Metrological traceability for the absolute gravity Italian network

The Absolute Gravity Italian Network project aims to update the Italian gravity network that nowadays is framed to IGSN71, established in 1971. The focal point of the project is to define a new reference for gravity with absolute gravity observations performed according to the international standardised methodology detailed in the document “CCM-IAG Strategy for Metrology in Absolute Gravimetry” (2015). IAG resolution No. 2 and subsequent, moreover establish the need to satisfy the metrological traceability also for Absolute Gravity measurements. This can be exploited by different methods such as reference sites, international comparisons of absolute gravimeters and calibration by comparison. Measurements have been performed in appropriate sites distributed across the Italian country. The collected and validated data will be stored in an open database, as the absolute gravity database maintained by the Bureau Gravimétrique International/Bundesamt fuer Kartographie und Geodaesie when will be operative, contributing to feed the new International Terrestrial Gravity Reference System. All the gravimeters used in the measurements participated to the international comparisons organised by CCM and/or EURAMET TC-M obtaining compatible results. However, in order to validate the results and to ensure traceability to the SI, additional comparisons between the absolute gravimeters used in the measurements have been performed just before the measurement campaign. The primary Italian reference instrument is the absolute gravimeter IMGC-02, developed and maintained by INRiM with an expanded measurement uncertainty of 8.5 μGal. The comparison sites are both located at INRiM and are provided with solid basements that guarantee good measurement repeatability and low floor noise which could ensure the final uncertainty. This paper shows the results of these measurements.