The aim of this WP is to develop and demonstrate techniques for in situ high accuracy (approximately 10^-7) air refractive index determination with factory-sized volumes; three different innovative thermometer prototypes will be developed and tested.

In Task 3.1, we will develop a prototype spectroscopic thermometer dedicated to effective temperature measurement in industrial conditions along an optical path up to 50 m, based on the temperature dependence of absorption spectrum line strengths of molecular oxygen in air.

In Task 3.2, we will develop acoustic thermometers dedicated to effective temperature measurement in industrial conditions along an optical path up to 50 m. Two prototypes based on the temperature dependence of the speed of propagation of an acoustic wave in air will be produced, one based on pulses (‘PTOF’ system), the other based on the propagation of continuous wave audio signals (‘CWP’ system).

In Task 3.3, we will  validate and compare the 3 acoustic and spectroscopic prototype thermometers from Tasks 3.1 and 3.2.