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?
Dr. Meier,
My perception is that you are now caught between “a rock and a hard place.” Specifically, (a) you are starting to believe that published data for which you have at least some responsibility is likely to be erroneous, and (b) people on both sides of the AGW issue are clamoring for explanations. I’ve been in a similar situation. My advice (for what it’s worth) is to take a deep breath and before making further public announcements, do the best job you can to ascertain the full extent of the problem. As you investigate the problem, you must, of course, keep your employer informed of your progress. But if you try to respond to everyone with a dog in the “AGW fight”, (a) your “wasted-time” meter will go through the roof, and (b) you’ll end up having to explain prior explanations. When you’re pretty sure you have characterized (a) the hardware/software problems, if any, and (b) the effects those problems had on published data, then and only then go public with a complete explanation. I for one would welcome such an explanation. Furthermore, as Anthony Watts via his WUWT blog/E-mails/personal communications was apparently what tipped you off to a potential problem, I believe it would be appropriate to post that explanation on WUWT.
Just an untrained observer here. As someone who works a great deal with financial data at my job, I can relate to the difficulties of getting timely, accurate data, no matter if it’s collected manually or through online feeds. There’s so much that can go wrong from point a to b to c and so on. Many of our clients complain that we don’t publish quarterly reports until weeks after the quarter end, but that’s how long it takes to review the data, contact the data source (Fidelity, Charles Schwab, etc), get it corrected, review it again, etc, etc. We do however, show up-to-the-minute data on our secure client website, and unfortunately data problems can and will happen.
I wonder if, collectively, we’ve become spoiled by the internet, the information age, and the *perception* of real-time data from all types of sources available at our fingertips. Really the only way to completely avoid publishing bad data is to release retroactively, weeks or months later if necessary, only after it’s gone through intense quality control measures. But people want it now, they don’t want to wait 3-5 weeks. So you win some, you lose some. The best compromise is to publish it now, put a disclaimer with the report, and make continued efforts to correct the data weeks or months down the line, along with written explanations of any noticable problems or changes.
I think all of us here want the same thing: the truth. This planet is the only home we’ve got, and we want, we need to know what’s going on (or watts up with) it. Thanks to Dr. Meier for posting here and keeping us updated on the issue.
Pierre Gosselin (04:14:53) :
”
“There is a balance between being as accurate as possible at any given moment and being as consistent as possible through long time periods.”
So someone please tell me if my distrust is unfair.
It is openly admitted that the data is not accurate.
”
To be fair Pierre, Could be more accurate != inaccurate.
I say well done NSIDC & Dr. Meier for the open manner in which they have conducted themselves.
I look forward to a guest post from Dr. Meier after all this is sorted out.
DaveE.
“On the main page of http://nsidc.org/arcticseaicenews/ “no data available” is still showing. That is simply the last large format image they produced.”
Anthony
Compare that to the one you saved. The downward slope is changed and the line is longer. You don’t mean that you didn’t save the last image they produced a couple days ago?
REPLY: Yes I did keep that image, you can see it here:
http://wattsupwiththat.files.wordpress.com/2009/02/nsidc_extent_timeseries_021509.png
It appears their automation is still running, producing images. As I said, that is simply the last large format image they produced. But I see your point, this image may be bookmarked. I’ll email Walt. Thanks for the spot. This is just one more reason why they should put timestamps on the images as I originally suggested. – Anthony
REPLY#2 and it is fixed now, 30 minutes later. – Anthony
John H. (08:40:24) :
“Points of interest.”
Excellent points. But meeting points 5) and 6) will be extraordinarily difficult unless “citizen science” on the order of this event presses for it. To that end we have excellent resources. This and other skeptic sites, manned by informed, intelligent people must continue to monitor institutional science for anomalies. And with coherent email campaigns to institutional supervisors and sponsors – build a record of scrutiny that nudges MSM to report “glitches” and “hiccups.”
What will be telling is if MSM covers the retractions/anomalies stories at all. They may be surprised to find an enormous public appetite for the “warming may not be man-made” angle. Reversals of this sort are fascinating to readers, evoke excitement and sell advertising. However, if sales is not their goal, we can assume that the AGW agenda is. And no submission of contrary fact will cause them to waver.
bluegrue (08:25:08) :
How about looking at what the conditions were like in 1922?
……………
What is listed as exceptional in 1922, is the rule(!) in this century.
Agreed. What those who love to trot out 1922 as an exemplar of previous arctic warming always leave out is what was happening at the other end of the arctic. In September 1921 a US-Canadian party landed on Wrangel island to try and claim it, it was unreachable due to ice for two years and all but one of the party died. The Russians also tried to get to Wrangel using ice-breakers but failed, finally made it in 1924. An ice bound Wrangel island throughout the summer is certainly not commonplace this century.
http://earthobservatory.nasa.gov/images/imagerecords/9000/9043/wrangelis_amo_2008231_lrg.jpg
Photo dated Aug 18, 2008
An investor to a company: “May I please see your latest & audited financial reports”
The company to the investor: “No – we don’t believe in external auditing – our processes was ‘peer reviewed’ some years ago and all our staff has an appropriate academic degree – we audit ourselves now”
The investor to the company: “Hmmm – but what about segregation of duties within the company – how do you make sure people don’t review their own work?”
The company to the investor: “That doesn’t matter, our boss is the smartest guy on board and he settles all disputes and pick up errors as we go along.”
The investor to the company: “See you later”.
Wait: Is this an error that doesn’t strengthen the AGW hypothesis? This is a first!
Phil. (09:31:20) :
[snip]
REPLY: Phil – no more posting privileges for you until you address your comment about the headline. – Anthony
“Much of the data” isn’t in question, more hyperbole like your headline,
That statement is correct “much of the data” is not in question.
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.
Again as per the statement that at least two other organizations are continuing to use SSM/I without obvious difficulty the sensor has not “failed catastrophically”. Therefore your source was clearly exaggerating (that their software may have failed catastrophically is another matter). Since I asked where the quote came from I was clearly not attributing it to you.
REPLY: You know Phil, you really ought to read more carefully before you jump to conclusions and make accusations.
I did neither.
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.
Because it’s a quote doesn’t mean it’s not an exaggeration.
For an Princeton academic you should know better. An apology is in order. – Anthony
As above there is nothing to apologize for, however you should apologize for releasing information given you in confidence and remove it forthwith.
So the comment’s been addressed and you can restore the posts now.
REPLY: Phil your arrogance is astounding. I’ll add that because of the source, you have no expectations of privacy. Perhaps you should find another venue. – Anthony
Richard deSousa (09:36:10)
I tend to think that any satellite that passes over one pole would have to pass over the other.
The reason to continue to use the less accurate data is the same reason we count sunspots using the old methods and not from satellite observations — that’s the consistency.
If we counted every sunspeck and fleck and tried to somehow correlate that to the 1800s’ data the comparisons between now and then would be meaningless, always subject to the additional error margin of the correlation. The same is true for the ice extent.
HOW DO THEY CALIBRATE THAT THING, ANYWAY?
negative = 50K sq km of the Sahara?
positive = 50K sq km of Teddy Kennedy’s cocktail ice for a night?
But, seriously, how do they know that their measurements correspond to reality? And how often do they run calibration tests to ensure it’s functioning properly? Or do they just do perimeter measurements to find the edge? But then that wouldn’t pick up chunks floating close together.
So, doews anyone know about that?
As for Cryosphere, a quick look shows that their “old (ssmi)” data are in as bad shape as NSIDC, however their other map versions seem OK, so presumably they are based on AMSR-E data. One wonders at which point they changed over for their area data?
Changing satellite sensors is always a difficult procedure, so it should be started as early as possible, in order to get the longest possible parallell run for calibration. Even so some of the difference between the UAH and RSS temperature records is probably due to slightly different algorithms used for a sensor change back in the early nineties.
Phil., you are a piece of work….
jorgekafkazar (09:22:58) :
“Re Dr. Steig: More transparency on his part would be a welcome improvement, but I would not automatically lump the esteemed Dr. Steig with others in this field.”
Why wouldn’t you?
He and Gavin Schmidt routinely hand each other the mic to add moderator-replies on realclimate.org.
Also on realclimate.org, he actively deletes any text (even quoted) by “Jeff Id”, so he doesn’t have to answer the challenges. “Jeff Id” is a guy who showed that by using data that’s less freakishly weighted towards one small sliver of Anarctica, even Steig’s type of data processing would produce far less backwards-from-reality-trending data.
Perhaps you’re right, though – lumping him in with the others ignores how quickly he’s apparently learned the AGWer methods of quieting dissent, and that the rectal data he presents in his papaer is likely the most separated from climate reality in recent memory.
…incidentally, that’s the same realclimate.org that makes no mention of the sensor failure. Somebody commented about it, and GS’s response was that apparently, they have enough redundancy that it won’t be a problem for further data gathering – no acknowledgement of recent erroneous data. But you knew that.
Pragmatic (10:18:06) :
Regarding my John H. (08:40:24) “Points of interest.”
I agree the 5) and 6) will be extraordinarily difficult.
But the cat is out of the bag with the global internet use. Our mainstream media is slipping tinot irrelevency in advance of backruptcy for many of them.
The real time and global benefits of the internet and widepsread scrutiny it enables will only grow.
This episode is a marvelous demonstration.
The MSM is scrambling at great speed and panic to adapt to the
effects of online participation by the masses.
They realize there is an enormous public appetite for the “warming may not be man-made” angle right along with all the other real time delivered news.
Thier problem is profit is being left out of their loop. They can’t figure out how to replace the dwindling revenue as they become less needed and relevent.
It’s all very fascinating to readers but with near limitless sources it’s increasingly hard for the MSM to be special and worthy of advertisers support.
Their agenda is quickly becoming noisy racket as their business model weakens and weakens and weakens.
mark (07:16:15) :
and add 500,000 to them, you will have a fairly unimpressive “downtrend” over the past 30 years.>
i think it is rather impressive to arrive back to the 1979-2000 average (not even need to take the 1979-2007 average…)
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.anom.jpg
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/global.daily.ice.area.withtrend.jpg
Anyone who has ever supported a long-term legacy system can appreciate Dr. Meier’s pain at facing a major data conversion. However, having acknowledged that the newer system is indeed “more accurate” than their old systems which has now failed, there is really no choice. They must do the best they can to convert the old data to match up with the new data, providing transparency on how they did it and what choices they made and why.
It is what it is. It won’t get any easier by continuing to wait.
Remember Antartica west coast volcanoes? Well, Chaiten Volcano in chilean andes (the same mountain range) is erupting again.
http://www.reuters.com/article/homepageCrisis/idUSN19510984._CH_.2400
Phil. (09:31:20) :
That’s a wonderfully ambiguous statement, bravo. Clearly, you ought to read more carefully, I wondered why NSIDC used the word “catastrophic,” as I’d be inclined to save it for something that involves a debris field. I concluded it must be catastrophic to their data gathering and analysis programs. May I jump to the conclusion you didn’t read it carefully?
Phil.
You might want to read the policy page
http://wattsupwiththat.com/policy/
In the meantime you get a 24 hour timeout
Congratulations to NSIDC for researching the error, working out the likely effect and publicising the fact that there is an error with the data – rather than simply “adjusting” it.
It is good to know that there are some honest scientists working in the climate field!
Anthony, thank you for this site. Most of the contributors discuss issues objectively, so it does not become a rant.
In particular, thank you for the recent exchanges with NSIDC and Dr Meier. The exchanges were candid, competent, and civil. And above all, the exchanges and the publication of the data (on this site) contributed to identification of a data problem.
Thank you.
Wow, I did not know I was going to stir things up like that with Phil. Sorry guys!!! (it’s not hard to say “sorry”!)
As you all know, there will be an expedition to measure the thickness of the ice at some point. If we are to believe the data on the ice area and if in fact it did not gow last december eventhough it was quite cold in Canada and Russia, could it be possible that the thickness of the ice would increase though? The globe is cooling down from Gore’s minuscule fever, surely the ice recovery must also be in the tickness as well as extent.
Everything you always wanted to know about the dmsp ssm/I
http://nsidc.org/data/docs/daac/nsidc0002_ssmi_seaice.gd.html