WP303 – Uncertainty Budgets for FRM OCR

D-180 Report/Paper on Uncertainty Budgets of FRM4SOC FRM OCRs used to Validate Satellite OCR products

As an NMI, NPL uses the GUM consistently for the analysis of uncertainty. Indeed the NPL mathematicians who work for the Joint Committee for Guides in Metrology (which prepared the GUM and its supplements) also regularly collaborate with the scientists in the Earth Observation, Climate and Optical Group who are working on this project. For example, through our contribution in projects such as the Sentinel-2 Radiometric Uncertainty Tool and FIDUCEO as well as our own MetEOC project series, we are working to establish rigorous uncertainty analysis for Earth Observation activities involving radiative transfer, classification, and on historical and new sensors at the pixel level.
In addition these and other NPL EO projects also involve the development of training material to teach uncertainty analysis to the Earth Observation community using meaningful examples. NPL has already developed a training course on Uncertainty Analysis for EO Radiometric Instrument Calibration, and both the course text book and videos of the courses are available for free download at: http://www.meteoc.org/outreach-training.html. This course is also being developed into an online eLearning course in a project that has an ESA partner to allow thorough review by ESA.

Further modules are being developed through other projects on level 1 and higher level products as well as vicarious and test site calibration and validation of these products. Within this project we will provide some initial access to this training, either by providing introductory licences for the online training course or by hosting a live training course during LCE-1. It is worth noting that the Uncertainty Analysis for EO radiometric instrument calibration course has a specific section on the calibration of ocean colour radiometers which was based on work carried out by NPL in collaboration with LOV for BOUSSOLE and JRC for AERONET-OC.
Protocols for correctly evaluating and documenting uncertainties (Type A and B) will be supplied by NPL for all the pre experiment guidance documents for LCE-1, 2 and FICE and will be based on the GUM and our experience applying the GUM to EO related measurements. For a full end-to-end uncertainty evaluation for measurements taken by ocean colour radiometers, uncertainty estimates from each stage of the calibration and measurement process need to be combined according to the law of propagation of uncertainties:

Where y is the output parameter, u is uncertainty, uc is combined uncertainty and ∂f/∂xi or j are partial derivatives that can be thought of as sensitivity coefficients describing how the output estimate y varies with changes in the values of the input estimates (x1, x2 … xn) according to function f.
For the example of FRM4SOC, rigorous uncertainty analysis will involve documenting an SI-traceability chain for OCR measurements and combining the uncertainties from LCE-1 and LCE-2 according to the above law. Detailed discussion will also be made and documented as far as possible regarding additional uncertainties that may be added from measuring in the field. These will include the complications that the different deployment systems in use for ocean colour radiometry (e.g. in water, shipboard, autonomous profiling from floats etc.) can add to the uncertainty budgets during operational measurements.
Finally, it is likely that such a complete comparative study of the uncertainty budgets of ocean colour radiometers carried out by an NMI would be of great interest and value to the ocean colour community as a reference. Therefore considerable effort will be made by NPL to report the results of the uncertainty analysis undertaken during FRM4SOC in a relevant international peer reviewed journal.

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  • BIPM, IEC, IFCC, ISO, IUPAC, IUPAP and OIML, 1995. Guide to the Expression of Uncertainty in Measurement (Geneva, Switzerland: International Organisation for Standardisation).
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    – 2500 nm (NPL Report OP12, NPL, Teddington, UK).
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  • JCGM, 2008b. Evaluation of measurement data – Supplement 1 to the “Guide to the expression of uncertainty in measurement” – Propagation of distributions using a Monte Carlo method (JCGM, http://www.bipm.org/utils/common/documents/jcgm/JCGM_101_2008_E.pdf )
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