By PM i got the following question:
: Wipneus March 01, 2015, 08:00:03
Jaxa AMSR2 data for 20150227 is similar, with Baffin dropping at the same rate as the Bering region. [...] Total Extent -112.4
I'm puzzled by this figure, as the official IJIS numbers do not indicate a century drop here.
What am I missing? Are you excluding lakes or other areas that I am not aware of?
First, I calculate regional extent and area data from a number of satellite derived sea ice concentration data sets. I do this because:
- regional data is hard to get;
- area data is not provided;
- calculation details differ, e.g. is lake ice included?
Now the question why century yes/no, while they both use Jaxa data. Since in this time of the season concentrating on the largest peak is a study in noise, whether weather related or any uncertainty in the chain of measuring and analysis. Comparing my Jaxa data with the Jaxa/IJIS/IARC extent I can think of the following differences.
- there is no IJIS or IARC in my calculations. I do not know all the what's and the how's of what eaxctly they do;
- For the totals, I only include at this moment the 14 well known regions. Since the IJIS/IARC extent data are consistently well above mine, I guess they include all of the ice. It is not sufficient though, even including all the ice my calculations are still a bit below.
- timing: correlating changes in both measurements show that my calculations lag those of the IJIS/Jaxa numbers. A difference of 12 hours would explain my observations.
- Averaging, they seem to suggest that a 2 day averaging period is used (3 days for the Windsat era). There is no averaging in my calculations;
- the data source: I am using Level 3 data from Jaxa, that is already processed to some degree. Level 2 data would be an option. I have no idea what the IJIS/IARC calculations use.
- homogenization: IJIS/IARC offer continuous data since 2002 even with different sensors. Some compensation for the differences is likely to make them comparable. Details are unknown.
I publish the data as soon as it is calculated, locations are summarized in
this post.For Jaxa, I use L3 sea ice concentration available
here, free registration required.