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.
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Dr. Walt Meier…
Thanks a lot for your detailed explanation on ice survey techniques.
Personally, I have not questioned the importance of the Catlin group for a better understanding of the physical state of the arctic frozen layer; nevertheless, the intention of the mission clearly is biased to AGW cause, never in support of scientific knowledge. Perhaps their techniques are correct, perhaps they are not; I don’t know. What I know for sure is that the results will not prove, absolutely, that human beings or carbon dioxide emitted from human activities are the drivers of the arctic ice melting.
To be clear, published scientists and researchers have had their hands slapped for sloppy work, and in a very public way. I see no reason why this same effort to keep scientific work above board cannot be applied in this instance.
Having worked in the Canadian North in the winter doing mineral exploration I can attest to the problems with gathering useful data at temperatures less than 20 below. Everything take seemingly twice as long and equipment breakdowns are more frequent. Productivity was woefull however one cannot walk on a frozen lake during the summer.
This was 20 or more years ago and there has been significant improvement in equipment since then. We used to go through cases of high priced alkaline batteries in our geophysical instruments as they only lasted hours at minus 20 as opposed to days in the summer. (Now one just steam heats the battery to get it to work).
I’ve drilled many holes through the ice with a hand auger, mostly less than a meter. It’s hard work and anything over 30 cm takes considerable time. One drill hole mesasurement using a hand auger will likely take one to two hours
Today’s post from the ice (with it’s improbable photo) notes that they are completing 7 to 9 hours of non-stop topographical observation and 3-5 hours of static observations and recording up to 76 such observations (25 per person) per day.
This sounds significant if they are recording data at 76 specific locations.
Or are they just recording an avarage of 76 bits of data per day.
Given the expeditions history of selective disclosure I suspect we have been given another dose on non-information.
I also don’t think I’ll be using the data generated by the Calin crew.
Steven Goddard wrote:
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?
But given that Dr. Walt Meier wrote:
… (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.
So more to the point I think is the question “What is the source of the Catlin Team’s expectations regarding snow cover?”
Related:
“Fargo flooding was not due to global warming, It was a natural event aggravated by a colder winter and more snow
Obama flunks Global Warming 101 on Fargo
By Dr. Tim Ball
“When the freedom they wished for most was the freedom from responsibility, then Athens ceased to be free and never was free again.” Edith Hamilton.
President Obama used recent flooding in Fargo, North Dakota to push his misguided belief in global warming. His comment, “If you look at the flooding that’s going on right now in North Dakota and you say to yourself, ‘If you see an increase of two degrees, what does that do, in terms of the situation there?’” is speculative and completely wrong.
A two-degree warmer North Dakota would mean less snowfall, therefore less flooding. Spring flooding along the Red River of the north is due to snow melt and the geography of the region. This year the cold winter caused heavy snow in the south basin and all across the northern continental US. Obama’s comments do what the focus on global warming does; diverts us from real issues. In this case it is flooding and people living in naturally high-risk areas.
I was a founding member of the International Coalition, a joint project of citizens from Canada and the US living in the flood plain of the Red River.
Failure of the federal governments on both sides of the border to deal with flooding forced creation of this illegal organization. I won’t forget riding on the bus to the first meeting at the University of North Dakota and listening to the US federal government bureaucrat in the seat in front of me saying to his assistant, “Which way does this bloody river run anyway?” Later I was the first Chair of the Assiniboine River Management Advisory Board (ARMAB) set up to establish management plans for this river, which is the largest tributary of the Red.
The Red River is the largest and one of very few rivers that start in the US and flow north into Canada. This is not an accident but a result of history. The 49th parallel in western North America was a simple geometric boundary that effectively approximated the divide separating water flowing south into the Gulf of Mexico or north into Hudson Bay. The Hudson’s Bay Company was granted land draining into Hudson Bay and that land became part of Canada in 1870 under the British North America Act.
Rivers usually create their own valleys but the Red River runs through lowland formed and occupied by Glacial Lake Agassiz. This lake was created by the meltwater from the Wisconsin ice sheet. Figure 1 shows a reconstruction of the ice at an early stage of lake development, but the middle stage of ice sheet melting.”
http://canadafreepress.com/index.php/article/10390
Many thanks Dr Meier.
The US,Royal,French and Russian navies have nuclear submarines under the ice for most of the year and they are taking upward looking sonar measurements most of the time. There must be a vast library of information here. Is much of it released into the public domain?
BTW, the North Pole Environmental Observatory station recently installed for this yearis available here and that is this station.
“Oh, and this is not an amateur project. They’re getting paid, or at least fed, for this work, so they’re professionals. I don’t know if that disqualifies them from the Winter Olympics.”
But their methods are amateurish!
This sounds a lot like what I used to hear from my apprentices during my “teaching” years.
Me: So, how did the repair go?
Apprentice: Well, it runs like crap, and I don’t understand why, but it’s running. So that’s good enough… Isn’t it?
Me: No. It’s not “good” because you haven’t done it “enough”! Start again, and pay attention this time!
Dr. Meier states; “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.” Say what? Dr. Meier goes on to more or less say that the cost is too great to do a truly effective survey, so we must accept piecemeal and inferior data as that is all we can get. Yikes! Considering the cost of not doing this, and instead relying on ineffective and unproven data, I would argue that spending 500 million, or several billion dollars on this work is cheap by comparison. I am also dismayed with Dr. Meier’s use of weak economic factors to restrict his own admittedly limited research! Why not put millions of observers out on the ice and get it over with? It is clear that empirical observation is desperately needed here. I think folks are freaked out enough about this issue to acquiesce to spending the large sums needed for such important work.
I join with others in thanking Dr. Meier for having the courage to address us in this forum. It takes obvious intellectual strength and guts to wander into the “lions den” the way he has. I cannot, however,agree with his conclusions on the subjects he raises here. Much more needs to be done before this is even “good enough”; let alone good.
Thank you.
Unknown Waters is a book about a submarine survey of the Arctic. It made clear that ice draft could change very quickly. The sub was once stuck in an “ice garage” and had to back out very slowly.
Pamela Gray (09:11:06) :
To be clear, published scientists and researchers have had their hands slapped for sloppy work, and in a very public way. I see no reason why this same effort to keep scientific work above board cannot be applied in this instance.
If I’ve understood your question, my answer would be as follows: because the objective of this ice survey is not scientific, but for sake of growing the quotes of insurances and AGW myth. I cannot trust a biased work for the sake of political or economical objectives. How could I know that the Catlin’s group is not picking only the convenient data and discharging the inconvenient ones? How could I trust a work which is flawed since its beginning towards AGW crusade?
Reason. Science. Just the facts.
Thank you, Dr.Meier. For so many reasons.
Snow acts as an insulator. If you ever been on a frozen lake in winter, you can remember that the area with more snow on the ice will have ice that is less thick and even you find water under the snow.
So, the same applies for Artic ice. It should be normal that if there is more snow up there, due to increased precipitation because of global cooling, you could expect to have thinner snow over time. But I guess, when it melts in summer, it should freeze even more the next year round.
Maybe the Catlin mission will generate useful data on snow vs. ice composition but I wish they hadn’t used preconceived conclusions in their description of the mission.
I wonder how they will word their final results. “With Arctic sea ice increasing at 500,000 square kilometers per year, it will all be gone in X years.”
Dare they put in a negative number for X?
P Folkens (07:25:23) :
Dude! As Dr. Meier points out “. . . most of the ice (~85-90%) is below the surface [of the water] . . .” If, as you think you read somewhere, their measurement if from the ice top to the water in the hole, they will be missing 85% of the ice because “water seeks its own level.”
Are you beinfg serious!!!!!!!!!!!!!!!!! They take a measurement from water top to ice top. They take a measurement from Ice top to snow top with something stiff – a ruler!!!!!!!!!!!!. Why they make this measurement I do not know. The tape measure (a floppy thing with an attachment on the end – which I pointed out in the Catlin photo is used to measure the ice thickness.
Pamela Gray (08:30:09) :
If this truly were an effort to substantiate ice conditions with ground sonar and not a publicity stunt, the same re-supply helicopter would have been employed to run out to a spot, drop a team, take
The plane has to refuel once to reach them (not a helicoptor) twice eventually.
A helicopter uses more fuel. Would you like to land on ice which has not been inspected, in a plane?
Thanks Dr. Walt Meier for the authoritative review of the current state of the ice measurement technology.
Perhaps a more important question is — if you were designing an ice measurement expedition, (funding no object) what bits of data would you be looking for?
What sort of measurement resolution, spacing and or gridding would be most useful to field check the satellite data?
Would it be more useful to sit on an ice flow and periodically re-measure the same piece of ice along with recording the air temp history?
Would a linear transect with measurements every x meters be more useful than a carefully gridded 1 KM square?
From you comments it sounds like careful measurement of both the free board and the true ice thickness at the same spot would also allow you to estimate the ice density.
I was thinking that to cover a lot of ground (ice) in reasonably sheltered environment an air cushion vehicle might be useful, (although difficult to control in high winds) unless it was built with the ability to operate in that sort of environment. The over surface speed of a hover craft and its ability to cross water would allow a very large area to be covered quickly without the risks of flight in icing conditions.
For systematic ice thickness surveys you could combine military cold weather training with a long term ice measurement mission. The team members need to do cold weather movement exercises anyway, why not give them a practice mission to go measure a 100 meter grid on the ice?
No country could afford to systematically map the ice thickness of the whole arctic but a cooperative effort of the major nations which abut the arctic or have direct interest in it could get perhaps 10 – 20 high quality measurement missions each winter season, and pool the data. Over a 20 year span that would build a useful reference data set.
Larry
vanderleun (01:44:45) :
> Re: drilling. How do you know the hole you drill is plumb? Can you game the system if you drill at a slant?
Of course you can, but the tilt has to be pretty steep to get a severely wrong measurement. Here’s a table of angles (degrees from vertical) and error factor for that angle.
>>> r = 180/3.14159
>>> for t in range(0.0, 90.0, 5.0):
… print ‘%2d %5.2f’ % (t, 1.0 / cos(t / r))
…
0 1.00
5 1.00
10 1.02
15 1.04
20 1.06
25 1.10
30 1.15
35 1.22
40 1.31
45 1.41
50 1.56
55 1.74
60 2.00
65 2.37
70 2.92
75 3.86
80 5.76
85 11.47
The auger would have to be tilted 25 degrees to come up with a measurement 10% too high.
In practice, depending on the drill handle shape, just finding the balance point of the auger bit will be plenty close to vertical.
The AMSR-E ice extent in the sidebar is now showing a distinct seven year high.
I’m glad to see others commenting on the submarine measurements. Are there any submariners that could comment on the problems with releasing ice thickness measurements from the Navy? I’m guessing that there might be problems with running active sonar while trying to be stealthy, although bumping the roof would seem to be a greater risk. Also one would not want confirm a date and location where a submarine was that could be used to validate submarine detection efforts by the opposition. Still it seems that the satellite calibration could be done by those with the proper security clearances without releasing any classified data.
I’m just not getting this.
I haven’t read everything on this ice measuring treck to the pole, but I can’t imagine how this crude collection of ice measurment will have any value or usefulness at all.
I mean all it will tell anyone is what the ice thickness appeared to be at that time at those locations they measured. So that means what?
Are we to look forward to some interpolated importance at a later date?
What is it?
Pamela Gray and INGSOC are absolutely right. If polar ice thickness data is as important as Dr. Meier and the Catlin website say it is, why aren’t they making a serious effort to obtain the ice data. This is NOT serious science! I’m not a scientist but, in my work I collect data, document conditions and analyze the data. The difference is, when that work is finished there’s a “hot seat” and a dozen attorneys who are highly motivated to impeach the work in a deposition. If the “road to hell” is paved with good intentions, the base supporting the paving is bad methods and poor documentation (believe me!) I’m sure that in most areas of science they have a strict peer review, I’m just afraid that in the case of AGW “scientists” look the other way.
bill (10:18:01) : “Are you beinfg serious!!!!!!!!!!!!!!!!! They take a measurement from water top to ice top.”
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.
Unfortunately, you represent the core of the AGW cadre. You really need to think things through before making off-the-cuff statements that make you come off like a cocktail of agenda, ignorance, illogical thoughts.
I think next time these guys won´t need to go that far, they will be measuring Thames river ice depth. 🙂
Every time I think about the US Navy and what it knows about arctic ice, I can’t help think that they know a whole lot more than they will ever tell us.
The same holds true for the ocean sub-surface currents and typography.
bill,
I did not notice that you are rounding me up for stating my opinion on the Catlin Arctic fraud.
Bring. It. On.
John H-55 at 11:01:01
Presumably their data will be compared with data from other modalities measuring ice thickness at the same time and same place, but that presumes that they are documenting their exact position, and measuring with precision and accuracy. Not much evidence of that, yet. If they are doing so, there will be scientific value to their work. If they are not doing so there will still be propaganda value to their work, depending upon the gullibility of their public. I think the jury is still out.
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