New primary-level soil moisture measurements with developed uncertainty budgets will be established. This will allow traceable calibration and validation of secondary measurement standards such as those based on traditional loss-on-drying and of transfer standards. Measurement institutes (e.g., National Metrology Institutes, Designated Institutes, National Measurement Laboratories) will be able to offer new or improved calibration services for existing, new, or future soil moisture measurement devices.

For soil moisture measurement there are currently unresolved issues with appropriate transfer standards and sampling methods. This project will address these issues and the transfer of the metrological chain of traceability to outdoor conditions, using new transfer standards for point-scale soil moisture sensors, in combination with improved sampling methods. In addition, transfer standards based on visible and near infrared spectral reflectance measurements for on-site calibrations will be researched. The improved metrological basis will be used for improving the CRNS methodology and should have direct impact on CRNS networks in Europe and worldwide, such as

• TERENO, Germany;
• COSMOS-UK, United Kingdom;
• COSMOS, USA;
• CosmOz, Australia;
• COSMOS-India.

The new on-field comparison campaigns (local and remote sensing), carried out within this project (see TEST FIELD SITES), will lead to the publication of good practice guides. These outputs will directly impact the scientific community dealing with soil moisture retrieval from satellites-based data, as the community is actively developing calibration and validation practices for large-scale soil moisture assessments based on point-scale soil moisture measurements on ground. The gap between the point-scale (in situ) and the kilometre-scale (satellite-based horizontal resolution) is recognized as one of the most important research gaps that must be closed. With the harmonisation and data fusion practices researched within its framework, this project will provide the metrological support required for this community.