Analysis of current validation practices in Europe for space-based climate data records of essential climate variables

• Both validation capacity and validation requirements determine the validation process.
• The independence level of reference data and external reviewers has to be assessed.
• Each validation step should be documented to enable traceability.
• The quality indicators reflect the quality of validation processes, not of products.

The Climate Data Records (CDRs) of Essential Climate Variables (ECVs) that are based on satellite observations need to be precisely described. In particular, when these products are delivered to end-users, the error characteristics information and how this information is obtained (e.g., through a validation process) need to be documented. Such validation information is intended to help end-users understanding to what extent the product is suitable for their specific applications. Based on how different European initiatives approached the validation of CDR and ECV products, we reviewed several aspects of the current validation practices. Based on the analysis of current practices, essentials of validation are discussed. A generic validation process is subsequently proposed, together with a quality indicator.