Walt sent me this essay unsolicited, and I think it is very useful for establishing some baseline techniques. There’s more useful information on techniques here than in the entire Catlin Arctic Survey website. UPDATE, a response has been posted at the end of the article. – Anthony
Dr. Walt Meier
There have been several recent posts on sea ice thickness, particularly in regards to the Catlin expedition. I don’t have any direct connection to Catlin and in my research focus, I don’t anticipate using the Catlin data. I’m not responding to defend them or their methods. Thus, I can’t address details of their operation. However, from reading the posts and comments it seems like some basics on how sea ice thickness is estimated might be of interest.
Sea ice floats in the ocean. Because sea ice is a lower density than unfrozen water, it floats and a portion (~10-15% depending on density) rises above the water line, while most of the ice (~85-90%) is below the surface. The part of the ice cover above the water line is called the “freeboard”; the portion below is called the “draft”. The sum of the freeboard and the draft is the total ice thickness. There may or may not be snow on top of the ice which can add to the “snow+ice freeboard” and the “snow+ice thickness”.
A variety of techniques have been developed to obtain information about sea ice thickness. Most of these methods don’t actually directly measure thickness but estimate thickness from a related measurement. Here are some examples:
Upward Looking Sonar: Mounted on a submarine or on the ocean floor, these instruments measure the return of sound waves bouncing off the bottom of the sea ice. They measure the sea ice draft from underneath the ice. From this draft measurement, the thickness can be derived with knowledge of the ice and water density and the snow cover.
Altimeter: Compared to sonar, altimeter measure the opposite side of the ice. They measure the freeboard from above the ice, from which the total thickness is derived. The NASA ICESat is a laser altimeter, which actually measures the snow+ice freeboard, so knowing something about the snow cover is particularly important (http://www.nasa.gov/images/content/324868main_kwokfig2_full.jpg). Radar altimeters are also often used (including the European Cryosat-2 scheduled to be launched later this year); these penetrate through the snow and thus measure the ice freeboard. ICESat can take a lot of measurements over a large region of the Arctic, but there are limitations, which are discussed below. Altimeters can also be flown on airborne platforms.
Ground radar: This carried on or near the surface and sends out a radar pulse that echoes off the ice-water boundary. Thus it is an estimate of the total ice+snow thickness.
Drill holes: This is the simplest way to obtain ice thickness and it is the only direct measurement of ice thickness – drill a hole and stick measuring tape through it and you have the thickness (whether it is in units of meters, feet, or smoots [http://en.wikipedia.org/wiki/Smoot]). A variant of drill holes are the ice mass balance buoys that Steven Goddard wrote about – drill a hole and put in instrumentation to estimate thickness automatically over time.
There are errors associated with any estimate, but the errors tend to be higher the farther one is away from a direct measurement. For example, for ICESat, you need to know very precisely: (1) the altitude of the satellite above the surface, (2) the ocean surface topography [sea level isn’t constant], (3) the density of the ice and water, and (4) the density and height of the snow cover. All four of these are challenges, though by far the biggest one is #4. There just isn’t a lot of information about snow. ICESat has already provided valuable information about sea ice thickness over large regions of the Arctic and more results will be forthcoming. However, the goal is to continue to improve these estimates to make them even more useful.
This is where surface measurements, radar and drill holes are particularly valuable because they provide “ground truth” – of both ice and snow thickness. The problem with these ground measurements is that it is difficult to obtain a large number of them over a broad area. And this is particularly important for sea ice thickness, which can vary considerably over short distances. This is a limitation of the ice mass balance buoys. There are only a few within the entire Arctic and they measure thickness on a single floe. Even in the immediate vicinity, ice thickness could be quite different than that being measured by the buoy. Thus, while the buoys provide an excellent measurement of thickness at a point through the seasons, they do not provide good information on the large-scale spatial distribution of ice thickness.
Ideally, we’d send a few thousand people out to the Arctic and drill thousands of holes and get good sampling of thickness, but this is just not possible. Even putting out more than a few autonomous buoys are impractical because of the cost of the buoys and the fact that they only last a few years (the ice melts and the buoys are lost, though people are looking about buoys that can float and could potentially be recovered and recycled).
This is where the Catlin expedition can be particularly valuable. To have a group out on the ice taking direct measurements of thickness across a relatively large region (compared to most field expeditions) of the Arctic is something that has only rarely, if ever, been done before. It is unfortunate that the radar may not have worked as well as hoped, but that is the nature of field work, especially in harsh polar environments – things almost never go according to plan. The radar would essentially provide a continuous transect of thickness estimates over several hundred kilometers. However, the drill hole measurements taken regularly over the route will still likely be valuable.
It is also unfortunate that they are not likely to get as much data from multiyear ice as hoped because that is of greater scientific interest, but any ground truth estimates can help improve data from satellites like ICESat is useful. Their planned route looked like it would’ve taken them over ice of varied ages, but the older ice moved out of the area over the winter and, as Steven Goddard showed comparing their position with the ice age data on NSIDC’s web page, they started squarely in first-year ice. Generally, logistics for an expedition need to be planned several months in advance, long before anyone can know how and where precisely the ice will move. Like many scientific expeditions, it seems like they won’t get as much data as hoped, but ground data from the ice is so rare that every little bit helps.
As a final note, since it seems the measuring tape used by Catlin is of great interest, I’ll end with a bit of information on that. Basically, it is simply a measuring tape, but with a collapsible metal flange at the end of the tape. The weight pulls the tape down through the hole to the bottom of the ice. Then you pull the tape taught and the flange opens and catches on the bottom of the ice. You make your measurement, then pull hard on the tape and the flange collapses and you can pull it up through the drill hole. Since such tapes with flanges are relatively specialized, there aren’t many places to get one. One place is Kovacs Ice Drilling Equipment
http://www.kovacsicedrillingequipment.com/ice_thickness_gauge.html
NSIDC has a gauge from Kovacs and it has units of meters and feet, on opposite sides of the tape. I would guess that the Catlin tape is similar, but I don’t want to jump to conclusions.
Response to Dr. Meier by Steven Goddard.
First, I want to thank Dr. Meier for his candid explanation of how Catlin landed on first year ice, and how ice is measured. As always, he has treated our concerns seriously and that is very much appreciated.
Dr. Meier said that the ice “can vary considerably over short distances” and the Catlin web site has said “the team systematically seeks out flatter ice.” That implies to me that there is a geographical bias to the data which makes the entire data set suspect. (That might be analogous to having a temperature set where a disproportionate percentage of the thermometers were located in Urban Heat Islands.) If I were traveling across the Arctic pulling a 100Kg sledge in -40 degree weather, I would certainly seek out the flattest ice, as they have done.
The Catlin team has reported “Snow thickness, measured by the team during the first 2 weeks of March, shows an average snow depth of around 11 centimeters. Since then the average has risen to around 16cm.” Four to six inches of snow hardly sounds like a serious problem in estimating ice thickness in metres. They also said “March snow depths in this area should be 32‐34 cm on multi‐year ice.” If snow thickness is less than expected, does that imply that the satellites may be slightly underestimating the thickness of the ice?
If the multi-year ice shifted over a period of several months ahead of the expedition launch, why was the Catlin team seemingly surprised upon their arrival to find first-year ice? NSIDC knew it was first year ice in February. This reminds me of Lewis Pugh’s attempt to kayak to the North Pole, at a time when NSIDC maps showed the route blocked by 600 miles of ice.
It sounds like the new European satellite Cryostat-2 will provide the desired ice thickness data, without any geographical bias or concern about snow thickness. Speaking as a former amateur explorer, I certainly appreciate and admire the adventurous nature and grit of the Catlin team. However, I don’t see that there is a lot of scientific value to their ice measurement efforts – particularly given their stated disposition towards arriving at a seemingly pre-determined result.
O/T – it seems my skpeticism regarding the Hadley Center numbers was unfounded. They clearly show that the Global Temperature Anomoly dropped a whole 0.01K from February to March 2009. And I was SURE that the rash of record low temps and record high snow over significant portions of the Northern Hemisphere in March were going to be “corrected” out of the data.
Pardon my skepticism! [/sarc]
OT but this REALLY needs big attention.
http://www.nytimes.com/2009/04/16/science/earth/16degrees.html?_r=1
Look at the photo itself. Indian woman cooking at her stove. The same traditional technique humanity (including neanderthals) used for cooking and creating warmth for thousands of years.
Now look at the photo caption
“Soot from tens of thousands of villages in developing countries is responsible for 18 percent of the planet’s warming, studies say.”
That is an incredible statistic. 18 percent! How did they get that figure when nobody knows how much of the warming trend is attributable to mankind? And why pick on the poor again when they could make historic examples of cities like Paris, New York and London?
Two points:
1. Hundreds of thousands of villages and towns all across the world for thousands of years created soot the same way. Did they cause global warming? How do you work out the percentage? Why have there been cooling periods while villages expanded, multiplied and more soot was generated?
2. Soot and smog block incoming sunlight while trapping some heat that is created by humans. Towns and cities whose soot and smog has cleared up saw warming as more sunlight penetrated to ground level. This has caused temperature monitors to show what looks like manmade warming at first glance but it actually a cleaning of the atmosphere.
Aron 11:41:52
It’s jockeying in the guiltstakes leading up to Copenhagen. The developing countries are going to lay guilt on the developed ones for past carbon use and the developed countries are going to lay guilt on the developing ones for soot. At least, that’s my call from the sidelines.
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Aron (11:41:52) :
OT but this REALLY needs big attention.
That is why we must insist in our WUWT barbecues’ plan.
Oh yeah, and they’ll both lay guilt on each other for present hydrocarbon use. Read Peter Huber in the City Journal, ‘Bound to Burn’. We are not weaning off of hydrocarbon use for energy soon, and it’s a doggone good thing that CO2 has minimal effect on climate, because if it did, we would be in the sort of trouble Hansen fantasizes.
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Dr Meier!
Why doesn’t the US Navy help you?
If they don’t, you can always lease a Swedish submarine like they did, no need to go nuclear.
John F. Hultquist (08:48:10) :
“TWO: For all who have an image of old thick ice on the Arctic Ocean, maybe you missed this:
http://wattsupwiththat.com/2009/04/13/watching-the-2007-historic-low-sea-ice-flow-out-of-the-arctic-sea/#more-7019
Scroll to the video and watch it, noting the date in the upper right. This makes me want to do a ‘search and replace’ on the word ‘melt’ regarding Arctic ice – ‘melt’ to be replaced with ‘flushed out.’”
Excellent point John. If we take ice from the freezer and put it in the fridge, then we shouldn’t be assuming that our freezer is faulty, when the ice consequently melts !
Here’s hoping the good Doctor Meier will make a comment or two to answer some of the questions.
Thanks,
Mike
It is somewhat surprising to see Dr. Meier suggesting that the Catlin data might be helpful:
“Like many scientific expeditions, it seems like they won’t get as much data as hoped, but ground data from the ice is so rare that every little bit helps.”
One would presume that Dr. Meier, recognizing the publicly announced bias of the Catlin expedition (to document thinning ice), would decline to describe the event as “scientific” at all. This bias, noted by Steve Goddard as geophysical selection – so weights the measurements from Catlin as to reasonably dismiss it out of hand.
Add to this, the already embarrassing disclosure of data manipulation, delay in acknowledging equipment failure and lack of time, date, location stamps on visual records – pretty well relegates this adventure to those found at… Disneyland.
Given the straightforward method to measuring ice outlined by Dr. Meier, you must wonder how these measurements can reconcile real volume of ice. Here is underwater photography from the NOAA Arctic 2005 Exploration expedition. The variability of the subsurface ice indicates that true thickness of any ice formation may be far more difficult to determine than by simple tape measure with collapsible metal flange.
http://tinyurl.com/cog4ra
Note images #3 and #4 in the series to get a sense of what lies under the surface.
In case the tinyurl expires – here’s the original: http://oceanexplorer.noaa.gov/explorations/05arctic/logs/july24/media/slideshow/slideshow.html#
Aron (11:41:52) : “OT but this REALLY needs big attention.”
Aron: There is a backstory to this of which you may not be aware. Following the 1st IPCC Working Group report the question was raised as to where they got the notion that fossil fuel burning in developed countries caused the measured increase in residual carbon in the atmosphere. Where was the data? Well, there was no data, but assumptions. So a study was launched. Results were reported in a 2000 issue of Nature that over 50% of the residual carbon in the atmosphere came directly from Third World Home Fires with a noticeable component from the Indonesian peat fires. Well, that didn’t fit what the IPCC wanted, so a second study was launched with results appearing in a 2005 issue of Nature. Those results also showed Third World Home Fires as the culprit with a distinct component in rural China.
An additional note: From the article you cite, “In Kohlua, in central India, with no cars and little electricity, emissions of carbon dioxide, the main heat-trapping gas linked to global warming, are near zero.” That is a bizarre statement. CO2 is released in the creation of soot, so the emissions are no where near zero. It points to the ignorance of many in the media that assume CO2 emissions only come from fossil fuels. Unfortunately, that ignorance is pervasive these days.
Thought this was interesting…
From Wiki:
“The ice in central parts of the Arctic Ocean is on average 2.5 metres (8.2 ft) thick. Nuclear-powered icebreakers can force through this ice at speeds up to 10 knots (19 km/h, 12mph). In ice-free waters the maximum speed of the nuclear-powered icebreakers is as much as 21 knots (35 km/h, 24mph).”
I wonder if this eight foot thick ice is two or three year ice. It seems to me that if anyone needs to know the thickness of the Arctic sea ice, a few well placed calls to the numerous icebreakers, sailing under many flags, would quickly and easily answer the question.
I wonder if the route planned for the Catlin group was influenced by the travel plans of icebreakers also. An icebreaker steaming toward your camp at two AM would certainly be adventurous.
Still wondering if the hugely increased operations of icebreakers in the Arctic could be contributing to the “flushing out ” of the ice.
Pieter F (11:14:32) :
Yes, Billy, I am beinfg [sic] serious. Think about it: their stated goal is to measure ice THICKNESS, not the amount of ice “from the water top.” 85% of the ice volume is BELOW the water’s surface. They need a Kovacs-style ice thickness gauge with the flange device on the bottom so it can catch the bottom of the ice, then pull the tape taut and read the measurement. They don’t seem to have a Kovacs ice thickness gauge. They have a stick.
Oh dear this is getting tedious.
they measure a number of dimensions at each hole
1 snow thickness
2 top water to top ice
3 ice thickness
I assume that the tape is used for 3 and the stick is used for 1 & 2. Geddit?
“Like many scientific expeditions, it seems like they won’t get as much data as hoped, but ground data from the ice is so rare that every little bit helps.”
I would think that any captain of any icebreaker cruising the Arvtic ocean would not only be able to tell you the thickness of the sea ice, but the precise location of those thickness measurements.
See this study:
http://www.geosensors.com/global/prins15.pdf
I’d like to nominate Pieter F’s remark, “off-the-cuff statements that come off like a cocktail of agenda, ignorance, illogical thoughts” as quote of the week.
Cassandra King
What you say may be entirely true. I was not expecting real climate breakthroughs… maybe the cure for the common cold… a new way to freeze skin cancer… a better snow shoe… like our vacationing friend and antibiotics, something entirely unexpected.
They might even read this fine article by Dr. Meier and have a head slapping moment: “Geese is that what we were supposed to be doing?!”
Lower 48 Maximum Snow depth
04-20-04…424.7 in.
04-20-05…494.5 in.
04-20-06…336.7 in.
04-20-07…491.8 in.
04-20-08…665.0 in.
04-20-09…839.5 in.
http://www.nohrsc.noaa.gov/nsa/index.html?region=National&year=2009&month=4&day=20&units=e
Other end of the world but the following story reported in the Fiji Times 20/4/09 might be of interest. To quote the Russian Captain “I just see more and more ice not less ice”!
http://www.fijitimes.com/story.aspx?id=119626
Dr Meier seems to have strange reluctance to call [snip] when he sees it. Does anyone REALLY believe this mob will get any data worth anything at all? That is if they are even on the ice they say they are on? What a pathetic PR stunt by pretentious idiots.
It doesn’t really seem to matter what kind of measuring stick they use. I’m most curious how they establish the top and bottom surfaces of the ice. If they properly measure both the thickness of the ice and the distance from the water surface to the top of the ice, then is should be possible to calculate the density of the ice.
While I think the expedition has at least as much to do with publicity as it does with science, it is possible that they may actually provide some usable information. They would be well advised to provide information regarding methods.
It’s wonderful to have Dr. Walt to help clarify things. Thanks.
I did a little looking on the Kovacsice Drilling Equipment site and found this page http://www.kovacsicedrillingequipment.com/publications/ and the “Handbook for Community-Based Sea Ice Monitoring” PDF. It has the logo of the National Snow and Ice Data Center on it. It appears to show a striking difference in how sea ice is to measure and the reports from Catlin.
I for one am simply worried that high profile expeditions like Catlin appear to use shoddy methods and are quite willing to present false data (the live from the ice nonsense). Why should I accept anything these people do. Even if the data shows vastly more ice than we expect I can’t accept it.
Marc @ur momisugly 16:28:35 “Why should I accept anything these people do.”
In a court of law, if a witness is shown to be lying about even one small thing, their entire testimony can be disregarded and considered unreliable.
Bill, you seem rather young, based on your posts. Which means you are idealistic and trusting of whatever entity agrees with you. It comes with the territory of being young it seems (didn’t used to be that way). Try this on for size: Question everything, even your own beliefs. Youth used to be really good at this. Not so much anymore.
Very nice to read the good Dr Meier’s description of their procedures. I suspect he only scratched the surface, of what people can use that data for; and I’m not going to prejudge the value of knowing.
My ex Navy contact says they know a whole bunch about that ice, that they are not about to tell anybody; which is fine with me. But he did say that on average all over the whole area about one metre thickness is about typical; that’s also about the thickest that the Navy likes to surface through unless they have to.
But given how it gets moved around by wind and tide, and seas, I’m sure it cracks and buckles, and piles up into some quite thick local areas; but not like Antarctic sheets.
And when it melts each summer, the water below sucks a whole 18-20 ppm of CO2 out of the atmosphere above the arctic ocean; how cool is that.
So much for the 200 year CO2 residence time BS that the MMGWCCers try to feed us. In any case; an IR photon needs about one millisecond to escape to 300 km from the surface; so it only needs to encounter one H2O or CO2 molecule on that journey to get captured; so the GHG only needs to be there for the same one msec. So nuts to those who say they don’t count water vapor, because it is removed from the atmosphere quickly. It’s actually very slow compared to the needed one msec encounter time.
George
@Marc (16:28:35) :
You wrote: “It’s wonderful to have Dr. Walt to help clarify things. Thanks.
I did a little looking on the Kovacsice Drilling Equipment site and found this page http://www.kovacsicedrillingequipment.com/publications/ and the “Handbook for Community-Based Sea Ice Monitoring” PDF. It has the logo of the National Snow and Ice Data Center on it. It appears to show a striking difference in how sea ice is to measure and the reports from Catlin. […]”
Thanks for that link. It answered one of my questions. It looks to me that if the ice is reasonably flat top and bottom, the measurement precision appears to be about +/- 1cm and maybe a tad better than that.
Now if you carefully record the location of the hole on the arctic ice using GPS well, in three to four days you’ll have no clue where that hole went due to ice drift. Ah well.