« Area vs Extent: Graphs | Main | Run, rabbit, run »


Feed You can follow this conversation by subscribing to the comment feed for this post.

Nick Barnes

Off-topic: Check out today's MODIS of the NWP and the northern archipelago:
There's a lot of cloud, but some detail is visible through it. Blink with this one from the end of June to identify the coastlines:

There is snow on many of the islands, but there is also open water. There's a big swathe of it south of Ellef Ringnes island, and a narrower swathe of it all around the western side of that island right up to Cape Isacsen on the Arctic Ocean. Some patches of open water near some of the other islands.


I noticed it too one minute ago, Nick. I can't wait for those clouds to move aside again.


ECMWF is forecasting some big highs over the Canadian Archipelago 5 days from now. If this comes about, we will have our seat right next to the pitch to watch the game unfold.

Unisys doesn't agree, I think.

Jim Dowling, where are you?


USCGC Healy just entered the arctic ocean http://www.sailwx.info/shiptrack/shipposition.phtml?call=NEPP
on the way to a very ambitious and long lasting cruise to map the seafloor in the Canada basin http://continentalshelf.gov/missions/10arctic/welcome.html and there probably encounter the last surviving old ice of the entire arctic ocean.


@ siili
MODIS actually have some good holes through the clouds, showing ice streatching almost all the way from Wrangel to Alaska, not showing on Bremen...

I found the same discrepancy between the NOAA analysis for Alaska and the maps from the Canadian ice service here and here , and Uni Bremen sattelite images . Does anybody know what these maps are based on?


From what i remember the biggest difference is the purpose of the maps, Bremen and others like that are primarily made out of an effort to understand the science of the arctic system, they are, once the code is written, running automatic without human interference and gives maps based on e.g. a fixed 15% concentration limit using the chsen algoritm and detector.

The Iceservices has a very different mission, to support shipping and other professional operation, and then it is very important not to miss any ice which might be a problem to any vessel venturing into ice infested waters. So they use all detectors available, microwaves passive and active from all satellites,optical, ship reports, the lot. And they have very skilled people looking at all this data before constructing the charts.

So no wonder they show more ice.


A short background to remote sensing of ice using passive microwaves, used by e.g. Bremen, JAXA, and NSIDC.

All objects radiate at different wavelengths, mainly dependent on the temperature of the object, the mainly in the optical, the earth mainly in the infrared. In the microwave wavelength range, how much an object emitts is not mainly due to the temperature of the object but instead on the texture,or roughness of it. Smooth surfaces like calm water emitts little mircowaves, rough surfaces like stormy water a lot, and stuff inbetween like land and ice emitts inbetween. In the image this is mapped to shades of gray. There are also other tricks like polarisation state, but let's save that for now.

I have not found many basic images from mircowaves, but one example showing similar effects is from a variant tecniqe, using ACTIVE micowaves i.e. RADAR

There are some "stripes" in the Beaufort that might be from cloud effects. Otherwise the brokenup state of the ice is very clearly seen all the way in to the hole at the pole caused by the orbital plane of the satellite. Also note the filamentary ice close to Bering strait and compare it to visual MODIS images.

Due to the use of Synthetic Aperture Radar (SAR) , the resolution in much better than passive detectors, which usually have 25km, in this image it's 1km in the original data and in the image probably limited by the pixelsize.


Thanks Siili, great picture!

The comments to this entry are closed.