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.

Tools for experienced Earth Observation scientists


When QA4EO was endorsed as a principle in 2010, it provided high-level guidelines for how it was to be applied in practice. Over the following decade, multiple projects successfully implement these principles in a wide range of Earth observation applications. Terms such as ‘Fundamental Data Records (FDRs)’ for level 1 satellite products, ‘Thematic Data Products (TDPs)’ for higher level satellite products (geophysical quantities) and ‘Fiducial Reference Measurements (FRMs)’ for the sub-orbital observations used in satellite calibration and validation, were introduced to identify records that introduced uncertainty analysis and comparison methodologies based on QA4EO principles. Here we have consolidated best practices from several of these projects into a new set of guidance documents, tools and case studies. These documents offer guidance on effective implementation of metrological QA4EO principles into your Earth observation projects.


A fundamental data record (FDR) is a record, of sufficient duration for its application, of uncertainty-quantified sensor observations calibrated to physical units and located in time and space, together with all ancillary and lower-level instrument data used to calibrate and locate the observations and to estimate uncertainty.

Generally, FDRs will be geolocated level 1 products. The FDR is a record of the physical quantity measured by the sensor. Although some applications in reanalyses ingest level 1 products, for many applications FDRs will be used to generate TDPs.

A thematic data product (TDP) is a record, of sufficient duration for its application, of uncertainty-quantified retrieved values of a geophysical variable, along with all ancillary data used in retrieval and uncertainty estimation.

TDPs are higher level products that have been processed from FDRs, through algorithms which also often combine information from another FDR (e.g., from other satellite sensors) or from external information (such as reanalysis models).

Fiducial reference measurements (FRMs) are a suite of independent, fully characterised, and traceable sub-orbital measurements that follow the guidelines outlined by the GEO/CEOS Quality Assurance framework for Earth Observation (QA4EO) and have value for space-based observations.

FDR and TDP definitions are sourced from the FIDUCEO project FCDR and CDR definitions. The FRM definition comes from ESA.

Executive Summary

Step 1 - Executive summary

  • Executive Summary
    Title Description
    Executive Summary Overview of how to apply metrological principles to FDRs, TDPs and FRMs

Step 2 - More detailed information

Step 3 - Further material

Further documents, including the original QA4EO guidelines are available in Documents.

Step 4 - Further help

Sources for advice on implementing QA4EO principles for your project.

UK National Physical Laboratory (NPL): Earth observation, climate and optical

NPL helps improve the quality of data collected from Earth observation systems and satellites, so organisations can use Earth observation data with confidence.

European Metrology Network for Climate and Ocean Observation

Building partnerships between measurement specialists across Europe and climate & ocean observation communities, to promote metrological best practice in Europe and beyond.

Step 5 - 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 get 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.

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