Testing a spiral beamforming array for airborne acoustics

Airborne acoustic signature characterization of watercraft is one of the interests of Naval Surface Warfare Center Carderock Division (NSWCCD). A twenty-element planar spiral array was recently designed for this purpose. In June 2024, the system was used in a collaborative measurement campaign with East Carolina University in Wanchese, NC. The array was fixed to an offshore platform and recorded pure tone bursts of 250, 500, 1000, and 2000 Hz from a Long Range Acoustic Device (LRAD) positioned at ranges from 250 m up to 2 km. Within a 10 min period, estimations of transmission loss and SNR in upward refraction cases varied by 10–20 dB for each frequency. Using a MATLAB-based time delay beamformer, SNRs typically increased by up to 5–10 dB. Broadside and off-angle results are discussed.