Acoustic thermometer development for average air temperature estimation along a distance measurement optical path

 This thesis describes the development of an acoustic thermometry apparatus to estimate the mean temperature along an optical measurement path and thereby better determine the air refractive index. The measurement principle uses the time-of-flight (TOF) of an ultrasonic wave at 40 kHz. The temperature is extracted from the speed of sound using the Cramer equation which gives acoustic velocity as a function of atmospheric parameters (temperature, pression, humidity and CO2 concentration). Different methods for estimating the TOF were studied for six types of signal (single-frequency or modulated, top-hat, Gaussian and Blackman envelopes), notably intercorrelation, and a calibration procedure with respect to reference thermometers placed at intervals along the path developed. The temperature uncertainty achieved for a 10 m distance is 90 mK.

Thermometry, Acoustics, Metrology, Cross-correlation, Ultrasonics, Refractive index

PhD thesis (French) : https://theses.hal.science/tel-03997959v1/document