It is critical that data and derived products are easily accessible in an open manner and have associated with them an indicator of quality traceable to reference standards (preferably SI) so users can assess suitability for their applications, i.e. the ‘fitness for purpose’.
A QI shall be based on documented and quantifiable assessments of evidence demonstrating the level of traceability to internationally agreed (where possible SI) reference standards.
A Quality Indicator (QI) shall provide sufficient information to allow all users to readily evaluate the fitness for purpose of Earth observation data or derived products.
This page describes training materials provided to help you to learn basic principles of metrology and how these apply to Earth observation. It provides a training pathway to work through, although we strongly recommend ‘learning by doing’ and working, in parallel, on real examples.
Basic metrological principles
Basic principles of metrology are described in material produced by the International Bureau of Weights and Measures (BIPM) and the world’s metrology institutes.
See, for example:
- The BIPM website for information about world metrology and access to the GUM and its supplements.
- NPL provides free introductory uncertainty material with 'Measurement uncertainty explained', along with paid-for introductory courses at: e-Learning courses - NPL Training.
- NIST online materials on principles of metrology and uncertainty and the NIST uncertainty machine.
- UKAS (United Kingdom Accreditation Service) provides an introductory guide to uncertainty as the M3003 document. This is written for people doing laboratory-based metrology; but covers the basic ideas (except for error covariance) very well.
- The NPL coordinated EMPIR EMUE project produced a compendium of examples of Good Practice in measurement uncertainty
- A good introductory textbook to uncertainty analysis that follows the GUM terminology in a very accessible manner, is 'An introduction to uncertainty in measurement', by Les Kirkup and Bob Frenkel.
Introductory Uncertainty Analysis material with a (radiometric) Earth Observation focus
The MetEOC website provides introductory material on uncertainty analysis. The examples relate mostly to radiometric FRMs (in situ observations with visible and shortwave infrared optical detectors).
There is a downloadable PDF of a textbook and videos of the course as it was taught live in February 2015. The video on the law of propagation of uncertainties is particularly helpful as an introduction to both the GUM approach to uncertainty analysis and the basics of error correlation structures.
The same material has also been collated into an NPL eLearning course on Uncertainty analysis for Earth Observation.
A metrological approach to FRMs, FDRs and TDPs
The Executive Summary developed for this QA4EO website introduces application of metrology to FRMs, FDRs and TDPs.
See the QA4EO Documents page for more.
This website and the metrological principles documents it hosts were developed in the frame of the Instrument Data Quality Evaluation and Assessment Service - Quality Assurance for Earth Observation (IDEAS-QA4EO) contract funded by ESA-ESRIN (n. 4000128960/19/I-NS), and builds on the work of previous projects, see Acknowledgements.