The nice guys at the University of Hamburg have provided the results of their unfinished sea ice concentration calculation based on L1(R) AMSR2 data from JAXA online in some very handy NetCDF files.
Citation of source data:
Beitsch, A., L. Kaleschke and S. Kern (2013), "AMSR2 ASI 3.125 km Sea Ice Concentration Data, V0.1", Institute of Oceanography, University of Hamburg, Germany, digital media
(ftp-projects.zmaw.de/seaice/), [BEGIN Jan 2013- present];
Spreen, G., L. Kaleschke, G. Heygster (2008), "Sea Ice Remote Sensing Using AMSR-E 89
GHz Channels", J. Geophys. Res., 113, C02S03, doi:10.1029/2005JC003384.
Kaleschke, L., C. Lüpkes, T. Vihma, J. Haarpaintner, A. Bochert, J. Hartmann, G. Heygster,
"SSM/I Sea Ice Remote Sensing for Mesoscale Ocean-Atmosphere Interaction Analysis",
Can. J. Rem. Sens., 27(5), 526-537, 2001.
[EDIT 2017-03-30: source adress change]ftp://ftp-projects.cen.uni-hamburg.de/seaice/AMSR2/
The data is provided at a 3.125x3.125 km grid.
Summing the area of the grid cells that have an ice concentration of 15% (or some other value) should give a measure of the extent that can be compared with the well known Jaxa/Ice, NSIDC and others that do similar calculations.
Here I present the first results.
The calculations have the following features:
1) uses the actual area of the grid cells, which may deviate a few perecent from the nominal 3.125^2 km2
2) Ice concentration of the "North Pole hole" is calculated to be the same as a small ring (width 25% of the radius of the hole itself) around the hole;
3) Spurious ice is removed from coastlines where there is open water within a "few" grid cells;
3a) pixels labeled as sea, separated from the world oceans are considered "lake" and discarded;
4) "phantom" ice fleets that appear and disappear randomly, especially at lower latitudes are detected and removed;
5) an ice mask is used to split the area into regions as closely as possible similar to those of the Cryosphere Today.
Of course it may be regarded as a foolish undertaking:
1) the 3.125 km grid cannot be compared with anything else available;
2) the 3.125 km ice concentration values are influenced by clouds and water vapor (as a consequence of using the hi-res 89 GHz microwave band);
3) The ice concentration data is unofficial and work-in-progress;
4) The data is only available for 2013, we cannot compare with any other year directly.
Well, it is fun to try and I was supprised when I saw the first result:
My calculations have been tracking Jaxa's quite close.
I expected a lot of noise as there is no filter (Jaxa filters 2 days), the unfiltered data looks quite usable.
Since end of May, the two have been diverging. This is to be expected, when hole fall in the ice cover the smaller grid will more likely pick them up than the wider grid.
1) extent per region;
2) area calculation;
3) compactness calculation (like CAPIE but from the same source)
[update put the area graph in the top post:]
[update put the compactness graph in the top post]
[update: add regional graphs]