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crandles

I presumably we can take that "and are available via FTP" as the required permission to access the government computer.

Account Deleted

First impressions.

The main problem that needs a graphical program that can get the geographical coordinates and the thickness of ice on one card.

Each file is a single plane flight.

I tried to calculate the average thickness of the ice at some interval.

OIB_20120321_IDCSI2_ql.txt
The flight between Greenland and the North Pole
82-84 N 4.00 metres
85-87 N 3.03 metres
89 N 2.80 metres

OIB_20120319_IDCSI2_ql.txt
Flying over the Beaufort Sea
average thickness 1.86 metres

In general, very similar data to PIPS3
http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticictnnowcast.gif

JackTaylor

For those interested in running the data through a SpreadSheet, TEXT ( .*txt ) converted to .csv, .ods, and .xls are referenced at:

http://www.polk-nc.com/asi2012/index.html

`

Artful Dodger

NASA routinely makes Icebridge data available as a Google Earth .kmz file.

For example, here is the Oct 5, 2011 Antarctic data:
http://earthobservatory.nasa.gov/IOTD/view.php?id=76149

Arcticio

For a quick 'n' dirty approach it might help to export a xls thickness chart as bitmap and stretch/rotate it over the single 2km Arctic mosaic picture of the same day using the flight map.

Chris Reynolds

I've just managed to get the first file on that page into Excel. Took about 30 minutes, which is significant as some of those files are four times as large (IIRC).

Anyway. Due to the complexity and size of the data it's clear that analysing won't be a trivial matter. IMO it can't be done with Excel alone but if using that platform then macros would be the best tool.

On a cursory examination of the data....

It's amazing how much missing data there is in amongst ice that varies from 1m to 5m thick in short distances. I don't know why there is missing data. The great variability in thickness I suspect is due to areas that on NIS charts would be listed as MYI - i.e. the MYI ice is interspersed with thinner ice.

It is also worth bearing in mind that a lot of the thin ice is associated with thickness uncertainties of the same order as the thickness of the ice itself. I'm unsure how to interpret this - should we dismiss such thin ice?


Taking the first grid box of 20120314, this is lat 82 long 304, which puts it in the area poleward of Franz Josef Land. The average thickness is 2.187m, which is reasonable in light of other evidence. However there are some readings of 4 5 and 6 metres. These surprise me because in this region most of the ice should be FYI from Siberia through the transpolar drift.

Lat 85 Long 235 is in the region of the border of the Laptev Sea and Central Arctic. In this grid square ice is on average 3.65m thick, with some ice being over 10 metres thick and many readings of around 6m thick. The same arguments made above apply here.

Considering the HYCOM model plots, e.g.
http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticictn/nowcast/ictn2012032418_2012032800_035_arcticictn.001.gif
PIOMAS implied thickness (admittedly a coarse tool) Maslanik's drift age model, I wouldn't expect an average thickness of 3.65m in the second location above.

The ice bridge data tends more to the Cryosat results in suggesting thicker ice than the models seem to imply. Are the models suggesting a thinner pack than is really the case?

I should point out that in contrast to the above randomly picked boxes 80/205 has an average thickness of 1.289m. This is near the E Siberian Sea and is below the ~2m I'd expect for March.

Every piece of evidence I see raises new questions.

Account Deleted

"However there are some readings of 4 5 and 6 metres. These surprise me because in this region most of the ice should be FYI from Siberia through the transpolar drift."

This is not necessarily an old ice - possible hummocks (the region of strong compression)

Espen Olsen

It is amazing to watch that crack in the ice going all the way from the shores of Alaska to the North Eastern tip of Greenland (Cap Morris Jessup), must be a kind of record!

deconstruct

I just visualized the IceBridge flight data onto a NSIDC Polar Stereographic Grid:

http://www.luckyserv.de/climate/OperationIceBridge_March2012.png

The grid has a resolution of 12.5 km. Each grid cell displays the average of all data points that are located within that cell.

The OIB flight data have a much higher resolution, but because they just cover a very narrow band along the flight path, using a higher resolution wouldn't improve the image. And besides, I hadn't a higher resolution land mask at hand ;)

The uncertainty of the individual measurements is on average about 0.8 meters (median 0.65m). But because a grid cell in the image contains often more than hundred data points, this uncertainty should be reduced a good deal, at least if we assume that the difference to the real values is normally distributed. In this perspective, the lower resolution of the image is actually a good thing.

deconstruct

Account Deleted

deconstruct, nice job!

You used all the data files?

Neven

Wow, that's awesome, deconstruct! I'm updating this post with the image. Let me know if that's not okay with you, and I'll remove it.

deconstruct

@Arcticicelost80
Yes, I used all the files (13 files, from March 14th to April 2nd).

@Neven
No problem, you can post the image. And you could make me a "his", as I am no "her" ;)

Neven

No problem, you can post the image. And you could make me a "his", as I am no "her" ;)

OK, thanks. My wife called me a sexist today, so I wanted to prove her wrong. :-P

deconstruct

Because some people have wondered how the IceBridge data compare e.g. to models like HYCOM/CICE, I overlayed the Hycom model data (from March 20th) with the IceBridge measurements using the same thickness-coloring:

http://www.luckyserv.de/climate/OperationIceBridge_vs_HycomARC_March2012.png

The overlay is not 100% perfect, because I don't know what polar stereographic projection parameters they have used in the HYCOM image. But above 70°N, which covers all the flight paths, the match is sufficiently accurate, so that shouldn't be a problem.

My conclusion from a first glance at the differences is, that the IceBridge data suggest in most areas thinner ice than the Hycom model. Especially in the Beaufort Sea and in the area northwest of the Canadian Archipelago the IceBridge data show at least 1 meter thinner ice.
Good agreement is in the area near the pole and partly around Greenland.
Another thing that seems to emerge: The ice thickness around greenland is much more diverse and not so homogenous as the Hycom model shows, because IceBridge shows that there are small areas with substantially thicker or thiner ice.

Rob Dekker

deconstruct,
First of all, as Neven stated already : Wow.
Great presentation of the 2012 IceBridge data. Thank you very much !

If you can, could you please generate a similar image of the 2009 IceBridge data (same format) :
ftp://n4ftl01u.ecs.nasa.gov/SAN2/ICEBRIDGE_FTP/IDCSI2_CommunitySeaIce_v01/2009_GR_NASA/

There are fewer runs there, and they are from April (2009), thus one month off, but it would still be very interesting to see the differences between the 2009 and 2012 runs.

And/or, can you tell us how you did the projection on the map image, and via NSIDC Polar Stereographic Grid, so we won't have to bother you :o)

Regarding HYCOM, the model is known to vastly over-estimate ice thickness, probably because the intent of the model is to provide a 'worst-case' ice encounter for Navy vessels (both surface and submarine).

Daniel Bailey

Rob, having made navigational products for the US Navy (classified and unclassified), there is a fail-safe "cushion" typically built-in.

As Ed would say, "You are correct, sir!"

Chris Reynolds

My message "May 15, 2012 at 21:59"

Ignore the question "Are the models suggesting a thinner pack than is really the case?"

I got mixed up w.r.t. what direction longitude goes - the locations I mentioned need to be flipped 180 degrees. That's what comes of posting after too much overtime.

Derek

CT is back. Has that been mentioned?

Neven

Derek: yes, it has been. In the ASI Update 2 thread.

---

I have slept a bit last night, and I have to say again: It is so amazing what you did, deconstruct! This was exactly the thing I was hoping for when I put this out. Maybe I'm smarter than I think I am... ;-)

deconstruct
If you can, could you please generate a similar image of the 2009 IceBridge data (same format): ftp://n4ftl01u.ecs.nasa.gov/SAN2/ICEBRIDGE_FTP/IDCSI2_CommunitySeaIce_v01/2009_GR_NASA/
Of course, here it is:

http://www.luckyserv.de/climate/OperationIceBridge_April2009.png

There are however only 5 flights in the 2009 data set. The two flights at the end of April are the pink-purple triangle at the entrance of Fram Strait and the orange-red line west of Ellesmere Island. The other lines belong to the flights at the beginning of April, 3-4 weeks earlier.

At the entrance of the Fram Strait you can see, how quickly things can change regionally over the course of a month: At the beginning of April there seems to be substantially thinner ice, than at the end of April (see the intersection of the one flight with the triangle-like other flight).
I assume that this was caused by a ocean current/weather/wind/ situation that pressed the ice during April towards Fram Strait and there it jammed and piled up.

So I don't think that the data can be compared to the March 2012 data very well. The differences between the two may have nearly nothing to do with changes in the amount of Arctic ice, but simply with differences (caused by winds, currents etc) in how the ice was distributed at this particular point in time. Or put another way: With only two measurements with such a small coverage of the arctic, there is just to much noise here to learn anything from such a comparison.

What the IceBridge data are good for is to compare them to model data (PIOMAS, Hycom/CICE, etc) or other ice thickness measurements at the same points in time. Here we can learn things like if the models over/underestimate the thickness of the ice.

And/or, can you tell us how you did the projection on the map image, and via NSIDC Polar Stereographic Grid, so we won't have to bother you :o)
Well, I've written a small Java program that reads a NSIDC mask file in the Polar Stereographic Grid format (as described for example here: http://nsidc.org/data/polar_stereo/ps_grids.html) and projects the thickness data onto it using that same projection.
Chris Reynolds

Deconstruct,

"What the IceBridge data are good for is to compare them to model data (PIOMAS, Hycom/CICE, etc) or other ice thickness measurements at the same points in time."

Which was a major motivation for much of the recent ice bridge flights - validation of Cryosat. Hence more data recently.

Thanks for the graphics, it's saved me a lot of work.

Rob Dekker

Thanks Deconstruct, for visualizing the 2009 IceBridge data as well as 2012.
I also agree with your analysis. Especially in the ice-cruncher North of Greenland and Ellismere Island, the few streaks that IceBridge puts out are not enough to obtain statistical significance.

Interesting however is the flight over the Canadian Archipelago and right into the Beaufort. Ice is not as variable there, and it seems that between 2009 and 2012 some thinning occurred. But not sure if that is statistically significant.

Hopefully Cryosat will soon be able to provide data that is reliable enough without the hand-holding of IceBridge calibration, so we can enjoy 2D ice-thickness maps month-to-month, without having to rely on 1D streaks and fine people like you plotting that in an Arctic map.

Thanks again !

Stuart

Something showed up via an article at the Alaska Dispatch by Doug O'Harra.

http://www.agu.org/journals/gl/gl1208/2012GL051432/

Not specific to this season’s melt, but pretty germane to the underlying physical processes. Seams that it’s more than just ice volume involved. Article Figures at:

http://www.agu.org/journals/gl/gl1208/2012GL051432/figures.shtml#fig01

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