Sonic Boom Environment Under a Supersonic Military Operating Area

Abstract

A measurement program was conducted to record the sonic boom environment under a busy supersonic air combat maneuver training (ACM) arena. Simultaneous with sonic boom measurements, a complete record was made of supersonic activity. The measurements provided validation of the predicted elliptical pattern of C-weighted day-night average sound level (Lcdn) contours and demonstration of the nature of ACM sonic boom, which often includes non-W-wave signatures. Correlation of measured booms with flight activity data provided a quantitative model for prediction of LCdn contours for other similar airspaces. I. Introduction E NVIRONMENTAL assessment of sonic booms generated by supersonic air combat maneuver (ACM) training requires prediction of the C-weighted day-night average sound level (Lcdn). Initial efforts to compute LCdn contours1 were based on analysis of tracking data from an air combat maneuver instrumentation (ACMI) system, combined with simplified calculations2 of carpet booms (i.e., booms from steady level flight) for average supersonic conditions. The resultant model showed that supersonic activity occurs in an elliptical maneuver area centered between setup points used by pilots before engagement, and that LCdn contours are elliptical and aligned with the maneuver ellipse. Field validation of predictions for a new supersonic military operating area (MOA) confirmed the elliptical pattern, but measured LCdn values were at least 10 dB below predictions.3 The difference was thought to be due to the difference between carpet sonic boom footprints and the more complex footprints (described in Sec. III.B, below) which actually result from the supersonic phases of air combat maneuvers. The data collected and reported in Ref. 3 were, however, too sparse to draw general conclusions. Accordingly, a project was undertaken to measure sonic booms in a busy supersonic airspace. A 6 month sonic boom measurement program was conducted in the Lava/Mesa airspace at the White Sands Missile Range, New Mexico. This airspace is used for ACM training, primarily by F-15 aircraft from Holloman AFB. Thirty five sonic boom monitors were deployed. During the measurement period, all flight activity data for the airspace was reviewed and correlated with measured booms. A sample of ACMI tracking data was obtained for detailed analysis of particular events and to develop an understanding of how and when supersonic events occurred. Section II contains a description of the measurement program. Following completion of the measurements, statistical analyses were made of sonic booms identified with ACM activity.