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Data Error: Arctic Sea Ice Extent Underestimated by 500,000 Sq Km
National Snow and Ice Data Center, 18th February 2009: ‘Satellite sensor errors cause data outage’
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.
The final paragraph is interesting:
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.
February 22nd, 2009 at 4:37 am
[...] Climate Research News [...]
February 22nd, 2009 at 10:52 am
They want to be consistent with the Gore agenda. That’s nice of them to admit.
February 25th, 2009 at 11:21 pm
There has to more to it than wanting to be “consistent with our historical data”. It seems like it would be pretty easy to provide an equation that relates the AMSR-E data to the old data, so that you could still use the new sensors to track the “long-term changes”. It’s sort of like using Celcius and Fehrenheit. As long as you know their relationship, it doesn’t matter if the numbers are different.
March 11th, 2009 at 1:44 am
Just like how they only measure ice of a certain thickness, totally excluding the rapid growth of new forming, thinner ice.
December 8th, 2009 at 1:08 pm
Bryan,
Of course you only measure ice of certain thickness! Pack ice is very different than the thinner ice, and you CAN NOT equate the two. And yes sometimes you can get rapid growth of thin ice in a particular year, butthen it ALL can be gone come summer. Whereas pack ice takes a lot more thermal energy to melt.