ABSTRACT
High-fidelity measurement of sonic boom waveforms requires microphones and data acquisition hardware with flat frequency responses extending below 1 Hz. Hardware limitations can pose challenges meeting these requirements. This letter describes an engineering method involving digital pole-shift filtering that can be used in post-processing to extend effective hardware bandwidth. This approach is evaluated for sonic boom recordings from NASA's Quiet Supersonic Flights 2018 measurement campaign. Recordings of several booms at multiple measurement sites using different hardware/microphone combinations were used to design filters. Results demonstrate that the measurement-designed filters significantly reduce the mean square error between original and benchmark waveforms. Digital filter designs based on hardware manufacturer specifications also reduce error, but not as much. Residual errors after filtering, method limitations, and transferability to a launch vehicle reentry boom measurement are discussed.
ABSTRACT
An impulsive noise exposure model for outdoor military shooting ranges was created. The inputs to the model included spatial interpolation of noise exposure metrics measured from a single round of fire from a small-arms ballistic weapon. Energies from this single-shot model were spatially translated and summed to simulate multiple shooters firing multiple rounds based on the equal energy hypothesis for damage risk assessment. A validation measurement was performed, and the uncertainties associated with measurement and modeling were shown to be acceptably low. This model can predict and assess total exposures and protection measures for shooters, instructors, and other range personnel.
ABSTRACT
In acoustic intensity estimation, adding a microphone at the probe center removes errors associated with pressure averaging. Analytical bias errors are presented for a one-dimensional, three-microphone probe for active intensity, reactive intensity, and specific acoustic impedance in a monopole field. Traditional estimation is compared with the Phase and Amplitude Gradient Estimator (PAGE) method; the PAGE method shows an increased bandwidth for all three quantities. The two- and three-microphone methods are compared experimentally, showing reduced bias errors with three-microphone PAGE for active and reactive intensity, whereas using two microphones is preferred for specific acoustic impedance.
