Post-doctoral researcher in geophysics and instrumentation
Infrasound is one technology of the International Monitoring System (IMS) for compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The data from this global network is also used by a wide scientific community for civil and scientific applications (natural hazard monitoring, weather prediction, climate change). The IMS infrasound network is unique by its global coverage, data quality and continuity (Marty, 2019). However, the environmental conditions at monitoring stations are far from those found in the laboratory. Extremes of temperature and humidity and a harsh geographical environment aggravate the measurements and additional challenges for understanding and assuring the ongoing performance of the sensors. Furthermore, measurements of infrasound phenomena of either natural or man-made origins are not yet covered by measurement standards. The derived advanced products with potentially high environmental and societal impacts are lacking of traceability of measurement to the International System of units (SI), thus compromising reliability and wide acceptance.
The project "Metrology for low-frequency sound and vibration" funded by the EURAMET, aims at developing improved low-frequency acoustic instrumentation, calibration standards and method by extending the frequency range for traceable measurements from 100 s period to few Hz. The EMPIR initiative enables the establishment of a long-term measurement infrastructure, in connection with the international metrology organization, linking transnational monitoring networks in collaboration with user communities. This includes the development of the required standards and calibration methods for validation and dissemination as well as on-site transfer to the actual applications at environmental measurement stations.
The objective of this post-doctoral position is to develop on-site calibration methods for application at environmental monitoring stations. For this purpose, long-term continuous records from well identified sources detected in the broadband coherent background noise (between 0.01 Hz and 5 Hz) (e.g. volcanoes, microbaroms generated by the interaction of ocean gravity waves) will be used to develop in-situ calibration techniques (e.g. Gabrielson, 2011). Series of field experiments will be conducted at the German IMS station and thanks to the ARISE infrastructure facilities at the multi-technology Haute-Provence observatory (http://arise-project.eu). The measurement stability will be evaluated through various installation conditions and environmental exposures, leading to enhanced knowledge of system performance in operational conditions. These calibration experiments aim at improving the overall performance of the monitoring station through the establishment of primary measurement standards, and the application of measurement uncertainty principles. The resulting calibration capability will underpin new measurement services, will be embodied in ISO standards, and will bring key metrology concepts and recommendations for microbarometer deployment strategies.
How to apply
Dr. Alexis Le Pichon