You Can't Handle the Truth

Why American Universities offer a Ph.D. Degree in Analytical Chemistry

During the first day of my Analytical Chemistry and Instrumentation and Measurement courses my students and I cover the following facts:

• Economics is the study of Wealth
• Art is the study of Membership
• Politics is the study of Power
• Religion is the study of Values
• Science is the study of Truth

and we review the following definitions:

• Accuracy is how close measurements are to the Truth
• Precision is how close measurements are to Each Other

So the rest of the courses are conceptually simple:

Design and make measurements with the utmost care such that the results represent our current best understanding of the Truth.

This is why my professional sensibilities have been so bruised by the National Snow and Ice Data Center (NSIDC) and their February 18, 2009 comments concerning the drifting calibration of a sensor measuring the extent of Arctic Sea Ice.

The NSIDC publishes a daily image of the Arctic Sea Ice collected through the process below:

"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 modeled data is compared to independent measurements made by the NASA Earth Observing System Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor. Beginning in early January 2009, the SSM/I data measured a rapidly shrinking amount of sea ice (500,000 square kilometers (193,000 square miles) an area roughly equal to the size of California). After a closer look at the data, NSIDC discovered the SSM/I sensor had experienced calibration drift and was generating values that were low by close to 200,000 square miles.

I'm not surprised by calibration errors: measurement specialists are trained to find and correct them. What I am surprised by is the statement from the NSIDC concerning their use of a measurement instrument that incorporates a sensor with known baseline drift problems:

"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."

So the measurement folks at NSIDC have chosen "precision" over "accuracy", or as I tell my freshmen, choosing "the wrong answer consistently" over "the truth".

I wouldn't mind so much if I could simply pen a note to some obscure scientific journal reminding folks of the basics, but the problem is that the Political/Power folks use this data to prove the Arctic has lost snow and ice cover the size of California in as little as one month. I sure hope everybody knows how to swim.