NIC charts are produced through the analyses of available in situ, remote sensing, and model data sources. They are generated primarily for mission planning and safety of navigation. NIC charts generally show more ice than do passive microwave derived sea ice concentrations, particularly in the summer when passive microwave algorithms tend to underestimate ice concentration. The record of sea ice concentration from the NIC series is believed to be more accurate than that from passive microwave sensors, especially from the mid-1990s on (see references at the end of this documentation), but it lacks the consistency of some passive microwave time series.
National Ice Center Arctic Sea Ice Charts and Climatologies in Gridded Format
The only rational way to interpret this paragraph is that passive microwave measurements are consistently less accurate. Read this again
The record of sea ice concentration from the NIC series is believed to be more accurate than that from passive microwave sensors
You can’t be more accurate and less consistent. It makes no sense mathematically. If your error bars are smaller, then you are -by definition – more consistent.
“The record of sea ice concentration from the NIC series is believed to be more accurate than that from passive microwave sensors”. OK, that statement makes sense; it seems difficult to misinterpret the meaning.
But, “it lacks the consistency of some passive microwave time series” seems ambiguous to me. Consistency? What kind of consistency? Consistency of day to day comparisons? Consistency of measurements, or perhaps consistency of rates of change? Can they perhaps clarify in what particular way NIC series are less consistent than microwave series?
Its pretty simple. The passive Microwave will miss some ice, but it will miss that ice consistently.
That is, it will consistently over time miss ice that is smaller than its pixel. It will also consistently miss some ice at the margins and I believe has some issues with landed ice since it relies on a land/ocean mask. So, it will consistently be 10-20% low, lets say for example ( read the papers I cant recall the exact figure )
The operational charts can be more accurate in a given year. They rely on human operators ( which change ) and on models. So they might miss 0 ice one year, and 5% the next, and over estimate yet another year. Very simple.
Truth: 5,5,5,5,5,5,5,5,5,5
Consistent: 4,4,4,4,4,4,4,4,4.
More Accurate, less consistent: 5,4,5,4,5,4,6,4,5.
The passive system is more consistent because its shortcomings ( pixel size) doesnt change year in and year out.
The system with humans and models in the input stream is more accurate BUT less consistent.
When you want to keep records on a long term basis consistency matters. Since the difference
is known and small for the consistent system, you can use it for long time scale records.
Missing a few hundred K of ice consistently is not a problem. What would be a problem is if
your error changed year to year. In that case you new record could be because you had a new human counting the ice.. or the model could be tweaked year to year.
It does with the different dection methods used. ya know it’s not the same af what your grandfather used kind of Appells and Water Mellons and Oranges.
You are assuming that the distribution of ice sizes and shapes is consistent from year to year, which it isn’t. As Julienne explained, the August storm fragmented huge areas of ice.
Regardless, you will always get more consistent comparisons from more accurate data. Being consistently wrong offers no value scientifically.
Well that is super models fer ya! 😆
Right, very well. Point made & all.
But the problem with this is that in reality you have something that far more resembles:
Truth: ?,?,?,?,?,?,?,?,?,?
Purportedly consistent: 4,4,5,4,4,5,4,4,4,4
Purportedly more accurate: 4,6,5,4,6,5,5,4,4,5
Means they don’t know!
http://joannenova.com.au/2012/09/wind-farms-are-96-useless-and-cost-150-times-more-than-necessary-for-what-they-do/
I am surprised Steven, as anyone who ever fired a few shots with a rifle should understand the difference. (and Mosher gave a perfect explanation)
At the end, the guy with the more consistent dispersion pattern mostly is the better shot and all those holes close together in the 9-ring are caused by a problem with the rifle…
Whatever Son Of Daft!
A stopped clock gives the same answer every time, like your brain does.
😆
LOL! Nice one!
On another blog, a climate person put it to me this way:
“Based on what I’ve read if I had no other source, or were heading out in a boat, I would most certainly use the operational indices such as NIC. For climate change trends, I’d go with NSIDC, JAXA … Do you know of any climate scientists that prefer NIC?”
Actually, I do know of some such scientists:
“Passive microwave sensors from the U.S. Defense Meteorological Satellite Program have long provided a key source of information on Arctic-wide sea ice conditions, but suffer from some known deficiencies, notably a tendency to underestimate ice concentrations in summer. With the recent release of digital and quality controlled ice charts extending back to 1972 from the U.S. National Ice Center (NIC), there is now an alternative record of late twentieth century Northern Hemisphere sea ice conditions to compare with the valuable, but imperfect, passive microwave sea ice record.”
From Late twentieth century Northern Hemisphere sea-ice record from U.S. National Ice Center ice charts, Partington, Flynn, Lamb, Bertoia, and Dedrick
http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1058&context=usdeptcommercepub
Bottom line: If you are looking for decadal anomalies in ice coverage, microwave products are more trustworthy. If you want to know what is happening with ice in this year’s melt season, NIC ice charts are more accurate.
If they state that something is “accurate” or even “more accurate”, it implies they know what the true value is. If, in fact, they somehow know what the true value is, why not use the method they used to obtain the true value? As it is, they assign an arbitrary “true” value to determine that the method they used to obtain their “more accurate” value is “more accurate”. The fact is, they are simply using the results they prefer and are calling it “more accurate”. Their version of science seems to use the idea that a thing IS its name. By changing the name they change the thing. There is a word for this: technobable. It’s technobable all the way down.
All we really know is that there is a huge amount of ice at the poles and that the location of the edges of that ice changes over time roughly in step with the seasons. Estimates vary. Unfortunately, in a way more dependent upon what is attempting to being proved than on what is actually KNOWN. More to the point, we don’t know how much a change in the position of the edge of the ice changes the total amount of ice.
Lionell, I agree with what you say. No one knows for certain how much ice there is. We have different authorities with differing methods and estimates.
But a point must be made about empirical vs. computed results.
Russia operates 75 ice-breakers in the Arctic. When they encounter ice in places where microwave products say there is no ice, then it is confirmed that those indices are underestimating the ice extent, certainly in the areas so sampled, and probably across the entire polar region
According to the MAISIE documentation
Furthermore, the use of visible and SAR imagery during summer melt seasons means that IMS product accuracy does not degrade as much as does the accuracy of products based solely on passive microwave data, when surface melt water attenuates the passive microwave signal. This microwave attenuation leads to underestimates of the ice concentrations, particularly along the marginal ice zone during the summer.
http://nsidc.org/data/docs/noaa/g02186_masie/index.html
Paul,
The latest daily NSIDC figure is 3.689 million square kilometers. That’s more than 450,000 square kilometers below the 2007 minimum. It is unlikely that such a large difference can be explained solely by the passive microwave missing ice concentrations in the marginal ice zone. It should be noted that the same technology was used to measure 2007, therefore one is essentially using the same measuring stick. Finally, the fact that other data (ice extent from JAXA, area from Cryosphere Today, and volume from PIOMAS) are well below 2007’s figures adds confidence that the record is real, not the result of missed ice.
Blah blah blah blah … NATICE is 12% above the 2007 minimum
But nevertheless we still have large discrepancies between the two methods that don’t seem to have existed previously.
What I am arguing for is being brutally, openly, and explicitly truthful about our state of knowledge of things. The word “accuracy” has no genuine place in scientific communication because it is a comparison with the true value. If we know the true value by some method, then let us discard all other methods and simply use that method. However, can we escape the issue that to know a particular method gives the true value without having a prior method that gives the true value? No we cannot. Hence, state the method, show your work and measurements, and then state only what we really do know: we measured such and such by this method and this is our result. The word “precision” has a place in the measurement of extent or intensity in science but the word “accuracy” does not simply because it cannot be determined.
In the matter of the difference of results with the use of different methods. We can say they are different and we can say one gives a lower or higher result than the others. Then, we can apply still different methods and find still more differences between methods. While we might be able to argue that one particular method is better than the others based upon it being a more direct measurement, it too has the problem discussed above.