Ultra Low Frequency (ULF) Sonobuoy

In order to counter the quiet modern submarine threat, sensor systems require innovative concepts and sensor developments that exploit the acoustic environment. There is a low acoustic ambient noise window the Ultra Low Frequency (ULF) band, in the 0.01 Hz to 0.1 Hz range, which has not been adequately explored with regard to tactical underwater acoustics. This acoustic band is attractive for passive detection, since propagation is good at these frequencies and target signals would be impossible to mask or suppress in the low ocean ambient noise in this band. This effort is to develop an air-deployed in-water acoustic sensor capable of Ultra Low Frequency performance in the ocean environment. The feasibility of developing a ULF acoustic sensor on a suspension that isolates it from ocean wave-induced motion will be demonstrated. Laboratory models will be fabricated to measure the appropriate parameters to assess ULF performance in the ocean. A means to discriminate self-noise from ambient noise will also be devised. The results from the Phase I effort will be used to develop and demonstrate an A-size over-the-side model in Phase II to show that the sensor meets performance requirements and measures acoustic ambient noise rather than sensor self-noise.