Abstract by Reese Rasband
Physics and Astronomy
Employing digital pole-shifting filters to improve low-frequency response of sonic boom measurements
High-fidelity measurement of sonic boom waveforms requires microphones and data acquisition hardware with frequency responses that extend well below 1 Hz. When hardware do not meet these requirements, however, digital pole-shifting filters that account for limitations of conventional hardware can be used in post-processing to increase the low frequency recording quality. This approach is demonstrated for sonic boom recordings from the NASA Quiet Supersonic Flights 2018 (QSF18) measurement campaign. Recordings of several booms at multiple measurement sites using different data acquisition hardware and microphone combinations were used to understand the robustness of the processing technique. In particular, manufacturers report nominal hardware roll-off frequencies with which filters can be designed. However, the QSF18 data can be used to derive filters computationally using a mean-square error method. Results, including residual errors and other limitations, are discussed. The transferability of the technique is further described through application to a launch vehicle reentry sonic boom, a markedly different sonic boom recording.