The DMSP satellite is still operating, but the SSM/I sensor is not
Regular readers will recall that on Feb 16th I blogged about this graph of arctic sea ice posted on the National Snow and Ice Data Center sea ice news page. The downward jump in the blue line was abrupt and puzzling.
Click for larger image
Today NSIDC announced they had discovered the reason why. The sensor on the Defense Meteorological Satellite Program (DMSP) satellite they use had degraded and now apparently failed to the point of being unusable. Compounding the bad news they discovered it had been in slow decline for almost two months, which caused a bias in the arctic sea ice data that underestimated the total sea ice by 500,000 square kilometers. This will likely affect the January NSIDC sea ice totals.
Figure 1. High-resolution image Daily Arctic sea ice extent map for February 15, 2009, showed areas of open water which should have appeared as sea ice. Sea Ice Index data. About the data. Please note that our daily sea ice images, derived from microwave measurements, may show spurious pixels in areas where sea ice may not be present. These artifacts are generally caused by coastline effects, or less commonly by severe weather. Scientists use masks to minimize the number of “noise” pixels, based on long-term extent patterns. Noise is largely eliminated in the process of generating monthly averages, our standard measurement for analyzing interannual trends. Data derived from Sea Ice Index data set.
Figure 2.
High-resolution imageDaily total Arctic sea ice extent between 1 December 2008 and 12 February 2009 for Special Sensor Microwave/Imager SSM/I compared to the similar NASA Earth Observing System Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor. —Credit: National Snow and Ice Data Center
Dr. Walt Meier of NSIDC had planned to do a guest post here on WUWT, but this evening, with the magnitude of the problem looming, he’s asked to defer that post until later. I certainly can’t fault him for that. He’s got his hands full. Hopefully they have a contingency plan in place for loss of the sensor/space platform. I applaud NSIDC for recognizing the problem and posting a complete and detailed summary today. I’ve resposted it below in its entirety. Note that this won’t affect other ice monitoring programs that use the Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor, which is on an entirely different platform, the AQUA satellite.
UPDATE: 2/19 Walt Meier writes with a clarification: “One detail, though perhaps an important [one]. I realize that it is bit confusing, but it is just one channel of the sensor that has issues. And it isn’t so much that it “failed”, but that quality degraded to the point the sea ice algorithm – the process to convert the raw data into sea ice concentration/extent – failed on Monday.” – Anthony
From NSIDC Sea Ice News:
As some of our readers have already noticed, there was a significant problem with the daily sea ice data images on February 16. The problem arose from a malfunction of the satellite sensor we use for our daily sea ice products. Upon further investigation, we discovered that starting around early January, an error known as sensor drift caused a slowly growing underestimation of Arctic sea ice extent. The underestimation reached approximately 500,000 square kilometers (193,000 square miles) by mid-February. Sensor drift, although infrequent, does occasionally occur and it is one of the things that we account for during quality control measures prior to archiving the data. See below for more details.
We have removed the most recent data and are investigating alternative data sources that will provide correct results. It is not clear when we will have data back online, but we are working to resolve the issue as quickly as possible.
Where does NSIDC get its data?
NSIDC gets sea ice information by applying algorithms to data from a series of Special Sensor Microwave/Imager (SSM/I) sensors on Defense Meteorological Satellite Program (DMSP) satellites. These satellites are operated by the U.S. Department of Defense. Their primary mission is support of U.S. military operations; the data weren’t originally intended for general science use.
The daily updates in Arctic Sea Ice News & Analysis rely on rapid acquisition and processing of the SSM/I data. Because the acquisition and processing are done in near-real time, we publish the daily data essentially as is. The data are then archived and later subjected to very strict quality control. We perform quality control measures in coordination with scientists at the NASA Goddard Space Flight Center, which can take up to a year. High-quality archives from SSM/I, combined with data from the earlier Scanning Multi-channel Microwave Radiometer (SMMR) data stream (1979–1987) provide a consistent record of sea ice conditions now spanning 30 years.
Data error sources
As discussed above, near-real-time products do not undergo the same level of quality control as the final archived products, which are used in scientific research published in peer-reviewed journals. However, the SSM/I sensors have proven themselves to be generally quite stable. Thus, it is reasonable to use the near-real-time products for displaying evolving ice conditions, with the caveat that errors may nevertheless occur. Sometimes errors are dramatic and obvious. Other errors, such as the recent sensor drift, may be subtler and not immediately apparent. We caution users of the near-real-time products that any conclusions from such data must be preliminary. We believe that the potential problems are outweighed by the scientific value of providing timely assessments of current Arctic sea ice conditions, as long as they are presented with appropriate caveats, which we try to do.
For several years, we used the SSM/I sensor on the DMSP F13 satellite. Last year, F13 started showing large amounts of missing data. The sensor was almost 13 years old, and no longer provided complete daily data to allow us to track total daily sea ice extent. As a result, we switched to the DMSP F15 sensor for our near-real-time analysis. For more information on the switch, see “Note on satellite update and intercalibration,” in our June 3, 2008 post.
On February 16, 2009, as emails came in from puzzled readers, it became clear that there was a significant problem—sea-ice-covered regions were showing up as open ocean. The problem stemmed from a failure of the sea ice algorithm caused by degradation of one of the DMSP F15 sensor channels. Upon further investigation, we found that data quality had begun to degrade over the month preceding the catastrophic failure. As a result, our processes underestimated total sea ice extent for the affected period. Based on comparisons with sea ice extent derived from the NASA Earth Observing System Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor, this underestimation grew from a negligible amount in early January to about 500,000 square kilometers (193,000 square miles) by mid-February (Figure 2). While dramatic, the underestimated values were not outside of expected variability until Monday, February 16. Although we believe that data prior to early January are reliable, we will conduct a full quality check in the coming days.
Sensor drift is a perfect but unfortunate example of the problems encountered in near-real-time analysis. We stress, however, that this error in no way changes the scientific conclusions about the long-term decline of Arctic sea ice, which is based on the the consistent, quality-controlled data archive discussed above.
We are actively investigating how to address the problem. Since we are not receiving good DMSP SSM/I data at the present time, we have temporarily discontinued daily updates. We will restart the data stream as soon as possible.
Some people might ask why we don’t simply switch to the EOS AMSR-E sensor. AMSR-E is a newer and more accurate passive microwave sensor. However, we do not use AMSR-E data in our analysis because it is not consistent with our historical data. Thus, while AMSR-E gives us greater accuracy and more confidence on current sea ice conditions, it actually provides less accuracy on the long-term changes over the past thirty years. There is a balance between being as accurate as possible at any given moment and being as consistent as possible through long time periods. Our main scientific focus is on the long-term changes in Arctic sea ice. With that in mind, we have chosen to continue using the SSM/I sensor, which provides the longest record of Arctic sea ice extent.
For more information on the NSIDC sea ice data, see the following resources on the NSIDC Web site:
- Sea Ice Index
- Why is the Sea Ice Index product used to study sea ice?
- Do your data undergo quality control?
The extent of corruption of data will turn out to be vastly greater than has thus been revealed. That’s just the way of incidents like this. First limited hangout, then later, full revelation.
It became clear to those simply watching the weather that the trend of world temperatures had turned in late 2007, but officialdom said nothing. Later it would be revealed that they perfectly well knew that a cold turn was in process but continued to realize false warnings of global warming just as inaccurate. I find it humorous that when officialdom scares the populace with AGW these days, the appeal is always to 2007 data.
What is the answer? The same as it has been since the Renaissance. Go to the sources. Quit listening to experts whether they are dressed in Medieval frocks or White lab coats. Examine data for yourself and make your own conclusions. If you made it thru high school physics and math, you probably will come to more accurate conclusions than listening to the politically influenced science establishment.
I find little credence in protests that while the Arctic land mass is very cold the Arctic sea is very warm. Please.
“realize” above should be “release”
The AMSR-E chart from NSIDC shown in the post above has Arctic sea ice extent close to 15 million km2.
Yet the Jaxa website which is also using the AMSR-E data as well is only showing a little over 14.18 million km2. An extra 700,000 to 800,000 km2 would put the sea ice extent well above normal right now.
So there still seems to be some problem.
http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm
“However, we do not use AMSR-E data in our analysis because it is not consistent with our historical data. Thus, while AMSR-E gives us greater accuracy and more confidence on current sea ice conditions, it actually provides less accuracy on the long-term changes over the past thirty years.” I think what he really means here is that the new, AMSR-E data, calls into question the accuracy of their old, SSM/I data. It would be interesting to see a graphical overlay of concurrent data to see what the problem/difference is. Why are they so reticent to embrace a new technology with,”greater accuracy and more confidence on current sea ice conditions”?
One must always remember, just because your a paranoid don’t mean them B*$tards ain’t plotting against you.
They have stated that they want to maintain consistency for the purpose of analyzing the long term trend. This was the reason given for not switching to an available more accurate sensor on a different sattelite. There is a problem with this approach in that eventually all the sensors of this type will fail. So a switch is inevtible. They may as well get on with it in order to have some data instead of a hole. Certainly new sattelites will not include an outmoded sensor array just so their data can look consistent. Somebody help me out with this concept.
From the NSIDC statement: “We stress, however, that this error in no way changes the scientific conclusions about the long-term decline of Arctic sea ice,….”
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By “long-term” I assume the reference is to the full satellite record which goes back about 30 years. Of course, that’s hardly long-term at all when we’re talking about climate. As I understand it, if you really look at the long-term records (e.g. over the last few centuries) then the current melting is nothing at all unusual. A previous large melting peaked around 1922 and there was a lot of media interest (e.g. the opening of the NW Passage), just as there has been in recent years.
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Just as in 1922, we may be close to the peak of the melting and may see significant ice growth over the coming years. Or we may not. That’s why the whole question of climate change is so interesting….
Chris
Why not check out the AMSR-E chart here to compare agains the failed one.
http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm
you will note this too has surges, flat lines, and decreases.
You also will see that the current year is roughly following 2008/2004 curves.
Mike
The satellite data goes back to 1972, or 37 years.
I don’t know why they chose to restate the old records back to 1979 only. Perhaps because the trend from 1974 to 1979 was for increasing sea ice extent and 1979 was the peak.
So — does this mean that the content of Anthony’s first post on the problem really was “news” worth blogging about?
“Lubos Motl (03:39:01) :
would be ruled out according to the conventional statistical criteria”
This only makes sense.
Several Posters have mentioned Cryosphere
I check this site regularly to watch the ice extent. Does Cryosphere use the NISDC data to formulate their graphs?? Or .. are they using a different source??
Not only was the astonishing error worth blogging about, but it appears that Anthony’s (and others) blogs brought a halt to extremely bad data gathering from deteriorating equipment. The kudos go to Anthony; Dr. Meier is the one who should be grateful.
Leon Brozyna (22:49:26) :
Probably a good analogy is the USHCN network. As older manually read max/min thermometers in tired Stephenson Screen boxes are being replaced by new electronic MMTS sensors, those provide a more accurate, less error-prone data source. Being replacements, their data stream is spliced onto the older max-min data stream and overall quality is improved, life is wonderful, and everyone won. Yay!
Except for one thing.
As discovered by surfacestations.org (one of the great creations in citizen science in my book), the MMTS sensors are often located closer to buildings, the plastic shield elements may crud up faster than the Stephenson Screens, and the net result is an erroneous climate warming signal.
We may have been better off to keep the old system or at least put the MMTS sensors inside the Stephenson Screens and use a wireless link to get the data inside. Given issues with my wireless weather station, I’d insist on keeping a copy of the data on the transmitter side!
What should be done with the AMSR-E data, and almost certainly is, is to compare its data with the older sources and investigate discrepancies. This doesn’t need to be done in realtime, but should be done so that data that might help explain issues is still around.
I’m sure things are exciting at the NSIDC this week. 🙂
BTW, I’m strongly in favor of having realtime but questionable data available along with brief and detailed statements about potential sources of error.
Bill Illis you have made a good point.
Why is there such a large discrepency in same (?) AMSR-E data that both NSIDC and JAXA are publicly reporting?
Further, it would appear NSIDC/AMSR-E data for February 2009 is very close to 1979-2000 average for Artic sea ice extent.
Could it be that recent and significant downward trend in Artic sea extent from 2002 is mainly due to instrument error, and that error went undiagnosed because the scientists were expecting a downward trend to fit the AGW hypothesis.
It would seem that instrumental accuracy and has been sacrificed for scientific consistency. That must be a first in physical science.
Many years ago I knew a man that worked building roads for a country in South America. He was paid by the foot. It was a very poor country so no one had a tape measure. My friend, however, did have a length of pipe that he told the inspectors was 20′ feet long. Actually, it was only 19′ long. At the end of each day this faulty measuring device was used to determine how much money the road building company had earned.
I wonder if they are still using that old piece of pipe down there in the interest of consistency.
I bet that the bad data is low. Any takers?
Wow! Inaccurate data because of faulty measuring equipment. Hey Anthony! Maybe you should investigate if that could be a problem in other areas as well. 😉
VG-
Note that Mr. Will stipulated
** Global ** sea ice levels
The Arctic is but one part of the global sea ice total.
According to some sites, the Antarctic sea ice extent is very large this year.
I suspect that the sum of Arctic and Antarctic sea ice levels for Jan 2009, are very equivalent to the combined (global) total for 1979.
It is more than a little problematic that they didn’t know the sensor was not functioning and that news stories were published on bad data. It was easy to see the data was diverging from what was typically expected, yet for over six weeks no one noticed? Was no one looking … The divergence was enough that it should have tweaked their natural curiosity. Couple that with the data blanks that were showing, the warning signs were there that something was going awry.
I sure would hope that the news stories that were released on bad data would be corrected by noting the failure, but, will the news media give the same space and prominence to correcting the error. It seems the news stories are all written about the worst data, data that supports the AGW hoax, and other data us discarded because it may diverge from the desired result. This is what science has now become.
I am not ragging on anyone, but isn’t science all about maintaining that razor edge of curiosity when things don’t turn out as expected, or when they do?
Frankly, I think they may want to fix their internal organization problems at the same time. They generated their own credibility problems.
Newbie here – sorry if my question brings obvious answers by the educated ones.
Isn’t the AMSR-E historical data available somehow and can’t it be used to establish a correlation to the SSM/I data? From that point, apply the correlation factor and start using only the AMSR-E sensor… Or am I missing something?
I also applaud the very open statements about the sensor issue but I question the “(…) we do not use AMSR-E data in our analysis because it is not consistent with our historical data” part. If its data isn’t consistent, find out where it is (after all, if both sensors were measuring the same thing, data should be correlated except for a few questionable portions). Any oddity may then be arguably blamed on sensor issues (be it drift or malfunction).
Sensors and measuring equipment always needs to be replaced eventually, so it’s always a good idea to calibrate multiple measuring instruments together and correlate them to each other. This way you can eventually replace any defective sensor/measuring device with another, start applying the correlation factor and then only use the new sensor to keep your data accurate. I don’t understand why this cannot be done here – or at least why the excuse is to keep using defective sensors instead of more accurate (and hopfully non-faulty) ones.
First, I applaud Dr. Meier for owning up to this and initiating a thorough investigation of the problem. I hope a resolution is possible in the near term.
I read though the post at the NSIDC news page (reproduced by Anthony above), and found this passage to be most troubling:
“Some people might ask why we don’t simply switch to the EOS AMSR-E sensor. AMSR-E is a newer and more accurate passive microwave sensor. However, we do not use AMSR-E data in our analysis because it is not consistent with our historical data. Thus, while AMSR-E gives us greater accuracy and more confidence on current sea ice conditions, it actually provides less accuracy on the long-term changes over the past thirty years. There is a balance between being as accurate as possible at any given moment and being as consistent as possible through long time periods. Our main scientific focus is on the long-term changes in Arctic sea ice. With that in mind, we have chosen to continue using the SSM/I sensor, which provides the longest record of Arctic sea ice extent.”
I really don’t understand this. It makes NO sense to continue to use substandard instrumentation when a more reliable and accurate sensors are available. Does this mean that the absolute numbers associated with sea ice extent and area are not meaningful? I suppose it’s like having a miscalibrated thermometer which reads 75 F when it’s really 65 F. You can’t change it for a more accurate instrument because your long term trends are biased by the miscalibrated thermometer! At this point, if the SSM/I is dead, then they may have no choice…
If scientists scrutinized a data anomaly as if it were a tiny mole beginning to look suspicious, this would not have happened over such a long period of time. However, I do not encourage the science community to hold onto data before publishing it raw. We are all well-trained in detecting differences and have no sponsor to please. While some of us have our pet beliefs and agendas, this is balanced out by other common folk who remain delightfully curious and questioning. So dear Dr. Meier, please do not decide to “scrub, rinse, and repeat” before you post raw data. You need us. We work for very low wages and most have medical coverage elsewhere.
ok dr meier you earned a bonus point of respect with me with your forthcoming explanation of the satellite error and the reasons for using this data…i would like to hear more about the accuracy of the techniques as to 15% sea ice extent and watts up with using this cutoff and how is it determined…i also think dr meier’s explanation vindicates there was something to blog about…excellent work mr watts…
Ray (22:42:36) :
It’s not that I like to repeat myself but I did question the december flatness (and slight drop) several times already. In view of this important piece of information, will they review, as a minimum, the past 6 months data?
And the answers still the same, the flatness was real and isn’t even unusual at this time of year. There are several independent sources for that.
REPLY: I’m sure they’ll go over everything, because much of the data is now in question. – Anthony
“Much of the data” isn’t in question, more hyperbole like your headline, where does the quotation about “catastrophic failure” come from? At least two organizations are continuing to use the SSM/I data without obvious difficulty so “catastrophic” is obviously an exaggeration.
REPLY: You know Phil, you really ought to read more carefully before you jump to conclusions and make accusations. The headline is directly from NSIDC’s own article, and is in the body of text here, which is why it’s in quotation marks. For an Princeton academic you should know better. An apology is in order. – Anthony
Guess that explains why the site doesn’t appear to be being updated since they ‘corrected’ the initial misreporting.
Sad news. Maybe we can use Stimulus funds to put another Bird up. 🙂
Also explains why the sea ice extent they reported appears to have mirrored 2008 so much 500K makes quite a difference in the chart.