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.

Quality Indicators

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.

Early career earth observation scientists



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:

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.

The core concepts are explained in more detail on the FIDUCEO website, and in an NPL eLearning Course on Climate Data Records from Satellites.

See the QA4EO Documents page for more.

Contact Us

We welcome feedback, so please contact the QA4EO team with ideas for new material, links to your own relevant activities, corrections, or to ask questions.

We’re also keen to learn about outcomes of these ideas in practice. Let us know how you got on.

The Quality Assurance Framework for Earth Observation (QA4EO) was established and endorsed by the Committee on Earth Observation Satellites (CEOS) to meet a requirement identified by the Group on Earth Observations (GEO) to enable interoperability and quality assessment of earth observation data.

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.

The National Physical Laboratory is committed to protecting and respecting your privacy. See privacy statement.