We have a pretty accurate 2D view of the Arctic sea ice, and some clues with regards to its third dimension: thickness. It's the thickness of the ice that determines the influence of atmospheric conditions on the ice pack, and is thus a crucial factor in the amount of sea ice that covers the Arctic Ocean during any given time, especially towards the end of the melting season. But also during the freezing season sea ice thickness plays an important role as an intermediary between sea surface and atmosphere. The thinner the ice is, the more heat and moisture can be transferred from one to the other, which in turn influences atmospheric patterns.
image on the top right, courtesy of NSIDC
The importance of accurate sea ice thickness measurements is not lost on the scientific community. We've had ICESat, we eagerly await the end of the calibration phase of the CryoSat-2 mission, and in the meantime another handy tool for measuring ice thickness has been devised by scientists from the University of Hamburg, using a passive microwave sensor aboard the ESA's Soil Moisture and Ocean Salinity (SMOS) satellite.
images retrieved from the SMOSIce wiki (with permission of L. Kaleschke)
The news was announced two months ago in an ESA press release, but has now been followed up by a research paper that has just been accepted for publication in Geophysical Research Letters: Kaleschke, L., X. Tian-Kunze, N. Maaß, M. Mäkynen, and M. Drusch (2012), Sea ice thickness retrieval from SMOS brightness temperatures during the Arctic freeze-up period.
From the abstract:
The Microwave Imaging Radiometer using Aperture Synthesis (MIRAS) on board the European Space Agency’s (ESA) Soil Moisture and Ocean Salinity (SMOS) mission for the first time measures globally Earth’s radiation at a frequency of 1.4 GHz (L-band). It had been hypothesized that L-band radiometry can be used to measure the sea ice thickness due to the large penetration depth in the sea ice medium. We demonstrate the potential of SMOS to derive the thickness of thin sea ice for the Arctic freeze-up period using a novel retrieval algorithm based on Level 1C brightness temperatures.
The SMOS ice thickness product is compared with an ice growth model and independent sea ice thickness estimates from MODIS thermal infrared imagery. The ice thickness derived from SMOS is highly consistent with the temporal development of the growth simulation and agrees with the ice thickness from MODIS images with 10 cm standard deviation. The results confirm that SMOS can be used to retrieve sea ice thickness up to half a meter under ideal cold conditions with surface air temperatures below -10◦ C and high-concentration sea ice coverage.
And from the conclusion:
[S]everal retrieval uncertainties remain that should be considered in future studies. Despite these uncertainties our analysis provides clear evidence for a maximum of the retrievable ice thickness [0.5 m]. SMOS obtains daily coverage of the polar regions with a resolution of about 35 km x 35 km which is suitable for several applications of a sea ice thickness product. We expect the greatest benefit during the cold freeze-up period in Autumn when extensive areas of thin sea ice control the ocean-atmosphere heat exchange, which is important for weather and climate, as well as for operational marine applications.
This quote from the above mentioned ESA press release from last December also explains the usefulness of this new technique:
The information on sea-ice thickness is complementing that delivered by ESA’s CryoSat. Carrying a radar altimeter, CryoSat uses a different method of measuring sea ice – the height of the ice protruding above the water.
SMOS can offer daily coverage over the polar seas, while CryoSat provides higher spatial-resolution data and orbits very close to poles, thereby giving extra coverage.
The puzzle is in the process of being solved.
I have not really been following the CryoSat. news very closely but since there are no sea ice thickness maps being released yet I am assuming that the system doesn't work well enough to derive thickness data. I am really hoping somebody closly in touch with the actual state of progress can tell me how wrong I am and let me know when I will be able to see some progress.
Posted by: RunInCircles | February 19, 2012 at 12:43
our analysis provides clear evidence for a maximum of the retrievable ice thickness [0.5 m]
That's a pretty honkingly important caveat!
Posted by: Peter Ellis | February 19, 2012 at 12:44
That is pretty neat.
Posted by: dorlomin | February 19, 2012 at 13:01
How well can we trust the CICE ice thickness maps? Compared to the same time last year, the ice now seems to be clearly thicker just north of the Canadian Archipelago, but clearly thinner on the Siberian side of the pole.
Posted by: AmbiValent | February 19, 2012 at 14:12
Even is limiter at 0.5 m, this is still a good step. More means better constrains on model, which will improve thickness estimation elsewhere in the pack.
Posted by: Yvan Dutil | February 19, 2012 at 14:36
>"How well can we trust the CICE ice thickness maps?"
Not sure if it is still the same, but IIRC the earlier product was believed to be an 'estimate danger to shipping' product that tended to overestimate thickness. Having said that, if it overestimates thickness, hopefully it does so consistently so comparing to last year should be useful:
http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticict/nowcast/ict2012021818_2012021700_035_arcticict.001.gif
http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticict/nowcast/ict2011021818_2011021900_035_arcticict.001.gif
Posted by: crandles | February 19, 2012 at 15:19
Thanks, those are the maps I meant. I was just curious whether it's possible to draw conclusions from those maps. Since PIOMAS estimates the current volume to be about the same as last year, a stronger concentration north of the Archipelago could mean that the Northern Sea Route opens earlier this year.
The North West Passage might open even though there is more ice on the Canadian side, since the channels inside the Archipelago appear to have less ice than last year.
Also, if there is more open water, it could also accelerate melting due to more sunlight getting absorbed by the seas.
Of course, everything depends on the actual weather in the Arctic Circle this year.
Posted by: AmbiValent | February 19, 2012 at 18:04
Regarding CryoSat: Its measurement approach is different enough from IceSat and previous methods that CryoSat may be most comparable with itself. That is, well enough suited to tracking change over the period of its own observation, but less suited for extending the time series generated by earlier, less processing-intensive methods.
Posted by: L. Hamilton | February 19, 2012 at 22:52
Does anyone know of any research papers or other information that identifies the role of different ages of ice loss in the volume loss shown by PIOMAS?
Posted by: Chris Reynolds | February 20, 2012 at 20:15
Very fine information. Even with validity limited to less than .5m, there is now one gauge more to calibrate PIOMAS and other models and narrow error bars.
I too was wondering why there is (at least to my knowledge) virtually no thickness data coming out of the CryoSat project.
Posted by: Dominik Lenné | February 21, 2012 at 01:55
On the sidebar you can find an arctic sea ice news item that some classified submarine measurements are also becoming available:
http://www.bbc.co.uk/news/science-environment-17129988
Posted by: Wipneus | February 23, 2012 at 10:48
Thanks, Wipneus. Now if only the Russians would do something similar--but I'm not holding my breath on that one!
Posted by: Kevin McKinney | February 23, 2012 at 16:32
Some UK submarine data has been available for scientists, indeed Wadhams reportedly has an open invitation on UK subs going under the sea-ice. However the available UK data has, to date, been excluded from studies that use the pre-existing US Navy Data Release Area data. This is because of doubts over the consistency of the data.
I think this issue is mentioned in the Schweiger paper on PIOMAS uncertainty.
Posted by: Chris Reynolds | February 23, 2012 at 20:29
No images today from Aqua orbit swathe or mosaic.
As the Terra / Aqua satellites are well past their projected life I am wondering: is this a data-handling glitch at Lance Modis, or is it a glitch in the satellite?
Time will tell.
Here in Kent it is exceedingly warm - the warmest February day that I can remember. William Hill is offering 8 to 1 that this year will see a new highest ever temperature. I'd go for that if I was a gambler.
Posted by: logicman | February 25, 2012 at 17:59