A summary of the lateral cutoff analysis and results from NASA’s Farfield Investigation of No-boom Thresholds

Abstract

a larry.j.cliatt@nasa.gov b michael.a.hill-1@nasa.gov c edward.a.haering@nasa.gov d sarah.arnac@nasa.gov Abstract. In support of the ongoing effort by the National Aeronautics and Space Administration (NASA) to bring supersonic commercial travel to the public, NASA, in partnership with other industry organizations, conducted a flight research experiment to analyze acoustic propagation at the lateral edge of the sonic boom carpet. The name of the effort was the Farfield Investigation of No-boom Thresholds (FaINT). The research from FaINT determined an appropriate metric for sonic boom waveforms in the transition and shadow zones called Perceived Sound Exposure Level, established a value of 65 dB as a limit for the acoustic lateral extent of a sonic boom's noise region, analyzed change in sonic boom levels near lateral cutoff, and compared between real sonic boom measurements and numerical predictions.FIGURE 1. Lateral cutoff and transition region. 1

Sonic Boom Carpet Computation as a Basis for Supersonic Flight Routing

“…In real flight experiments producing actual sonic booms and measuring their strength and extent on the ground (the FaINT project [18]), Cliatt, Haering, Arnac, and Hill dealt with the problem of defining the exact boundary ("lateral cutoff") of sonic boom carpets. They found that evanescent waves right beyond that cutoff position, being perceived as a rumble and decaying exponentially in their course, can still be well discerned from ambient noise within a few miles' distance and can reach considerable loudness.…”

“…The presented methodologies have to be validated with the help of actual flight tests. Looking back at NASA's FaINT project [18,20], this seems to be a challenging task. Atmospheric conditions have to be predicted as accurately as possible, considering the actual duration of the flight, and the effect of unpredictable turbulence has to be quantified statistically.…”

Mach Cutoff Analysis and Results from NASA's Farfield Investigation of No-boom Thresholds

“…Metrics commonly accepted by the sonic boom community, such as Stevens' Mark VII 7 Perceived Level (PL70) American Institute of Aeronautics and Astronautics and A-weighted Sound Exposure Level (ASEL) were found to be less applicable for the waveform shape of the evanescent waves in the shadow zone. 8…”

Finding the boom: Phased array processing applied to sonic boom direction of arrival estimation

“…The purpose of the Farfield Investigation of No-boom Thresholds (FaINT) test was to investigate lateral and Mach cutoff conditions. 1,2 Lateral cutoff is the ground point where the sonic boom ray is refracted upward and thus no shock wave is observed past that point, although evanescent waves may be detected. 3 Lateral cutoff is demonstrated in Figure 1.…”

“…The overall goal of the FaINT test was to acquire data to aid in understanding the unique acoustic properties of audible edges, or transition zones, of the sonic boom carpet. 1 The goal of the acoustic phased array system was to collect data that could be used as a proof-of-concept demonstration of acoustic beamforming technology to determine the sonic boom direction of arrival.…”