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danp

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Clear-sky 8-day Arctic mosaic
« on: July 17, 2013, 02:47:47 AM »
MODIS Terra & Aqua produce a variety of processed higher-level data products, almost all of which are then projected onto a sinusoidal tiled grid.  I had mostly been ignoring these products since the sinusoidal grid is almost unusably distorted through most of the Arctic, until I realized that the projection is area-preserving and ideally invertible.  In practice it still took some work to get reasonable results, but here's one.

The data are MOD09A1, Terra 8-day "clear-sky" tiles.  (See https://lpdaac.usgs.gov/products/modis_products_table for the full list of MODIS products). NASA takes all of its observations every 8 days and produces a best-view mosaic that has unsurprisingly exceeded my best amateur efforts.  They also do daily versions that of course have more clouds but are more up-to-date.   I reprojected to polar stereographic and produced the mosaic using the MODIS reprojection tool, and then combined bands 1, 4, 3 for RGB.  I could produce mosaics of any other band combination as well.

This particular mosaic covers days 185-193. (July 5-12).  Attached is a thumbnail image; the link is to a full-resolution zoomable version, 500m resolution.  NASA's projection from rectangular swath to sinusoidal followed by my undoing of that projection does result in some degradation of resolution, but it is not too terrible, and the procedure is much simpler than direct processing of the swath data has been.  (It also requires far less data downloading).

https://googledrive.com/host/0B2HXhBb-Jqf6NEt6Q3A4dnpzUms/

Neven

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Re: Clear-sky 8-day Arctic mosaic
« Reply #1 on: July 17, 2013, 07:07:31 AM »
Wow, impressive, danp!

Last year I wrote a series of posts called Peeking through the clouds. These revolved around MODIS Composites that are released every 7 days by Environment Canada. They make a True-Colour Composite image as well as a False-Colour Composite image.

One commenter called dabize would send me cleaned up - or "declouded" - versions of those MODIS False-Colour composite images.
« Last Edit: July 17, 2013, 07:15:59 AM by Neven »
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ChrisReynolds

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Re: Clear-sky 8-day Arctic mosaic
« Reply #2 on: July 17, 2013, 07:23:56 AM »
Thanks, very good.

anonymous

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Re: Clear-sky 8-day Arctic mosaic
« Reply #3 on: July 17, 2013, 12:20:12 PM »
The preview looks great, unfortunately the map interface doesn't load openlayers.js from http. Might be a Chrome issue.

Wipneus

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Re: Clear-sky 8-day Arctic mosaic
« Reply #4 on: July 17, 2013, 12:56:31 PM »
The preview looks great, unfortunately the map interface doesn't load openlayers.js from http. Might be a Chrome issue.

Same here, a little shield in the url bar appears. Clicking that gives an option to proceed at your own risk.

roman_01

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Re: Clear-sky 8-day Arctic mosaic
« Reply #5 on: July 17, 2013, 01:29:40 PM »
In Firefox works perfectly...Mosaic looks great, wow..

danp

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Re: Clear-sky 8-day Arctic mosaic
« Reply #6 on: July 17, 2013, 05:58:18 PM »
The preview looks great, unfortunately the map interface doesn't load openlayers.js from http. Might be a Chrome issue.

Same here, a little shield in the url bar appears. Clicking that gives an option to proceed at your own risk.

Hmm, it might be a hosting issue with http vs https as I haven't tried directly hosting something on google drive before.  It was the easiest free option I could think of for a premade folder structure as google sites makes it very painful to recreate that.

danp

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Re: Clear-sky 8-day Arctic mosaic
« Reply #7 on: July 17, 2013, 06:15:18 PM »
Wow, impressive, danp!

Last year I wrote a series of posts called Peeking through the clouds. These revolved around MODIS Composites that are released every 7 days by Environment Canada. They make a True-Colour Composite image as well as a False-Colour Composite image.

One commenter called dabize would send me cleaned up - or "declouded" - versions of those MODIS False-Colour composite images.

That's right - I had completely forgotten about those posts and this data source.  It is basically the same thing as this 8-day mosaic although I don't think they've done as well with preserving the data's dynamic range.  I should probably focus on the daily mosaics then.  Unfortunately I had miscalculated the amount of the data download for the daily composite tiles to produce the mosaics: at 12 GB or so a day it seems to be more than downloading all the swaths that produced the composite, which I don't understand.  Perhaps I'll go back to my original DIY declouding technique since downloading all the swaths also allows animations. 

My own technique for declouding is more primitive than NASA's.  Somehow they manage to average all data, weighted by the estimated cloud-free quality per pixel.  I instead just pick out the most cloud-free pixel from among all swaths that covered that pixel.  I use NASA's level 2 cloud mask product, which has 48 bits corresponding to various tests based on IR channels, temperature measurements, etc.  I looked through all of these tests and identified 5 that seemed useful discriminators in the Arctic, ranked them, and used the combination to produce a numerical score for every pixel.  Then whichever swath has the highest pixel score in that calculation gets used.  Unfortunately this method still requires a fair bit of manual oversight in the end, as some swaths turn out to add a lot of scattered noise to mess up the picture but no real improvement.

ChrisReynolds

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Re: Clear-sky 8-day Arctic mosaic
« Reply #8 on: July 17, 2013, 07:09:23 PM »
Dan,

Good to see more people using Google Docs for massive images. It's a great interface I've not used since winter - and should use more!

For myself, the image viewer works fine in IE10 and Chrome. But in both I have to click to run unsafe content.

Vergent

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Re: Clear-sky 8-day Arctic mosaic
« Reply #9 on: July 17, 2013, 09:27:07 PM »
Dan,

That is the best visible spectrum image of the arctic ice ever! Thanks so much for that.

Verg

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Re: Clear-sky 8-day Arctic mosaic
« Reply #10 on: July 17, 2013, 11:22:52 PM »
The eastern CAB is the 600 lb gorilla in the room.

Verg

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Re: Clear-sky 8-day Arctic mosaic
« Reply #11 on: July 18, 2013, 05:44:02 AM »
What direction is east from the pole?   ;)
Any sufficiently advanced technology is indistinguishable from magic.

Artful Dodger

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Re: Clear-sky 8-day Arctic mosaic
« Reply #12 on: July 18, 2013, 08:44:09 AM »
What direction is east from the pole?   ;)

The Eastern hemisphere: 0 E to 180 E, including Russia and Northern Europe.  :P
Cheers!
Lodger

danp

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Re: Clear-sky 8-day Arctic mosaic
« Reply #13 on: July 24, 2013, 08:10:46 PM »
NASA has new 8-day averaged tiles out, so I produced a new mosaic!  I've attached a preview comparison with the earlier one.  Note that while NASA's averaging algorithm is making an attempt to pick out clear pixels, consistently cloudy areas will still wind up with smeared clouds in the result, which makes it a bit tough to judge the ice condition in the center of the pack from the overview (it's easier in the full size).  For example I doubt the amount of open water in the east Arctic basin has reduced; it's just that there was more consistent cloud there in the second period.  I will be producing mosaics in other band combinations that should clarify this kind of issue.

artic.io has graciously offered host the full-sized images using the excellent zooming interface already in place there, so one of us will post a link to that shortly.

1st frame: July 4-11
2nd frame: July 12-19          (open attachment to play animation)
« Last Edit: July 24, 2013, 08:27:35 PM by danp »

Espen

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Re: Clear-sky 8-day Arctic mosaic
« Reply #14 on: July 24, 2013, 08:21:38 PM »
Dan;

Great work!!! ;)
Have a ice day!

danp

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Re: Clear-sky 8-day Arctic mosaic
« Reply #15 on: July 24, 2013, 08:22:38 PM »
Apparently animated gifs don't play in the previews here (click to open the attachment to play it).  If you just want to see an overview of the latest image, here it is:

anonymous

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Re: Clear-sky 8-day Arctic mosaic
« Reply #16 on: July 24, 2013, 10:01:43 PM »
I've made both cloud free mosaic zooms accessible via these clickable images:


Most striking change to me is how quickly sea ice retreated from Franz-Josef-Islands.

Many thanks to DanP, he must have spend a hell of a lot time fighting NASA's projections, distributions systems, enormous file sizes and complex scientific formats. I hope this is just a kick-off to a series of new insights into the Arctic's ice-pack with high res cloud free images. Seeing the ice pack scattered in true color and not hidden by clouds is actually very much needed in theses times.

Neven

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Re: Clear-sky 8-day Arctic mosaic
« Reply #17 on: July 24, 2013, 11:01:32 PM »
Wow, this is so effing awesome! Sorry for the rudeness.
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danp

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Re: Clear-sky 8-day Arctic mosaic
« Reply #18 on: July 25, 2013, 12:18:20 AM »
Thanks Neven! 

To back up what I said above about estimating the amount of open water in the east central arctic, here are snapshots of the band 7-2-1 mosaics for the same time periods.  You can see the mosaics are not as cloud-free as the visible 1-4-3 combination make them look, since most of the clouds are over white ice.


anonymous

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Re: Clear-sky 8-day Arctic mosaic
« Reply #19 on: July 25, 2013, 12:32:44 AM »
Great, this band selection makes clear how clouds and surface melting are related. Although, I miss phytoplancton blooms a bit :)

Edith added a link: http://www.arctic.io/zoom/G3ipI/0.5;0.5;1.1/2013-185-721
« Last Edit: July 25, 2013, 01:07:28 AM by arcticio »

danp

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Re: Clear-sky 8-day Arctic mosaic
« Reply #20 on: July 25, 2013, 12:50:45 AM »
By the way, anyone who wants to download full-size single-images of these mosaics and the ones I will be producing in the future can find them in the folder at https://googledrive.com/host/0B2HXhBb-Jqf6WlZ1NTN1WHd1amM/

They are about 4900x4900 pixels and 9 MB JPGs.  They are named by day # of first day in the mosaic, and band combination.

Vergent

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Re: Clear-sky 8-day Arctic mosaic
« Reply #21 on: July 25, 2013, 01:11:23 AM »
DanP,

Thanks so much for this.

arctic.io,

Thanks for the zoom. Split zoom in the offing?

Neven,

This is a world class arctic sea ice resource, I think it should be pegged. you can probably unpeg "vote with your guts", no one  has posted on it since June 12.

Vergent

anonymous

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Re: Clear-sky 8-day Arctic mosaic
« Reply #22 on: July 25, 2013, 02:02:35 AM »
arctic.io, Thanks for the zoom. Split zoom in the offing?

Sure, expect something to happen next weekend... ::)

Vergent

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Re: Clear-sky 8-day Arctic mosaic
« Reply #23 on: July 28, 2013, 08:10:16 PM »
arctic.io, Thanks for the zoom. Split zoom in the offing?

Sure, expect something to happen next weekend... ::)

Okay, I am expecting.

V

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Re: Clear-sky 8-day Arctic mosaic
« Reply #24 on: July 28, 2013, 09:19:54 PM »
arctic.io, Thanks for the zoom. Split zoom in the offing?
Sure, expect something to happen next weekend... ::)
Okay, I am expecting.
Lol, now you are on top of the list of beta testers http://www.arctic.io/clear-sky-zoom/  ;D

Vergent

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Re: Clear-sky 8-day Arctic mosaic
« Reply #25 on: July 29, 2013, 01:48:11 AM »
arcticio,

Wonderful! No hunting for combinations of days that are clear in the same spot.

Thank You,

Vergent

edit: and of course thanks to DanP

Vergent

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Re: Clear-sky 8-day Arctic mosaic
« Reply #26 on: July 29, 2013, 01:50:30 AM »
arcticio,

how do you image select for the left hand screen?

V

Neven

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Re: Clear-sky 8-day Arctic mosaic
« Reply #27 on: July 29, 2013, 09:45:18 AM »
I think the next Mosaic is going to be truly spectacular. There are holes all over the place.
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anonymous

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Re: Clear-sky 8-day Arctic mosaic
« Reply #28 on: July 29, 2013, 09:49:06 AM »
how do you image select for the left hand screen?

Thanks for confirming right hand works. That selector will appear on the other side very soon too. In the meantime try to alter the image code of the url. Hint: click once on the permalink to get the idea, it's year.day.bands

danp

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Re: Clear-sky 8-day Arctic mosaic
« Reply #29 on: July 29, 2013, 10:26:22 AM »
Funky interface but I think I'm getting the hang of it!  Great job arcticio and thank you so much for your work.  Now it's definitely my turn to get my scripts working to start adding in some more mosaics from the past for comparison.

Where should I start?  I was thinking of continuing back through the season to say June, and then starting to add in date-comparable mosaics from past years.  Any particular requests?  I'll probably stick to bands 143 and 721 as my current method only has me downloading the first 7 bands (the downloads are heavy enough as it is), and within that range I didn't find a band combination particularly superior to 721 for the ice right now.

P.S.  stay tuned ... there may be daily mosaics on the horizon!

Artful Dodger

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Re: Clear-sky 8-day Arctic mosaic
« Reply #30 on: July 29, 2013, 10:31:04 AM »
Any particular requests?
Hi Dan,

Why yes, since you ask ;)

How about the period covering GAC2012? - Aug 02 to Aug 08, 2012.

And maybe +/- 7 days to get the coverage? An animation would of course be the holy grail for ice-watchers  8)
Cheers!
Lodger

anonymous

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Re: Clear-sky 8-day Arctic mosaic
« Reply #31 on: July 29, 2013, 10:38:27 AM »
I think the next Mosaic is going to be truly spectacular. There are holes all over the place.

These holes attract clouds like honey pots bears, grrr.

Vergent

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Re: Clear-sky 8-day Arctic mosaic
« Reply #32 on: July 29, 2013, 04:05:43 PM »
how do you image select for the left hand screen?

Thanks for confirming right hand works. That selector will appear on the other side very soon too. In the meantime try to alter the image code of the url. Hint: click once on the permalink to get the idea, it's year.day.bands
Got it, now I can compair the other bands.

V

edit: BTW the revolving globes image select tool is cooler than a Slurpee

https://www.slurpee.com/

« Last Edit: July 29, 2013, 04:15:56 PM by Vergent »

anonymous

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Re: Clear-sky 8-day Arctic mosaic
« Reply #33 on: July 29, 2013, 04:23:59 PM »
> BTW the revolving globes image select tool is cooler than a Slurpee

Sure, b/c it is not restricted to US residents.

Vergent

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Re: Clear-sky 8-day Arctic mosaic
« Reply #34 on: July 29, 2013, 04:48:37 PM »
> BTW the revolving globes image select tool is cooler than a Slurpee

Sure, b/c it is not restricted to US residents.

That's why I put in the link. I'm sure you have a brain freeze drink, they just call it something different.

But, since you have appointed me Beta tester, might I suggest a Lat/Long read out for the pointer. That would make it much easier to point out a feature?

Vergent
« Last Edit: July 29, 2013, 05:02:34 PM by Vergent »

anonymous

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Re: Clear-sky 8-day Arctic mosaic
« Reply #35 on: July 29, 2013, 06:00:43 PM »
But, since you have appointed me Beta tester, might I suggest a Lat/Long read out for the pointer.

No, that's project consultant and no proposal queue has been allocated for this post. :) However, it would involve a math degree, which I lack, but Dan might have a formula at hand taking pixel coordinates outputting Earth coordinates.

anonymous

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Re: Clear-sky 8-day Arctic mosaic
« Reply #36 on: July 29, 2013, 06:41:18 PM »
Just uploaded left and right hand Super-Slurpee featuring Petermann glacier pieces. Is it obvious how to deal with the controls?

URL: http://www.arctic.io/clear-sky-zoom/2013.192.721;2013.200.143/0.297174691;0.558441549;15.704180064/Petermann

TerryM

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Re: Clear-sky 8-day Arctic mosaic
« Reply #37 on: July 29, 2013, 07:16:01 PM »
Arctic.io


Would it be possible to do a split with the declouded version on one side & the daily split on the other?


I often skip back to an uncloudy image on one side when trying to identify a feature through the clouds on the other and this works very well, but always having a clear version on one side might help in some circumstances.


I've been a huge fan, especially since the split zoom was released.
Keep up your amazing work.
Terry

anonymous

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Re: Clear-sky 8-day Arctic mosaic
« Reply #38 on: July 29, 2013, 07:30:14 PM »
> Would it be possible to do a split with the declouded version on one side & the daily split on the other?

Terry, I'm constantly thinking on how to combine the single zoom, split-zoom and the new clear sky zoom into one thing, I'm sure it is possible. But the interface gives me headaches, the 8 day images do not work with a calendar (can't map weeks onto days) and the single day do not work with the new image flow (too many images, hundreds of them).

Until something enlightens me I propose using two browser tabs.

TerryM

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Re: Clear-sky 8-day Arctic mosaic
« Reply #39 on: July 29, 2013, 07:54:42 PM »
Arctic.io


No problem. I had no idea if it was a trivial matter or one that would require rethinking the whole system. Running one split to a clear day is easy to do.


Terry

danp

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Re: Clear-sky 8-day Arctic mosaic
« Reply #40 on: August 02, 2013, 04:18:25 AM »
The latest mosaics are processed, day 201-208.  This one was the cloudiest one yet, so if you're hole-hunting the 721 image is particularly useful for avoiding being fooled by persistent clouds.

Here's an animation of the three 7-2-1 mosaics:



You can see some big changes in the East siberian sea and holes opening up in the west central Arctic.

I also attached overviews of the latest 143 and 721 mosaics.  As always you can find the full-size versions at https://googledrive.com/host/0B2HXhBb-Jqf6WlZ1NTN1WHd1amM

and they will be up in the split zoom at arcticio soon.

Jmo

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Re: Clear-sky 8-day Arctic mosaic
« Reply #41 on: August 02, 2013, 04:42:01 AM »
Great stuff as usual danp!  Thank you for the work you put into these updates. :)

Vergent

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Re: Clear-sky 8-day Arctic mosaic
« Reply #42 on: August 02, 2013, 05:25:08 AM »
DanP,

Thanks for that. Eastern CAB not ice free on Aug 1(as I predicted(my bad)). But it will be soon.

Vergent

danp

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Re: Clear-sky 8-day Arctic mosaic
« Reply #43 on: August 02, 2013, 06:14:59 AM »
DanP,

Thanks for that. Eastern CAB not ice free on Aug 1(as I predicted(my bad)). But it will be soon.

Vergent

Cheer up!  The mosaic only covers July 20-27 :)  (there is always a lag before the 8-day tiles are uploaded, and it was a little longer this time).  And since the algorithm picks the clearest tile with no preference for recentness, the average date will be in the middle of that period. So really the next mosaic will have an effective center date around Aug. 1st.

But it's true that the up-to-date MODIS images also show that ice sticking around stubbornly.  Heck, being wrong (and remembering) is good - I've mostly been too confused this year even to get that far.

Vergent

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Re: Clear-sky 8-day Arctic mosaic
« Reply #44 on: August 02, 2013, 09:40:34 PM »
http://www.whoi.edu/page/preview.do?pid=111896

ITP-57 has been measuring above freezing temperatures for the last 50 days. The bottom melt must be horrific. Its just a matter of time. If it melts out in the next 10 days or so, I will not be embarrassed, that would only be a 20% error in time, and no real error in result. I think this ice must have been thicker than PIOMAS said. Although, the conditions have been unfavorable for melting.

Vergent


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Re: Clear-sky 8-day Arctic mosaic
« Reply #45 on: August 10, 2013, 03:13:55 AM »
Day 209 (i.e., days 209-216) mosaic is up.  Here's a comparison with the previous mosaic.  Note that due to the usual time lag the most recent storm hadn't started up yet by the end date of the latest mosaic.



I also uploaded 1-4-3 and 7-2-1 mosaics going all the way back to day 145 of this year.
( https://googledrive.com/host/0B2HXhBb-Jqf6WlZ1NTN1WHd1amM )

Here's an animation including all of these mosaics, which started May 25th.


Attached are thumbnails of the most recent mosaics as usual.

Vergent

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Re: Clear-sky 8-day Arctic mosaic
« Reply #46 on: August 10, 2013, 06:08:25 AM »
Dan,

Thanks so much for that.

Vergent

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Re: Clear-sky 8-day Arctic mosaic
« Reply #47 on: August 17, 2013, 08:31:21 AM »
Hot off the presses, our octodaily images return with the day 217 mosaic.  Huge changes are visible since the previous mosaic, with the wide stretches of low concentration straight through the pole finally showing up.  Here's the channel 7-2-1 blink comparison with day 209, and the 1-4-3 and 7-2-1 current thumbnails.  As always full-size versions at

https://googledrive.com/host/0B2HXhBb-Jqf6WlZ1NTN1WHd1amM/





Pmt111500

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Re: Clear-sky 8-day Arctic mosaic
« Reply #48 on: August 17, 2013, 09:53:52 AM »
Is it ok to share the image?

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« Last Edit: August 17, 2013, 04:13:50 PM by Vergent »