Stability and Accuracy Requirements for Satellite Remote Sensing Instrumentation for Global Climate Change Monitoring

To assess the impact of anthropogenic effects on global climate and to quantitatively distinguish them from natural effects is a daunting scientific task. To meet this challenge, satellite instruments, for example, must be capable of observing atmospheric temperature trends as small as 0.1 C/decade, ozone changes as small as 1%/decade, and variations in the sun’s output as small as 0.1%/decade. The importance of understanding and predicting climate variation and change has increased significantly in the last decade. In 2001, the White House requested the National Academy of Sciences (NAS) National Research Council (NRC) (NRC, 2001a) to review the uncertainties in climate change science. One of the three key recommendations from the NRC’s report is to “ensure the existence of a longterm monitoring system that provides a more definitive observational foundation to evaluate decadalto century-scale changes, including observations of key state variables and more comprehensive regional measurements”. To accelerate Federal research and reduce uncertainties in climate-change science, in June 2001, President George W. Bush created the Climate Change Research Initiative (CCRI). To develop recommendations for improving the calibration of satellite instruments to meet the challenge of measuring global climate change, the National Institute of Standards and Technology (NIST), National Polar-orbiting Operational Environmental Satellite System-Integrated Program Office (NPOESS-IPO), National Oceanic and Atmospheric Administration (NOAA), and National Aeronautics and Space Administration (NASA) organized a workshop at the University of Maryland Inn and Conference Center, College Park, MD, November 12-14, 2002. Some 75 scientists, including researchers who develop and analyze long-term data sets from satellites, experts in the field of satellite instrument calibration, and physicists working on state of the art calibration sources and standards, participated in the workshop. Workshop activities consisted of keynote papers, invited presentations, breakout groups, and preparation of draft input for a workshop report. The keynote papers and invited presentations provide extensive background information on issues discussed at the workshop and are posted on the NIST web-site: http://physics.nist.gov/Divisions/Div844/global/mgc c.html. (Please Note: To access this site, you have to input user name: mgccoutline, and password: div844mgcc) ABSTRACT: In the remote sensing community, stability and accuracy are two critical terms that need to be used in a consistent and clear way for their use to be of maximum benefit. Their definitions in combination with the vocabulary of the ISO Guide on uncertainty analysis have been applied to long time series measurements using satellite instruments for climate monitoring. Based on the definitions of these terms, requirements have been developed for satellite instrumentation at a calibration workshop on November 12 – 14, 2002 organized by NIST, NOAA, NPOESS IPO and NASA. The background analyses that lead to some of these requirements are discussed.