Battlespace Simulations (United States)

Many auditory detection tasks employ discrete stimulus samples, presented during well-defined, brief observation intervals at predictable times. However, real-world listening is a continuous process without clearly defined intervals possessing indicators of when to listen and respond. The current study was designed to investigate the differences between a discrete, interval-based method and a continuous, free-response method. Increasing understanding of differences in methodology leads to a model predicting real-world perception from interval-based laboratory detection data. Real and simulated aircraft over-flight signals were presented to human subjects in a continuous, free-response task in which the subjects indicated when they could detect the signal. The same signals were also divided into 1-s audio files, which were presented to the same subjects in different sequences using a single-interval, forced-choice paradigm. The results indicated that the presentation sequence does not have an effect on human performance. Comparison of psychometric function derived from interval-based and free-response data indicated a shift to higher signal-to-noise ratios on approach when no clear response interval is provided, but the same shift was not observed on departure.

Near-field acoustical holography has been used previously to study characteristics of jet noise radiated from tactical aircraft. This paper investigates frequency-dependent source and radiation characteristics of an installed GE F404 engine at afterburner, as determined using multisource statistically optimized near-field acoustical holography. Included in the analyses are the number of partial fields required to represent the source, the extent of the region of maximum sound power production, and directional characteristics. Comparisons are made with other source reconstructions of high-performance engines. [Work supported by ONR.]

Noise from a tactical aircraft can impact operations due to concerns regarding military personnel noise exposure and community annoyance and disturbance. The efficacy of mission planning can increase when the distinct, complex acoustic source mechanisms creating the noise are better understood. For each type of noise, equivalent acoustic source distributions are obtained from a tied-down F-35B operating at various engine conditions using the hybrid method for acoustic source imaging of Padois, Gauthier, and Berry [J. Sound Vib. 333, 6858-6868 (2014)]. The source distributions for the distinct noise types are obtained using different sections of a 71 element, ground-based linear array. Using a subarray close to the nozzle exit plane, source distributions are obtained for fine-scale turbulent mixing noise and broadband shock-associated noise, although grating lobes complicate interpretations at higher frequencies. Results for a subarray spanning the maximum sound region show that the multiple frequency peaks in tactical aircraft noise appear to originate from overlapping source regions. The observation of overlapping spatial extent of competing noise sources is supported by the coherence properties of the source distributions for the different subarrays.

Multisource statistically optimized near-field acoustical holography (M-SONAH) improves the field reconstruction process by directly incorporating into the pressure propagator types of wavefunctions that correspond most closely to the source geometries of interest. The M-SONAH method has previously been used to localize acoustic sources in a full-scale jet engine plume above a rigid reflecting plane by adding a second set of cylindrical wavefunctions corresponding to the image source. Here, M-SONAH theory is extended to obtain the vector particle velocity and, by extension, the acoustic intensity. Discussed are two examples that relate to the full-scale jet noise-with-image-plane reconstruction problem: (1) a Gaussian line source with image and (2) a jet-like wavepacket and image, with hologram geometry identical to that of the full-scale experiment. The results from both examples reveal intensity errors less than 3 dB and 10 degrees within the top 20 dB of the reconstruction region. The results also suggest that intensity reconstruction magnitudes less than those obtained at the measurement aperture edges should be discarded.

Construction of the equivalent acoustic source model for high-performance military aircraft noise presented in this paper begins with a decomposition of sound levels, from ground-based microphones 11.7 m from a high-performance military aircraft, into portions matching the similarity spectra associated with large-scale and fine-scale turbulent mixing noise (LSS and FSS). [Tam et al. AIAA Paper 96-1716 (1996)]. A Fourier transform of the spatial distribution of the decomposed levels yields frequency-dependent wavenumber spectra [Morris, Int. J. Aeroacoust. 8, 301-316 (2009)]. Each LSS-educed wavenumber spectrum corresponds to a wavepacket, consisting of a spatially varying amplitude distribution with a constant axial phase relationship. This wavepacket model produces a directional, coherent sound field. However, the asymmetry in the LSS-educed wavenumber spectra may indicate that a nonuniform phase relationship is a more physical choice that could be correlated to the axial variation in convective speed. The FSS component is modeled with a line of incoherent monopoles whose amplitude distribution is related to the FSS-educed wavenumber spectrum. While this level-based model is limited, the addition of the FSS-related source yields a better match to the noise environment of a high-performance military aircraft than is found using a single coherent wavepacket. [Work supported by ONR.]

The newly revised sunspot number series allows for placing historical geoeffective storms in the context of several hundred years of solar activity. Using statistical analyses of the Geostationary Operational Environmental Satellites (GOES) X-ray observations from the past ~30 years and the Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO) Coronal Mass Ejection (CME) catalog (1996-present), we present sunspot-number-dependent flare and CME rates. In particular, we present X-ray flare rates as a function of sunspot number for the past three cycles. We also show that the 1-8 AA X-ray background flux is strongly correlated with sunspot number across solar cycles. Similarly, we show that the CME properties (e.g., proxies related to the CME linear speed and width) are also correlated with sunspot number for SC 23 and 24. These updated rates will enable future predictions for geoeffective events and place historical storms in the context of present solar activity.

Mixing noise from a jet engine originates from an extended spatial region downstream of the nozzle and is partially correlated both spatially and temporally. Previously, the coherence properties in the downstream direction of the sound field of a tethered military aircraft were investigated, resulting in the identification of different spatial regions based on coherence length [B. M. Harker et al., AIAA J. 54, 1551-1566 (2016)]. In this study, a vertical array of microphones to the side of the jet plume is used to obtain the azimuthal coherence of the sound field. Although multipath interference effects and a limited angular aperture make coherence length calculation impossible, information about upper and lower bounds can be extracted. The measured azimuthal coherence as a function of downstream distance and frequency is then compared to that predicted by sound field reconstructions using multisource, statistically-optimized near-field acoustical holography (M-SONAH) [A. T. Wall et al., J. Acoust. Soc. Am., 139, 1938-1950 (2016)]. This comparison helps to benchmark the performance of a reduced-order M-SONAH algorithm that employs only axisymmetric cylindrical basis functions to represent the sound field.

Simpson et al. [Proceedings of Meetings on Acoustics 19, 050140 (2013)] measured localization accuracy for sequences of noise bursts masked by simultaneous sequences of noise burst maskers (1 or 2). Targets were distinguishable from the maskers only in that all bursts within a target sequence arose from the same location, whereas each burst in a masker sequence arose from a different, randomly selected location. In this task, the spatial information extracted from each burst both helps define which element is the target (“target identification”) and where that target is located (“target localization”). Presumably, the listener is more focused on target identification early in the sequence and on target localization later in the sequence. And so, it is not surprising that localization accuracy increases dramatically as the length of the sequences is increased. This talk will compare these results to the foundational work of Hafter and his colleagues [e.g., Hafter, 1997, in Binaural and Spatial Hearing in R...

A sequence of nine weather balloons were launched recently over the island of Hawaii during the nights of 12, 13, and 17 December, 2002, providing measurements of ascent rate, horizontal wind speed and direction, temperature, and other quantities. The measurements show short intervals of altitude with a large increase in ascent rate, occurring only near the tropopause, indicating regions of strong upward air velocity at this location. The large ascent rates correlate well to the strength of a jet stream, and with the presence of a local critical level, indicating mountain waves as the primary cause. No corresponding decreases in ascent rate were measured, suggesting strong three‐dimensional effects.