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The Airborne ASW Platform as an Underwater Sound Source


OBJECTIVE: Develop a system utilizing the P-3, P-8, and MH-60 air platforms or a specially designed Deployable Airborne Source (DAS) or Unmanned Air Vehicle (UAV) as sound sources to augment the capability of existing airborne ASW systems for the detection of submarines. DESCRIPTION: It has been known for some time that the Navy"s P-3 Orion ASW aircraft can transmit sound into oceans and be detected (reference 1). The use of helicopters as a source of low frequency sound for the measurement of bottom characteristics has been proposed in references 2, 3 and 4. Additional articles (reference 5) show that it is possible to determine aircraft parameters from the signals projected into the sea. Current methods used in airborne ASW use A-size sonobuoys (4-7/8"x 36"cylinders) to provide active sound sources which generally operate at 1000Hz or higher. An aircraft source can easily provide frequencies below 100Hz and also in the infrasonic region (<20Hz). A sonobuoy source could not provide this capability in any reasonable size package. Since the patrol aircraft are already on station, they can be used as sources of opportunity and be utilized to augment existing airborne ASW systems. Using the typical frequency spectra of the P-3, P-8, MH-60 aircraft performance predictions can be generated. UAV or DAS vehicles can be designed as an airborne underwater sound source to generate an optimum frequency of transmission and source level. Determine the detection performance for both deep and shallow water environments utilizing the above aircraft. Characterize performance as a function of platforms (P-3, P-8, MH60, DAS and UAV), aircraft speed, altitude and flight pattern, sea state, wind speed and operating frequency. Define optimum processing for the time varying aircraft signature for both narrowband and broadband signals. These tasks will require the development of numerous software packages required for range prediction, field performance predictions, signal processing algorithm and software for processing the received echo. Additional tasks will include sea test planning, sea test coordination and analysis of data collected. PHASE I: Determine the feasibility of an in-air source as a method of generating underwater sound for submarine detection. Develop a complete propagation model for air to water and in-water propagation, and model the field detection performance. Determine the minimum aircraft source level needed and the maximum realizable aircraft source level. Determine the top level specification for a DAS or UAV which is specifically designed as an airborne source. Perform simulations as required using aircraft noise models or aircraft noise data. PHASE II: Extend and refine critical concepts and develop a prototype based upon findings in Phase I. Perform at sea tests with an airborne source (most like a UAV) to validate models, concepts and processing. Verify processing algorithms. PHASE III: Perform field level system sea tests. Transition system to the fleet and end users. Private Sector Commercial Potential/Dual-Use Applications: Methods and concepts developed under this task could provide underwater acousticians with a fast economical way to measure the ocean bottom parameters over a large area. Additionally, the UAV or DAS developed could be utilized as a source for remote sensing of the mineral content of the ocean, e.g. oil, gas by energy exploration companies.
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