Thanks Wipneus.
One question : your map suggests that the CAA seriously expanded in extent and area (lots of solid blue there) yet your numbers suggest that the CAA increased only 1.1 in extent and actually dropped 6.0 in 'area'. Why the discrepancy ?
Thanks for the questions Rob, I wondered if anyone does notice.
The delta images are taken created from the data as I download from the Uni Hamburg ftp server. The only processing that I do, as is intended by the creators of this data, is to apply a stationary land mask that comes from the Uni Hamburg as well.
These data, lets call it "raw" data, show two obvious defects. The first one is the false ice along coastlines that you can observe are in all likeliness ice-free. This is due to land spillover of the microwave sensors. For area and extent calculations I filter these pixels away, based on the distance from the coast (few pixels) and from the ice free ocean (few pixels max away). I currently filter about 300k of extent away, and about 150k in area.
The second defect is what I call phantom ice, showing as an abrupt change of a cluster of pixels changing from on one day near zero concentration to a substantial value (>=17%).
Reason for this is unknown to me, but the favorite concentrations of such phantom ice are 50%, 33%, 25%, 20%, 17% gives an idea what could be happening.
I do filter such phantom ice before calculating extent and area. Note that if the ice was not phantom but a genuine uptick in ice cover, it will no longer be filtered the next day (since the zero ice condition on day one is no longer fulfilled).
Looking at the numbers for the CAA, I think the filters are doing a good job. But without the excellent and reliable quality of Uni Hamburgs data that would not have been possible. Uni Bremen has a similar product (AMSR2 ASI 3.125km) but it is proving much harder to get the smooth extent and area data from.
That should be some answer to your first question, the fact that we did not see a bump in today's report indicates that the filter algorithms must have worked well.
Why area and extent can go different directions is all in the definitions of area and extent. Area can in some cases change a lot without having any impact on extent (consolidated ice), where in other cases (marginal ice) a small area drop can cause a big change in extent. The CAA contains both types of ice, so you are bound to see such variations.