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SATire
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But if that really would be the confidence limit (typically 95% data inside, equal to 3 sigma or standard deviations), that would mean that something could be wrong with the estimation function or something perhaps systematically changed in nature... Only future can tell.
Toggle Commented Sep 7, 2013 on PIOMAS September 2013 at Arctic Sea Ice
Neven, "Those error bars, large as they are, didn't manage to catch this year's anomalousness. It's clear that statistics has its limits, but this is pretty amazing." As I understood Wipneus those error bars are normal standard deviations. Therefore, about 68% of data should be inside the bars and 32% outside on average. So I would still stay with Wipneus, that the error bars are quite large, since less data than 32% is still outside the bars.
Toggle Commented Sep 7, 2013 on PIOMAS September 2013 at Arctic Sea Ice
Best resolution (but ignore that "smear" due to water vapour): https://0c35ba35-a-62cb3a1a-s-sites.googlegroups.com/site/apamsr2/home/pngcby32/Arc_20130606_res3.125_pyres.nc.png and suitable for your own SIA measurement e.g. to check that CICE prediction (will that 2nd hole show up?): http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticicen_nowcast_anim30d.gif
Toggle Commented Jun 7, 2013 on If this is real... at Arctic Sea Ice
Another drop in SIA in the storm affected region - but like yesterday heavily disturbed by "rain-smear" so I would not consider that as comparable to earlier SIA measurements again. But some "real" black spots and lines open there - so something is happening at last. But if the second region with concentration predicted <50% right in the MYI will really show up, I would like to doubt again for same reasons as stated above. (Refering to this hycom -CICE concentration forecast as usual - because that is directly observable by the map of this thread, if the weather allows for: http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticice_nowcast_anim30d.gif )
Toggle Commented Jun 7, 2013 on New map on the block at Arctic Sea Ice
Those clouds that confuse Bremen's concentration are also very prominent visible in the new maps and disturb SIA measurements - those somehow smeared regions may correspond to that orange-pinkish clouds in MODIS-Alpha. Maybe that is heavy rain or hail? We should try to avoid measurents in that "smeared regions".
Toggle Commented Jun 6, 2013 on New map on the block at Arctic Sea Ice
One could also check the other Navy-prediction, which is a bit more related to the new map on the block. But maybe they do that checking on their own - the 50% concentration in the old storm effected zone becomes smaller from day to day. Instead they have found a new region in the MYI where concentration will drop below 50% in a few days: http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticice_nowcast_anim30d.gif Since the first drop has not been confirmed by observation up to now I would bet the next one will not show up, too.
Toggle Commented Jun 6, 2013 on New map on the block at Arctic Sea Ice
Nice pictures again, A-Team. "In doing science, the data is marshalled first, then secondarily interpreted. Try it some time." You are right - in science I collect data, calculate all possible errors and dicuss every issue silently for a year with collegues prior to publish some original and safe results. Here I used the "look-and-shout" approach which I considered appropriate for blog comments. Maybe I am over-excited that we can do now our own SIA measurements from the new maps and I hoped the storm-effect would be a nice motivation for someone to try it, too. It is bloody simple and I have explained every little detail how to do it. It is better for me to stop posting SIA measurements now at least until someone considers it interesting enough to try it oneself.
Toggle Commented Jun 5, 2013 on New map on the block at Arctic Sea Ice
@Robertscribbler "Sorry, but I'm not convinced this number crunching provides the conclusions you've asserted." Vice-versa Robert. Hycom concentration prediction is based on number crunching while SIA measurement from concentration maps is theory-free plain observation by satellite. Nowhere in the storm affected zone in the CAB I can find SIA concentration < 80%. Can you? In that respect I consider hycom concentration calculation wrong. But this finding is premature due to the fact that it is not reproduced by one of you yet. So please: Check on your own. SIA from 4.6. map in CAB (position 800 1450 ellipse size 600 600): 96.66% of the 2.761 Mio sq km circle. A bit less than the day before but perhaps underestimated due to cloud-features in the map.
Toggle Commented Jun 5, 2013 on New map on the block at Arctic Sea Ice
Robert, this concentration prediction by hycom I intended to test: http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticice_nowcast_anim30d.gif By determing SIA on our own in the very simple way described above we can now test the prediction modell-free - and this test is proving hycoms prediction wrong, doesn't it? Just check on your own by selecting the area of your choice ;-) Regarding thickness we have to wait for PIOMAS modelled ice thickness to check hycoms values - I am looking forward to see that results.
Toggle Commented Jun 4, 2013 on New map on the block at Arctic Sea Ice
For example I tried to follow the divergence of ice due to the storm in the last days. (Divergence here: Rate of loss of ice concentration in selected area - that means assuming no melt but only flow out). Selected area: Large circle of 2.761 Mio sq km - about the CIA but away from coasts, because I did not want interference from leads opening in future. Postion of ellipse: 800 1450 and size: 600 600 date: ice fraction: 20.5. 98.71 % of the 2.761 Mio sq km circle 21.5. 98.71 22.5. 98.55 23.5. 98.27 24.5. 98.55 25.5. 98.43 26.5. 98.35 27.5. 97.65 28.5. 97.14 29.5. 97.88 30.5. 97.02 31.5. 97.06 1.6. 97.25 2.6. 97.25 3.6. 96.86 % of the 2.761 Mio sq km circle so between 20.5. and 3.6. we have a divergence (loss of SIA probably due to flow out of that circle) of about 50,000 sq km - not much for 2 weeks and I did expect more effect from the hycom concentration forecast.
Toggle Commented Jun 4, 2013 on New map on the block at Arctic Sea Ice
To compute SIA from that concentration maps is totally easy with gimp: * Select the area of interest * use the histogramm function (Menue: Colors -> information -> histogramm) * look up the "mean" value and devide it by 255 (=100% ice) to get the ice fraction * multiply by selected area (e.g. number of pixel from histogramm function times 3.125 km times 3.125 again (pixel area) It gives a bit more SIA than cryosphere today, probably because of better resolution. Pixel area is only correct at 70° latitude. And as Wipneus allready warned again: "these data are not officially released and work in-progress." Relative measurements are save and interesting anyway. All of this will not work with jpg or colored pictures - only linear grey scale and lossless bitmaps. If you have the black hole in your selection, choose lower level of histogramm >38 to avoid a wrong mean. This is a very nice and easy thing to compare SIA in areas of your personal interest from day to day. Just note the position and the size of your selection for comparisons over time and as reference for other poeple interested.
Toggle Commented Jun 4, 2013 on New map on the block at Arctic Sea Ice
"before you are absentmindly posting intended outcomes. " Outch! Please correct me if there is any error in the SIA calculations using Gimp (Short of the <6% error due to grid area).
Toggle Commented Jun 3, 2013 on If this is real... at Arctic Sea Ice
No further SIA change in the storm affected area again yesterday. A-Team - I guess you are also refering to your excercise in the other thread with the grey palette for numerical colours. Sorry I am such a noob with gimp - selection and histogramming works fine, but I could not figure out how to do most simplest things like "search and replace" of pixel colour values (instead of using that stupid bucket at every pixel) or putting a pixel value as function of pixel coordinates or some other function - let alone things like your "guillotine" or what. I will look in the manual today evening again - but right now I have the impression, that programming or lovely MatLab could do the job much easier for me. Simply because I have no artists background ;-) But I will not give up, because gimp could be a possibility also for non-Nerds.
Toggle Commented Jun 3, 2013 on If this is real... at Arctic Sea Ice
Chris, I got your point - of course divergence can not be seen in AMSR2. My point was - there is nearly no SIA lost in the wide area arround the storm (only 40-50k since 12 days) - so there is no source for transport of ice from the central CAB. Only arround Svalbard, but that region is not inside the 2.76 Mio km2 circle and I would not consider that as driven by the storm directly. It is more driven by A-Teams gear-wheel. If you compare 20th May and 1. June AMSR2 20. May: https://sites.google.com/site/apamsr2/home/pngcby32/Arc_20130520_res3.125_pyres.nc.png?attredirects=0 AMSR2 1. June: https://sites.google.com/site/apamsr2/home/pngcby32/Arc_20130601_res3.125_pyres.nc.png?attredirects=0 -> in the concentration map it looks much darker in the CAB after the storm, but it is only 40-50k less sea ice area. The only ice-movement increasing SIE is again around Svalbard into Barents. So - SIA-wise not much of an effect yet by the storm. But according to hycom concentration forecast something is still to come in the next days. I will try to get that - just to check the prediction.
Toggle Commented Jun 2, 2013 on If this is real... at Arctic Sea Ice
Chris, I can not find a significant indication for divergence in the AMSR2-pictures - a loss of 40-50k sq km SIA in ten days in the complete storm affected zone in the CAB is nothing to write home about. The 600-pixel circle spans also the circular shear region surrounding the spiral. I see two possible explanations: First - it takes some more days until the SIA is reduced there visible for the sensor. Maybe the clouds have to go or the relatively slow movement has to be completed or something like this to get a final measurement. Second possible explanation could be, that some of the water between the floes detected in visible and IR spectra is in fact only wetted ice by waves and spray? Albedo of water and sprayed wet ice is quite similar - immersion is the effect used in microscopy to get a clear look through a rough scattering surface. In anyway - water or wet ice will both drive the albedo-feedback and that will kick the CAB in the next weeks as you mentioned allready.
Toggle Commented Jun 2, 2013 on If this is real... at Arctic Sea Ice
BTW: Wipneus' usable version of the high res concentration pictures from Uni Hamburg are here (including 06. 01.): https://sites.google.com/site/apamsr2/home/pngcby32/
Toggle Commented Jun 2, 2013 on If this is real... at Arctic Sea Ice
SIA in Arctic Basin did not drop further yesterday. In the high res concentration pictures with (3.125 km)^2 grid I draw a circle (selection ellipse) in gimp from upper left position 800 1,450 with size 600 600 and (2.76 Mio sq km) and counted the mean ignoring values <38 (the black hole) and multiplied by area/255. Since 20th May the loss there is only about 40-50,000 sq km with "biggest" drops on 27-28. May. I thought effect of divergence and/or upstreaming would be maximal just when the storm moved and before it slowly damps. But the effect is either still not there or overlooked by the sensor. Werther, I like your "ridge count" - is is a good guide to the eye. If I understood wetterzentrale right, the European ridge is bending towards the Basin bringing Laplands heat (hottest place in Europe) to the Basin. Wheater is always a bit surprising - now it is surprisingly surprising and weather forecasts in the newspapers are a joke if you compare with yesterdays paper.
Toggle Commented Jun 2, 2013 on If this is real... at Arctic Sea Ice
I think it is OK to work wit the constant grid area - since it is a systematic error < 6% it will not increase by substraction like a statistical error. So the error in the SIA decrease of 46,000 sq km due to the storm is 2-3,000 sq km and quite similar to the dititalisation error of 1,000 sq km. Other errors like may be even larger (weather, melt ponds, ...) So I think, we can do nice things without correction. And I am tired of searching in the gimp manual for today anyway.
Toggle Commented Jun 1, 2013 on If this is real... at Arctic Sea Ice
I see, cell area is dependent on pixel number and should be used. I found a function "layer mode “Multiply”" which could do the trick before numerical integration via histogramm mean. But we would need a picture with the correction value as function of x and y (or in one color of the RGB-picture). I did not find a methode to use a function of x and y in gimp yet - really a strange thing for a programmer ;-) But there is still a lot to read and they call everything so differently (no math only coloring-words) - so there is still some hope.
Toggle Commented Jun 1, 2013 on If this is real... at Arctic Sea Ice
The effect of the storm on SIA was not very large up to now in the Arctic Basin. In a circle of 2.761 Mio sq km the SIA dropped from 2.725 Mio km2 (05/20) to 2.680 Mio km2(05/31) - that is a loss of 46,000 km2 only. Maybe the melting there is still to come? BTW - the number of pixels in the dark circle varies in the different pictures from Wipneus. A most likely value is between 2400-2500 pixels at a value of 37. The surplus number of pixel with value 127-128 is zero in the Basin - those are probably artifacts from clouds or coastal pixel further south.
Toggle Commented Jun 1, 2013 on If this is real... at Arctic Sea Ice
correction: To get SIA I put a selection box arround everything, used the histogram function ignoring black pixel to get average pixel value, _divided by 255_ and multiplicated that with number of non-black pixel and pixel area.
Toggle Commented Jun 1, 2013 on If this is real... at Arctic Sea Ice
Wipneus, You are right, a programming language is much more flexible - but that would be nerd-only. Gimp is n00b-proof (I just installed it yesterday and got the SIA without any look in a manual). And the Nerds may control gipm by scripts and write a plug-in for anything sophisticated. So gimp is a possible solution for A-Teams dream of "sea-ice investigation for everybody" and your picture-processing is the door to that dream. The NP-hole: I draw a selection box around it and counted the black pixels via information - histogram: 2051 pixels. I switched the lower boundary of the histogram to 1 to ignore black and got the average value of ice-concentration surrounding it: 249.7/255 So ice-are in the hole is: 249.7/255 x 3.125^2 x 2051=19,613 sq km. To ignore the white coastal pixels and the lakes I just painted them black. So at coasts with ice the error is still there. To get SIA I put a selection box arround everything, used the histogram function ignoring black pixel to get average pixel value and multiplicated that with number of non-black pixel and pixel area. I think after reading a bit in the manual to get a clue about A-Teams "mask-magic" and the scripting commands it should be easy for everybody to do this automatically for any region of interest and maybe also to produce the corresponding movies automatically.
Toggle Commented Jun 1, 2013 on If this is real... at Arctic Sea Ice
After correcting the satellite-hole (by using values surrounding it) and ignoring lakes and coastal white points the sea ice are from integrating Wipneaus high res picture Arc_20130530 is: 10.92 Mio sqkm (assuming pixel values linear proportional to area and pixel area constant). If someone would confirm that we could use the pictures easily e.g. to investigate the SIA-change produced by the cyclone in the basin in the next days.
Toggle Commented May 31, 2013 on If this is real... at Arctic Sea Ice
and why are there significant more pixel with value 128? (I removed the brown...)
Toggle Commented May 31, 2013 on If this is real... at Arctic Sea Ice
question @ Wipneus or A-Team I just tried some calculation using gimp - but I am not familiar to that (only Fortran...), so I am not sure what I got. From the picture Arc_20130530 I got an SIA of 10.97 Mio sq km (all ice) - that is a bit more than from cryosphere. OK - I got that hole in the middle and one extra lake in canada and some white pixels from the shore, that could explain the error. So my question is just to be sure: Is the pixel value linear to area in the pixel and are really all pixel 3.125^2 sq km or is there something to be corrected? Sorry for asking that stupid things here - but maybe it could help someone else to use these new pictures for something more useful, too.
Toggle Commented May 31, 2013 on If this is real... at Arctic Sea Ice