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?
gary gulrud (09:57:57) :
> OT: Volcanism Blog and Fresh Bilge report renewed eruption of Chaiten.
Something else made me check, what was that? Oh well.
Useful links:
http://eruptions.wordpress.com/
http://volcanism.wordpress.com/ says:
There seems little doubt that what occurred today was a major partial dome collapse, generating pyroclastic flows that penetrated a long way south along the Chaitén river valley, almost reaching the town itself. A collapse such as this is a process rather than an event, and further collapses of the structure of the dome(s), along with the release of overpressurized gases, is continuing to generate further debris flows along the length of the valley. Hence the continuing danger to the town of Chaitén referred to by ONEMI in the bulletin above.
Well, if we can’t watch Sea Ice….
Just a thought for the producers and keepers of data:
Where news about data and its global warming ‘effects’ have been released to the press, and the data then found to be in error, why not issue a press release about the error, and strongly suggest a published correction? Good journalists may well correct the record in print.
Was the data from the DMSP satellite feeding the new “Ocean in Google Earth” feature that was just noted here on 2 Feb 2009, or did the NSIDC use other sources?
http://nsidc.org/news/press/20090202_GoogleEarth.html
Phil needs a lot more than just a timeout, he needs a little common sense to go with a dash of humility but I expect that is not going to happen in this lifetime.
Anthony,
Good job and thank you.
It makes me wonder how long this has been going on (signal degradation) and if it would have ever come to light if you hadn’t asked a few simple questions. Even I, as a lowly novice, saw some “unconventional” anomalies in the daily graph.
Not implying a conspiracy, just sloppy work and complacency. It almost seems as if many Alarmists so wish that the ice will melt that their minds are conditioned to simply accept what they wish to see without question.
Trust but Verify…………
the global sea ice trend that was flat for most of the time and started a downwards trend only after 2001.
now it has again reached it’s 1979-2000 average (adding the 500000 km^2).
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/global.daily.ice.area.withtrend.jpg
why is this important ?
firstly, it is generally important to look at the whole picture.
but more importantly, in the past, the AGW crowd decided only to focus on the northern hemisphere anomaly while claiming the antarctic record sea-ice was some irregular local behaviour.
now, as some people in the AGW crowd appear to try to regard the antarctic no longer as an outlier, if may become difficult for them to ignore 1/2 of the planet.
Karl Heuer (06:32:52) : wrote:
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.
—————————————————-
The people at Cryosphere today should have known exactly where George Will’s information was coming from since, right beneath their George Will comment, they have a link to the following article (excerpted) here:
“One important detail about the article in the Daily Tech is that the author is comparing
the GLOBAL sea ice area from December 31, 2008 to same variable for December 31,
1979. In the context of climate change, GLOBAL sea ice area may not be the most
relevant indicator.”
Any 5-year old with a computer screen and a ruler can go to Cryosphere Today and see that global sea ice areas in December 1979 and December 2008 are indistinguishable.
Since the George Will article actually came out on February 15th, I doubt that he could have done the comparisons of that date without using a crystal ball during the drafting of the piece.
Yet the Cryosphere Today people still disingenuously show the 1979 – 2000 mean, when they could now show the full 30 year mean as the comparator. Also, as I gather from reading above in this thread, data is available going back to 1972.
For people with an aparent concern for the planet, they sure as heck seem to prefer less ice over more ice. The monetary dichotomy of cognitive dissonance ??
Three things really stand out for me on this:
1) Once again the quality of data in what has to be the world’s hottest debate is suspect, with an apparent lack of quality control. A key missing point, just like the “warmest October on record” seems to be the absence of a common sense review. Its like taking a steadfast view that “the numbers never lie’ without considering that the input data may not be entirely correct. This seems to be a systematic problem in the climate world.
2) It highlights the irony of Dr Meier’s wondering whether this was something worth blogging about. This example highlights the necessity of someone to review these types of data publications (dare I say audit them?), before, as you rightly pointed out Anthony, the press or others make major issues out of completely incorrect data and conclusions.
3) And this point, which I just don’t get: the use of SSM/I sensor compared to EOS AMSR-E sensor data. The explanation given appears to make sense on only on the first reading. What Dr Meier basically is saying is that consistency is more important than accuracy. It appears though that SSM/I sensor data is a bit dodgy, but presumably it is at least consistently dodgy! This is almost unbelievable. The simple fact is that both consistency and accuracy are important, which means that both data sources need to be tracked and compared or calibrated.
Would this be more difficult or expensive? I don’t know and don’t care. Unless tracking the ice is unimportant, then the inconvenience and cost are irrelevant. Tracking two data sources also serves as a cross-check, which would help avert the type of embarrassing data error that has occurred.
“philincalifornia (15:42:30) :
For people with an aparent concern for the planet, they sure as heck seem to prefer less ice over more ice. The monetary dichotomy of cognitive dissonance ??”
Maybe if they got paid a certain $ amount per km2 counted, then we’d see the sea ice grow!
Please have a look at this comparison between AMSRE (JAXA site) and SSM/I (NSIDC) This compares monthly averages back to 2002. In general the AMSRE data is smaller than the NSIDC and the only significant time it is larger is in Sept 2008 when it is 170,000 sq km larger. A difference of 3.5% larger compared to AMSRE area at that time.
http://img16.imageshack.us/img16/9782/ssmiamsrerz8.jpg
There seems to be no significant drift visible in earlier data. There is an obvious difference in the algorithms used to genereate the 15% sea ice areas.
There are many warnings on all pages that reference the real time data e.g.
“Daily images are also available. Monthly averages are considered more accurate indicators of overall trends. Please read Image Derivation and Interpretation Resources to understand the uses and limitations of these figures”
To see a truly amazing video of sea ice download this AVI showing the whole polar cap in motion (Very big file but worth it!)
http://polynya.gsfc.nasa.gov/animations/amsr/amsr_seaice_north_89v_hdtv.avi
Mike
Meanwhile…back in the REAL world…the poor dolphins are dying from sea ice extent!
http://www.google.com/hostednews/canadianpress/article/ALeqM5gK4JcIUd16HiCSBxKRBz8vTpzBWQ
Brute (15:21:52) :
“It makes me wonder how long this has been going on (signal degradation) and if it would have ever come to light if you hadn’t asked a few simple questions. Even I, as a lowly novice, saw some “unconventional” anomalies in the daily graph.
Not implying a conspiracy, just sloppy work and complacency. It almost seems as if many Alarmists so wish that the ice will melt that their minds are conditioned to simply accept what they wish to see without question.
Trust but Verify…………”
Ain’t gunna happen. This is all just too complex and technical to verify in general, and it’s a different matter from land temps where people live, pictures can be taken of reporting stations and UHI is a comparably simple subject.
NSIDC stated sometime early February that they had noticed a decrease in ice, and attributed it to possibly being an unusual wind pattern. At around that time ice extent had dropped around half a million square kilometers below AMSR-E.
I don’t claim dishonesty, and if there is some occasional instance of incompetency or irresponsibility going on that’s not really an issue. To the last guy, I’m sure they honestly believe in AGW and that the Arctic is Gore’s canary in the coal mine, so when they saw a half mil loss in a matter of days in February, they apparently didn’t think about that being unusual or unlikely.
Likely there is only a small group of scientists working year round on all the stuff that goes into processing the telemetry from this satellite, and with the possibility that “it’s the weather” like reasons for making inferences guiding some of their work, I can’t place trust in, even hard working people who hold honest convictions.
Quality Control really seems to be the issue based on some earlier comments, especially from the insider. I would like to know how often these systems are checked and calibrated, and what is the estimated uncertainty in their measurements.
From John S. (07:52:23) comments, it seems those receiving the data have little to do with the quality of the data, and those who control the hardware/software and not giving quality an high priority:
“They monitor health and safety of the spacecraft, not the quality of the data”
Hopefully Dr Meir could enlighten us on this, although I understand he is in a difficult position if there are issues. If we need to spend more money for better climate data I am all for that. In fact, we should be doing a lot more on the measurement side than we are, as this site has exposed many such issues.
“Klimate Kip (16:25:31) :
Meanwhile…back in the REAL world…the poor dolphins are dying from sea ice extent!”
Ya just gotta wonder… if the sea ice numbers were right… would these precious dolphins have to die?
John H. (08:40:24) :
Points of interest.
1) This episode demonstrates that the “sceintific community” now includes the scrutiny conducted on the internet. Experts and novice contributors, in many fields from around the globe, are providing a level of scrutiny never seen.
This is an enormous benefit to science.
2) The lesser scrutiny provided by the establishment sceintific community and their institutions and publications have not served as an adequate check and balance.
3) The soon to be corrected sea ice trend by the NSIDC will reflect other sources which show sea ice to be nearing the average of the last 30 years contradicting the projected calamity anticipated by Hansen et al.
John,
Your post is worth repeating, so I take the liberty of reposting (part of) it. Excellent appraisal of the implications of the episode. Congrats are in order to Anthony, Dr. Meier, and all concerned, but especially to Dr. Meier for evolving from questioning the relevance of A’s “blogging” to seeing Watt’s Up as a site for developing a real dialogue about science, one that is less controlled by intellectual self-interest and tunnel vision than traditional scientific institutions tend to become….I look forward tor reading his thoughts on the problems and promises of the present situation. Crisis is almost always also opportunity, and definitely so in this instance.
Cheers,
-psi
Re: Phil’s 24 hour timout.
Couldn’t your policy have a catastrophic failure, and Phil be sentenced to 24 years?
Errrrm, have I missed an update of the site policy? Since when is giving away personally identifiable data part of the escalation strategy? Do I need to worry about my e-mail being given away in case I misbehave?
http://www.msnbc.msn.com/id/29038734/
FEB 5 2009:
“It’s warm everywhere in the Arctic. It’s anomalously warm,” said Julienne Stroeve, of the National Snow & Ice Data Center (NSIDC) in Boulder, Colo.
Both December and January have been abnormally warm months, which impacts the cyclical re-freezing of sea ice over the years, because these are “two crucial ice-growing months,” Stroeve told LiveScience.”
“While ice is still re-freezing, ice coverage area at the end of January was still 293,000 square miles (760,000 square kilometers) less than the 1979-2000 average, according to the NSIDC. This didn’t break the record low for January ice area (set in 2006), but it put January 2009 in the top six. Including this year, January ice area is declining by about 3 percent per decade, the NSIDC reported.”
http://wattsupwiththat.files.wordpress.com/2009/02/nsidc_extent_timeseries_021509.png
I guess we don’t believe this, should we believe the temperature claim either?
“If we need to spend more money for better climate data I am all for that. In fact, we should be doing a lot more on the measurement side than we are, as this site has exposed many such issues.”
The only problem with giving them more money is that they’ll just hire more alarmists to spread the hysteria…
Mike Bryant (16:50:36) :
“Klimate Kip (16:25:31) :
Meanwhile…back in the REAL world…the poor dolphins are dying from sea ice extent!”
Ya just gotta wonder… if the sea ice numbers were right… would these precious dolphins have to die?
—————————–
Somewhat reminiscent of the 500+ narwhals that died last November because they didn’t have an icebreaker in the region. Although quite tragic, I do note the irony in the fact that reports at the time described polar bears coming along and eating them !!
@ur momisugly Rathtyen (15:58:22) :
“What Dr Meier basically is saying is that consistency is more important than accuracy. It appears though that SSM/I sensor data is a bit dodgy, but presumably it is at least consistently dodgy!”
“Well, we, may have, oh, missed the, uh, bullseye, and, um, in fact we didn’t even hit the, er, target, but we did get a NICE grouping.” LOL!
@ur momisuglyKlimate Kip (16:25:31) :
Don’t forget the whales.
http://gukurup.wordpress.com/2008/11/24/arctic-whales-trapped-in-ice/
@pft (16:46:25) :
“Quality Control really seems to be the issue based on some earlier comments, especially from the insider. I would like to know how often these systems are checked and calibrated, and what is the estimated uncertainty in their measurements.”
And, as I asked above, not just how often, but HOW they are checked and calibrated, like, how do they know that the result given corresponds to what’s really there. Perhaps there’s a hint at the link provided by pkatt (13:52:53) ? …maybe here?
http://nsidc.org/data/docs/daac/nsidc0002_ssmi_seaice.gd.html#dataaccess
http://nsidc.org/data/docs/daac/nsidc0002_ssmi_seaice.gd.html#3.
Could this have anything to do with the ice increase flat lining for a week or so in mid Decembrrr?
I would really appreciate it if someone could please answer these two posts.
I am dying to know.
Thanks;
Robert Bateman (02:39:56) :
Would there be any reason to suspect that increase in cosmic rays is going to lead to increased sensor erratica and/or failure?
i.e. – should we expect spaceborne sensors to show increased rates of failure?
mercurior (03:55:13) :
i am wondering what other sensors are degrading. Could it be more of the same for other systems. There is also a possibility of feed back as well..
There is a feeling that technology is stable, when it isnt as stable as it seems.
While I appreciate the analysis of the Arctic sea ice data and the satellite sensor error discussed here, it must all be irrelevant. After all, I read the news and know the ice is shrinking dramatically because of CO2. The few polar bears we have left are stranded on the small bits of ice left as they melt away into the tropical waters of the Arctic.