In a recent study of noise from a T-7A-installed GE F404 engine, microphones along 38 and 76 m (125 and 250 ft) arcs were mounted 1.5 m (5 ft) above the ground to quantify human impact. While helpful for this purpose, the resulting multipath effects pose challenges for other acoustical analyses. For jet noise runup measurements, these effects are complicated by the fact that the noise source is extended and partially correlated and its spatial properties are frequency dependent. Furthermore, a finite-impedance ground surface and atmospheric turbulence affect interference nulls. This study applies a ground-reflection method developed previously [Gee et al., Proc. Mtgs. Acoust. 22, 040001 (2014)] for rocket noise measurements. The model accounts for finite ground impedance, atmospheric turbulence, and extended source models that are treated as coherent and incoherent arrays of monopoles. Application to the ground runup data to correct the 38 and 76 m spectra at a range of angles suggests the incoherent line source model is more appropriate at sideline angles whereas the coherent source model is more appropriate for upstream and downstream propagation. Comparisons with near-field data and similarity spectra show that, while imperfect, this method represents an advancement in correcting jet noise spectra for ground reflection effects. [Work supported by ONR Grant No. N00014-21-1-2069.]

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ANSI/ASA standard S12.75 (2012) provides guidance on allowable meteorological conditions for acoustical measurements of installed high-performance jet engines. This paper investigates meteorological effects on acoustic data acquisition by analyzing recent measurements of a T-7A-installed GE F404 engine. During this measurement, the aircraft was run up six times at engine powers from idle to full afterburner, with test conditions following those prescribed by S12.75. However, far-field spectra show variability between runs, despite relatively uniform test conditions. Measurements of the vertical temperature gradient show a correlation between the gradient and spectral characteristics. This analysis suggests that local temperature profiles must be considered more carefully in future full-scale measurements. [Work supported by ONR Grant No. N00014-21-1-2069.]

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