Using ray tracing to predict far-field spectral time histories of Falcon 9 launch noise

Accurate far-field acoustic predictions of rocket noise are increasingly relevant due to the rise in launch cadence. Improved modeling is important for understanding how noise affects communities and wildlife. This study presents a ray-tracing method for predicting spectral time histories for the SARah-1 Falcon 9 launch from Vandenberg Space Force Base (VSFB), CA. Atmospheric profiles were constructed using radiosonde data from a weather balloon launched at VSFB on launch day, accessed via the NOAA IGRA database. An iterative ray-tracing approach calculated sound ray travel paths for different launches, measurement locations, and trajectories, to within 10 m. A frequency-dependent source directivity function was constructed by backpropagating measured acoustic data along the calculated ray paths. This function was then applied and forward-propagated along ray paths calculated for a SARah-1 measurement station, enabling prediction of a spectrogram a small time offset as the only tuning parameter. The predicted spectrogram closely matched measured SARah-1 data, with high correlation and reasonable mean bias. This approach has been applied to additional launches and stations to validate its general applicability.