Ultra Low Frequency (ULF) Sonobuoy

For the Phase I effort the target low end frequency was 0.02 Hz. This necessitated the need for a horizontal fiber optic slack line and Neutrally Buoyant Sensor Package with active buoyancy control to isolate the sensor from flow and sea state induced mechanical noise. For Phase II the low end frequency has been changed to 1.0 Hz. This is a significant change and allows the use of a passive multi-element isolation suspension system and flow shield to isolate the sensor from flow and sea state induced mechanical noise. This has several advantages including: lower development cost, lower production cost, and better accuracy on target location (with a horizontal slack line the sensor package drifts away from the surface unit complicating data processing). Lower cost will be realized across mechanical, electrical and acoustic systems. The change in low end frequency also opens up opportunities in acoustic sensor design and selection. Another change from Phase I to Phase II is the requirement for a 3 axis vector sensor and omni directional hydrophone to allow a down looking cardioid beam pattern.