A roadmap for calibration and validation

22 October 2007

The volume of data acquired by more than 50 Earth Observation satellites is increasing at an exponential rate and is providing unprecedented synoptic views of our planet. Because these satellites often use different methodologies, using data for trend analysis and environmental monitoring can be difficult, making it essential to establish globally recognised guidelines for Calibration and Validation processes.

More than 50 experts from space agencies and organisations around the world met earlier this month at the GEO/CEOS Workshop on Calibration and Validation Processes in Geneva, Switzerland, to identify and scope key elements needed to develop and implement a data quality strategy.

Calibration is the process of quantitatively defining the system responses to known, controlled signal inputs. Validation is the process of assessing, by independent means, the quality of the data products derived from the system outputs.

Workshop session
Workshop session

The workshop, hosted by the Group on Earth Observations (GEO) and ESA from 2 to 4 October, was structured around four main sessions:

  • Cal/Val site characterisation & classification
  • Satellite and in situ Cal/Val data access
  • Methodology and guidelines for Cal/Val
  • Harmonisation of quality information

At the beginning of each session, the chair presented a summary of the relevant key issues and then opened the floor for discussion.

The dialogue and recommendations will be used to achieve the ultimate goal of the Global Earth Observation System of Systems (GEOSS) for data inter-operability and inter-comparison. Prof. Jose Achache, Director, GEO Secretariat, stressed that in order for GEOSS to be fully successful, there must be calibration, validation and intercalibration between all instruments.

Group picture
Group picture

The Committee on Earth Observation Satellites (CEOS), the space contribution to GEOSS, identified the need to take a more active role in tackling these issues. The CEOS Working Group on Calibration and Validation (WGCV) established consensus within the international community that calibration, validation and quality assurance processes should be incorporated into satellite programmes in a harmonised way.

Through the session discussions, the workshop participants reached a consensus on a roadmap towards the establishment of Cal/Val best practices. These best practices will be issued as CEOS endorsed guidelines under the auspices of GEO for implementation by the agencies and will allow data to have an ascribed ‘quality’ associated with it. The guidelines will cover all aspects of the data quality from instrument characterisation to engineering calibration and geophysical validation.

Cal/Val portal
Cal/Val portal

Participants identified the need for a Cal/Val specific data policy and the allocation of the necessary resources through coordinated efforts of GEOSS members to allow the efficient implementation of these guidelines. Sufficient resources will be required to ensure the continued end-to-end operation and maintenance of a fully traceable Cal/Val system.

The first step towards harmonisation across the global Earth Observation Cal/Val community is the development of a dedicated CEOS WGCV Cal/Val portal, which will facilitate the implementation of these activities on behalf of GEOSS.

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