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.


The Quality Assurance Framework for Earth Observation consists of seven distinct key guidelines linked through an overarching document the QA4EO Principles. QA4EO activities and tasks are outlined in the QA4EO Implementation Plan.

Guideline QA4EO-QAEO-GEN-DQK-002 (A guide to content of a documentary procedure to meet the Quality Assurance requirements of GEO') is essentially the core requirement for QA4EO. If processes are carried out in full compliance of this fundamental guide, a user can have confidence in any resultant output. QA4EO-QAEO-GEN-DQK-002 provides the template to guide the user through the process, aided by the other six key guidelines for specific technical details, but in principle this guide provides all the information needed to be compliant.

In considering issues of interoperability and international harmonisation within any specific GEO community it is often helpful to start with a review of generic activities and from these define key requirements that drive the QA process. For example, in the space sector all derived information products originate from a measurement made by a satellite sensor. Thus, a set of key activities for every sensor could be defined for implementation during its development and operation.

Guideline QA4EO-QAEO-GEN-DQK-001 provides this satellite-based example to illustrate the process. This example shows how the top level requirements drive the need for community references, indicate critical generic deliverables for bias evaluation through comparisons and act as a starting point for more detailed technical procedures to underpin the top level requirements.

Official QA4EO Documentation

  • Key Documents
    Title Description
    QA4EO Guide QA4EO user guide providing background about QA4EO and implementation
    QA4EO Principles Background to QA4EO and key guidelines
    QA4EO Implementation Plan Outline of QA4EO activities and tasks
  • Guidelines
    Identifier Description
    QA4EO-QAEO-GEN-DQK-001 A guide to establish a Quality Indicator on a satellite sensor derived data product
    QA4EO-QAEO-GEN-DQK-002 A guide to content of a documentary procedure to meet the Quality Assurance requirements of CEOS
    QA4EO-QAEO-GEN-DQK-003 A guide to 'reference standards' in support of Quality Assurance requirements of QA4EO
    QA4EO-QAEO-GEN-DQK-004 A guide to comparisons - organisation, operation and analysis to establish measurement equivalence to underpin the Quality Assurance requirements of QA4EO
    QA4EO-QAEO-GEN-DQK-005 A guide to establishing validated models, algorithms and software to underpin the Quality Assurance requirements of QA4EO
    QA4EO-QAEO-GEN-DQK-006 A guide to expression of uncertainty of measurements
    QA4EO-QAEO-GEN-DQK-007 A guide to establishing quantitative evidence of traceability to underpin the Quality Assurance requirements of QA4EO

Practical guides to a metrological approach for EO

  • Practical guides to a metrological approach for EO

    These guides were produced in the frame of the ESA project IDEAS-QA4EO, and based on work in several other collaborative projects, as practical guides to support the development of a robust uncertainty budget for Earth observation measurements.

    Title Description
    Executive summary Introduces the guides
    Metrology document Provides the theoretical basis of a metrological approach to uncertainties and comparisons
    Process document Step-by-step guidance on implementing a metrological approach to uncertainty analysis
    A guide to comparisons Best practices for EO comparisons, based on guidelines established by metrology institutes for MRA comparisons
    Toolkit introduction Introduction to the CoMET tools to support uncertainty analysis for Earth observation data sets

Community-specific guidelines

  • Community-specific guidelines
    Identifier Description
    QA4EO-WGCV-IVO-CLP-001 Use of the Moon for in-flight calibration stability monitoring
    QA4EO-WGCV-IVO-CLP-002 Protocol for the CEOS WGCV Comparison of techniques/instruments used for surface IR radiance/brightness temperature measurements
    QA4EO-WGCV-IVO-CLP-003 A procedure for establishing a 'land-based' reference standard test-site
    QA4EO-WGCV-IVO-CLP-004 A best practice guide to land 'test-site' characterisation
    QA4EO-WGCV-IVO-CLP-005 Guidelines for the identification and set-up of new systems complying with requirements for satellite ocean color applications
    QA4EO-WGCV-IVO-CLP-006 Methodologies that should be applied to determine immersion factors for both radiance and irradiance underwater sensors
    QA4EO-WGCV-IVO-CLP-007 Absolute Calibration using Rayleigh Scattering
    QA4EO-WGCV-IVO-CLP-008 Protocol for the CEOS WGCV pilot Comparison of techniques/instruments used for vicarious calibration of land surface imaging through a ground reference standard test site

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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