So my comments about a long record were thinking that only an effort by Chris Reynolds or yourself with NSIDC data would get a long record of area without the grid size problem. Being able to test different options like including or excluding lakes and/or other areas outside regions to see what is better for prediction would be interesting.
Having the PIOMAS data broken down into regions has proven (at least to myself) very useful. For some time I've wanted a long term record of area/extent in regions - in a numerical format. The problem with what Wipneus has found with CT Area is that the use of a single grid cell area makes the entire series fundamentally unphysical - IMO. Something better has to be done, and using NSIDC gridded data (NASA Team) is an opportinity worth taking. What Wipneus is doing with greater resolution data is still of value, I just want a series back as far as possible to give current changes context.
I've got tomorrow off work to have another crack at this, tiredness has meant I've made a mental note of issues like the Great Lakes (and other lakes) then failed to consider. Thanks for prompting me Wipneus. Omitting the lakes (by editing the land mask manually - in a spreadsheet
) gives the extents, and error shown in the attached image. The error is still at least an order of magnitude greater than that with which I would be satisfied. Ideally I'd like to get no difference, but as I've found with the PIOMAS data, an error may be present due to factors like rounding.
I spent last night using a hex editor to examine the concentration and grid box area files and ensuring I could indentify values from the arrays into which they're loaded and the expected position in the source binary files - the upshot being that I am correctly loading arrays with data that reflects the source files. So it's not an issue with some mismatch there. The closeness of my extent calculations and the NSIDC Extent series argues against such an error anyway, but I wanted to be sure before moving on.
PS, due to the extreme losses in 2012 I also think it worth downloading a less extreme year and looking at errors in such a year.