Work carried out and key findings:
• Conceptualising, formalising, demonstrating and publishing a complete set of methodologies for metrology of “level 1” Earth observations (used in FIDUCEO for FCDRs, but generally applicable). Specifically, the concepts and methodologies developed are: satellite-relevant metrology vocabulary; measurement-function centred analysis of uncertainty; traceable, formalised documentation of error covariance information; mathematics for deriving user-oriented, summary uncertainty information; and a standard product format enabling exploitation by level-1 users (easyFCDR).
• Demonstrating this set of metrology methodologies for the four target FCDRs, all of which are successfully “uncertainty-quantified” and freely available in the new standard formats.
• Disseminating the methodologies through the FIDUCEO web site, including attractive, well-read blogs, online “cookbook” video tutorials and training materials, two open FIDUCEO workshops (with international attendance), training at two additional events at the request of the European Space Agency, targeted presentation at the 2017 EUMETSAT conference, presentation at many other conferences, input into the CEOS & CGMS networks of space agencies via the joint Working Group on Climate, and publication of an open access overview in a key metrology journal (which was downloaded >1400 times within 5 months of publication) as well as further detailed scientific publications.
• Long term FCDRs across many sensors need to be carefully and sensitively aligned. In FIDUCEO, this process of “harmonisation” is tackled be re-calibrating sensor radiances consistently, used advanced mathematical and computational techniques to derive new calibration parameters. The science of harmonisation differs across sensors because of their individual characteristics and scientific opportunities. For example, harmonisation of the Meteosat visible FCDRs involved innovative retrieval of the process of changing responsivity of the instruments as they degraded in time, whereas for HIRS the main challenge is using coincident observations to “daisy chain” the calibration along the series. The metrological principles underpinning harmonisation are in common for all the sensors. Harmonisation was a harder challenge than foreseen: while the Meteosat harmonisation has succeeded fully as hoped, various restrictions on the achieved harmonisation apply for the other series.
• Harmonisation tools have been developed and are available for re-use and further development. These include satellite-satellite match-up systems (to find the coincident observations needed), advanced solvers to find the harmonisation solution that best reconciles the calibration of a series of sensors, and tools to work with the inputs to and outputs from the solvers. A further freely available tool propagates uncertainty in easyFCDRs to a user-specified retrieval of a geophysical variable of interest.
•Four demonstration CDRs were derived from the FCDRs, addressing atmospheric humidity, aerosol, albedo and surface water temperatures (ST). All of these apply the metrological principle of propagation of uncertainty from the easyFCDR to the CDR, and give users advanced uncertainty information. Additionally, the ST CDR was experimentally produced in ensemble form, using innovative methods to ensure that the spread across the 10 members represents ST uncertainty at all scales and correctly estimates sources of uncertainty that could not otherwise be captured.
