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 > 9.7 MET.NO Ice

9.7 Visualizing Satellite-Measured Sea Ice in IDV: Norwegian  

Meteorological Institute

 

1.  You really must read through the excellent Product User's Manual (link above) to get an overview of the ice data products available from MET.NO.  Information below provides a terminology overview, and does not do justice to the richness of these resources.  To orient you to ice data terminology, here are some important terms.
2.  Sea Ice Concentration (given as a real number):
  • 0-100: Area fraction of ice (%)
  • -99: Over land
  • -199: unclassified
  • -32767: No data

Accompanied by QUAL files containing quality flags for each pixel.  Just for your interest, using ncBrowse, the author found these flags in the metadata for the NetCDF file.  They would be the values in the QUAL grids.

  • 0: Nominal value from algorithm used
  • 2: sea ice algorithm applied over lake
  • 10: background data used for setting the value
  • 14: Value set using an ice type mask
  • 100: missing value due to over land
  • 101: missing value due to missing data

The term "nominal value" means accepted data value.
3.  Sea Ice Edge (classified grid):
  • 0: No data
  • 1: Ice free
  • 2: Open ice (35-70% concentration)
  • 3: Closed ice (70-100% concentration)
  • 9: Over land
  • 10: Unclassified

Also have QUAL files.
4.  Sea Ice Type (classified grid):
  • 0: No data
  • 1: Ice free
  • 2: First year ice
  • 3: Multi year ice
  • 4: Ambiguous
  • 9: Over land
  • 10: Unclassified

QUAL(ity) files are also available.
5.  There are several source of these data products, including both data download and direct connection sites (i.e. OPeNDAP).  In the panels below, we'll use the OPeNDAP "cloud" approach.  This avoids any need to download files, to go through a second-level distributor or to register for the service.
6.  Open the Ocean and Sea Ice Service website.  Click on the TILGANG TIL DATA (=Access to Data) control in the menu of services.  There is an English version, but it's more fun to work with the Norwegian version.

You can use Google Translate to render the labels here as follows:

  • Sea- and IceService
  • Information on sea and ice and access data from Norwegian waters and the Arctic from the Norwegian Meteorological Institute.
  • Use the menu on the left to find information, view and download data
  • Last updated ice charts from Istjenesten
     

 
7.  Near the middle of this page, you'll find this table:  DIRECT ACCESS TO SPECIFIC DATASETS.  [The 4 links are better explained below.]
8.  These are translations for the 4 lines above, in the DIRECT ACCESS table:
  • Iskonsentrasjon = ice concentration or coverage (see table of values above)
  • Iskant = ice edge (see table of values above)
  • Istype = ice type (see table of values above)
  • Isdrift = ice movement
  • THREDDS adresse = special URLs for the THREDDS servers that deliver these data (see next panel)
9.  These are the URLs you can find for each of the 4 links:
10.  To use any of these URLs (which are actually catalogs in the THREDDS system of data access, you much change the filename extension from html to xml.  For example, the first one would be:  http://thredds.met.no/thredds/catalog/osisaf/met.no/ice/conc/catalog.xml.  And so on.  We can use these catalogs in IDV, as you'll see below.
11.  Run IDV.

12.  In the dashboard page, select DATA CHOOSERS > GENERAL > CATALOGS.  Then enter the first catalog address you obtained above.
13.  Click RETURN, and this menu will appear.  Navigate down into it to find the latest northern hemisphere (NH) ice concentration file.  In this example, the author was searching on July 7, 2013.

When you select the latest NH file, then click on ADD SOURCE (at the bottom).
14.  These file contents will be listed (under 2D GRID).
  • Select CONCENTRATION OF SEA ICE
  • Select COLOR-SHADED PLAN VIEW

Then click on CREATE DISPLAY.
15.  This ice concentration map (or very similar) will appear.
16.  Optionally, you can improve the color palette, by selecting DASHBOARD > COLOR TABLE > RADAR > DBZ, which results in a very common rainbow selection.
17.  Here's a zoom (SHIFT + ZOOM-IN) into the area between Greenland and Iceland.

You can see that the analysis does not include the area very close to land, which is blanked out in most Norwegian Met ice products.
18.  So much for the ice concentration.  Now we'll look at the ice edge products.
19.  Change the catalog entry to specify ice edge.  Then hit RETURN.
20.  Make these choices and click CREATE DISPLAY.
21.  Here' the ice edge map, zoomed into the area of the Antarctic Peninsula.  You can see that IDV has trouble with classified datasets, such as the codes you see above in Panel 3.  IDV is trying to display the values as if they were on a continuous spectrum of values.

We can easily see colors for values 1 (ice-free), 2 (open ice) and 3 (closed ice), however.
22.  Now we'll look at ice types.
23.  Change the catalog, as you see here, then hit return.
24.  Make these choices, then click CREATE DISPLAY.
25.  This map, seemingly without features appears.  The problem is that the codes for type only go from 1-10, but there is apparently a filler value of 255 somewhere in the file.  You can see this in the palette value along the bottom right edge.
26.  Go to DASHBOARD > COLOR TABLE and select again the rainbow palette.

Then right-click on COLOR TABLE and elect CHANGE VISIBLE RANGE.  Set the range to be from 1 to 10, and click APPLY, and click OK. 
27.  Now you can see the very restricted palette range of 1 to 10.

It is very difficult to know exactly what value is represented by the rather "green" large area of the map.  This again is a failure of IDV to handle classified data well.
28.  Here the area of the Kara Sea has been blown up, so that the colors are easier to see.  Apparently the larger area is code 3 (multi-year ice) or 4 (ambiguous).  The smaller, bluish area is 2 (first-year ice).  The dark blue area is 1 (ice-free).

IDV probably needs a method to specify single values for colors, to accommodate classified data grids.
29.  Examination of the final data product, for ice movement, indicated that at least on this date and for the Northern Hemisphere there were no values.  We'll monitor this situation to find out where, when and if you can get values to plot ice movement.
30.  Any and all of the above analyses can be saved in IDV with the FILE > SAVE AS function, using the XIDV filename extension to denote a specific display of a particular remote file.  Just re-open the XIDV file, and IDV will go to the Norwegian site to get and display the desired data.