Jazmin Myres, Brigham Young University
Physical Sciences
In scan-based array measurements, stationary reference sensors are needed to temporally correlate the different measurement scans and produce coherent complex pressure fields. Because the number of references required increases with the number of subsources contributing to the sound field, an extended, partially correlated source comprising many ill-defined sources can result in significantly increased measurement complexity. A different approach to creating spatiotemporally coherent pressures is demonstrated here. Scan based measurements of a partially coherent line source have been taken in an anechoic chamber. This experimental data has been used to explore “stitching” together a complex pressure field by spatially overlapping measurement scans instead of using separate reference channels. Various methods of stitching have been explored and the most robust method identified. Unwrapping of intrascan phases is first accomplished with a two-dimensional phase unwrapping algorithm. Individual scan positions are then stitched together using median phase differences between multiple adjacent scans to create coherent planes of data. Amplitude-stitching is done by averaging across scans and preserving the integrated squared pressure across the overall aperture. This method has been verified using reference microphones. This stitching method has been applied to scan based measurements of a military aircraft, exhibiting its effectiveness dealing with a partially correlated complicated source. This method works well for low-frequency jet data, where there is not a ground-based interference null creating a physical phase discontinuity. This technique provides direction for efficient experimental design for scan-based array measurements of extended sources. [Work sponsored by ONR.]