the products and decide which you
want to use for your own work in the future.
Now click CREATE DISPLAY to see the data map.
10. And here it is, shown using the author's favorite
color palette RADAR > DBZ. Please notice a couple things:
The overall map
is smoother and more "complete" than the the US Aquarius products
numerous "outlier" areas along the African and Asian coasts. These
appears in north-south bands that hint at local data issues
|11. But if you only want
Liberia data, how do you get it? Right-click on the data object in the
left-hand menu. Then select PROPERTIES.
|12. When this window opens,
select the SPATIAL SUBSET tab. Then draw a rectangle anywhere on
the map with your cursor. Then you can enter the correct
coordinates for Liberia, as you see here.
Then click OK.
13. If you have selected the same DISPLAY settings as
above, including the palette, then this is the data map for Liberia subset
from the global grid. In general the values are higher in mid-ocean,
but the pattern is very messy.
|14. To clean up the messy
product, you can go back to the dashboard for the subset map, and select
SMOOTHING > CRESSMAN WEIGHTED.
|15. The grid map
automatically changes to this very smooth, easily understood image.
You can try other smoothing algorithms on your own to select the one that
works best for your data. Or you can always ignore smoothing, and work
with the raw extract; it's all up to you.
|16. If you want
to save this new grid, then use the method in
5.10 Basic Grid Operations, Calculations and
Subsetting in IDV