Use of Ultrasonic and Audio Signals to Monitor Temperature in Stratospheric Balloons

For gas temperature measurements in stratospheric balloons, traditional methods of measuring gas temperature do not work well due to radiant heating and insufficient heat transfer. To measure the gas temperature several methods of acoustic temperature measurement are being developed. One of these methods is the pitch catch method. A perceived distance pitch catch method using an ultrasonic distance sensor was proposed and tested. However, at low pressures the density of air is too low to allow sound to propagate well. This means that at a certain pressure, the ultrasonic distance sensor will not receive a reflected sound with sufficient amplitude to calculate the apparent distance accurately. Tests were conducted in a high altitude chamber to determine the accuracy of temperature measurements and the fail pressure. It was determined that the optimum configuration for this device would not allow it to function at a sufficient altitude nor give the temperature accuracy required. An alternative timing method using a piezo speaker, electret microphone, and time of flight measurements was explored. The timing method achieved a detectable signal down to 1.0kPa. Further work is being done on the timing method to increase the accuracy of the device.