A student designed experiment measuring the speed of sound as a function of altitude

TL;DR

This study demonstrates how inexpensive equipment and Bayesian analysis can be used by students to accurately measure the speed of sound at high altitudes, providing insights into atmospheric composition.

Contribution

It introduces a cost-effective experimental setup and Bayesian data analysis for measuring the speed of sound as a function of altitude in a student-led project.

Findings

Achieved accurate speed of sound measurements at 101,000 feet altitude.

Set limits on atmospheric molecular abundances using sound speed data.

Validated the effectiveness of inexpensive equipment and Bayesian methods in high-altitude experiments.

Abstract

Relatively inexpensive and readily commercially available equipment (such as digital recorders, MP3 portable speakers and tie-pin microphones), allowed a team of students from McNeese State University to measure the speed of sound in the atmosphere as a function of altitude. The experiment was carried as a payload (in the context of a NASA funded student program called La-ACES) on a high altitude balloon that reached a maximum altitude of 101,000 feet. Not withstanding substantial environmental noise, our particular experimental design allowed for the filtering of the signal out of the noise, thus achieving remarkable accuracy and precision. The speed of sound measurement was then used to set limits on the abundances of the main molecular components of the atmosphere (diatomic nitrogen and oxygen). Bayesian analysis was used to set meaningful values on the uncertainty of our limits. It is our experience that students find intutive and appealing this type of probability method.