Enabling and demonstrating SI traceability of ECVs and climate data records: the role of a national metrology institute

The need for SI traceability to ensure integrity and trust in the Essential Climate Variables (ECVs) and the services and information derived from them, is well established. However, the means to achieve and demonstrate this in a universally-consistent manner globally and between variables, particularly for the complex bio-geophysical variables that make up many of the ECVs, is challenging.

 

National Physical Laboratory (NPL), the UK national metrology institute, has, over the last three decades, established a comprehensive research programme to extend traditional underpinning laboratory-based capabilities to meet the needs of a wide range of Earth Observation and climate applications. These have included:

• both bespoke and tailored standards together with methods for the calibration of remote-sensing instruments (including pre-flight calibration of satellite sensors),
• field measurements in the worlds Forests, Oceans, Deserts and the atmosphere
• development of metrological methods to assess and describe uncertainties, end to end (sensor to user-relevant information)
• most recently, extending to the development of a satellite to establish SI traceability from orbit as part of the ESA EarthWatch programme.

 

To build the necessary skills, capacity and trust within the community, NPL has established a close dialogue with EO/climate community experts and built international partnerships through active participation in international bodies such as CEOS & GEO. This has led to a close working relationship with ESA and other European national and international space agencies to provide metrological support across a wide range of projects.

 

This paper will discuss the criticality of SI traceability to providing trust in globally-relevant environmental & climate datasets and illustrate how it is being achieved through case studies, such as:

• the ESA Fiducial Reference Measurement (FRM) projects,
• establishment of SI-traceable reference test-sites for satellite calibration and validation
• novel infrastructure to calibrate and characterise optical satellite sensors
• and efforts to harmonise their in-flight radiometric gain.

 

NPL plays a lead role in the recently created European Metrology Network for Climate and Ocean and is keen to continue to ensure its efforts and research program address the priorities of the EO and climate community and will welcome input on future research directions.