Experimental investigations of ultrasound speed and absorption in the Martian atmosphere

Future Martian missions might carry acoustic anemometer, microphone, or ultrasound inspector. These Martian acoustic probes all need to be specifically designed to adapt to the tenuous Martian atmosphere. To aid the design, experiments have been carried out to measure the sound speeds and the absorption coefficients of ultrasound pulses in a vacuum chamber filled with 600–1000 Pa CO
2
gas. Results show that the sound speed barely changes with the gas pressure. And the average speed in the 288 K air and CO
2
are 340.2 and 269.1 m/s. The wave attenuation in the 600–1000 Pa CO
2
is stronger than that of the air. And the absorption coefficient in the air increases with the dropping pressure. However, the variation between the absorption coefficient and the gas pressure is very complicated for 21–40 kHz pulses in the CO
2
.