Acoustic pulses in the atmosphere: An outdoor teaching laboratory.
For the past two years, the Penn State Acoustic Data Measurements and Analysis course has incorporated several outdoor‐sound exercises. One of these exercises is particularly amenable to illustrating concepts in acoustic propagation, signal design, and signal detection. Using relatively inexpensive hardware, student‐designed pulse sequences are transmitted, received, and recorded in various outdoor environments. The advantages and disadvantages of large‐bandwidth pulses are readily apparent. The students can perform replica correlation or matched filter processing and compare the achieved results to theoretical performance. The effects of the transmitting transducer on pulse shape are seen easily. Variability in the atmospheric propagation path, multipath, and upwind/downwind effects can be demonstrated as well as the impact of ambient noise on pulse detection. In addition, pulses can be reflected from moving objects (buses, for example) either for analyzing Doppler shift or for experimenting with Doppler‐tolerant detection. Waveform types range from simple sinusoidal pulses to frequency‐modulated pulses and frequency‐ or phase‐shift coded maximum‐length sequences to reproductions of animal vocalizations. In the fall of 2010, 40 students participated in this exercise: 20 resident students and 20 distance‐education students.