Inert Impulsive Expendable Acoustic Source (IIEAS)

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Sustainment OBJECTIVE: Develop an expendable impulsive underwater sound source without explosives or combustible gas packaged in A-size sonobuoy and/or Signal, Underwater Sound (SUS) form factor. DESCRIPTION: High-energy impulsive underwater acoustic sources such as air-guns, sparkers, or explosive/implosive charges are used for oil and gas exploration, seabed characterization, and underwater target detection. Explosive charges, such as the SUS source, are especially convenient for being compact and mobile for easy deployment by surface or airborne platforms. SUS is routinely used to conduct transmission loss experiments used to determine bottom loss parameters which are used in databases for seabed bottom properties. A typical SUS charge contains the chemical compound trinitrotoluene, TNT; a chemical compound used as an explosive material requiring special handling. However, it's been shown that impulsive sound sources, such as created by the implosion of lightbulbs, can be useful for transmission loss or seabed characterization experiments. This STTR topic seeks development of an impulsive sound source without explosives or combustible gas packaged in A-size sonobuoy and/or SUS form factor. PHASE I: Develop an impulsive underwater acoustic source concept that does not explosives or combustible gas. The source shall exhibit a Peak Source Level greater than or equal to 190 dB//1 Pa@1m at water depths of 10 200 m or deeper. Energy Spectral Density should be within +/- 10 dB re 1muPa^2 s/Hz @ 1 m from 30 Hz to greater than or equal to 20 kHz. The concept should describe the mechanistic underpinnings of the source and support it with models and simulations. Simulations should demonstrate the source level and spectral content for as a function of depth in a representative ocean environment. PHASE II: Develop, build, and demonstrate a hardware version of the source concept resulting from Phase I. The demonstration source does not have to be expendable, but should demonstrate the capabilities for source level and spectral characteristics stated in the requirements. Demonstrate that the impulsive source signature is repeatable and predictable for a given source depth. Develop a capability for triggering the source at a specific depth over the range specified. Develop a plan in consultation with the Navy for demonstrating the source to include compliance with environmental regulations. After demonstrations, develop a design for an expendable version of the source with form factors compatible with A-size sonobuoy and SUS. PHASE III DUAL USE APPLICATIONS: The expected transition will be an inert impulsive expendable underwater acoustic source that can be used for transmission loss surveys, geotechnical surveys, and other naval or civil applications. The inert nature of the source will make handling much safer than currently used sources. Phase III tasking shall include refining the prototype design and fabrication of a near-final product suitable for testing. Sufficient test articles should be manufactured to establish repeatability of the specified source characteristics. An at-sea experimental test and evaluation plan shall be developed and executed in consultation with the sponsor. Test articles meeting the SUS form factor can be demonstrated by being deployed by hand or with the use of a suitable launcher from the deck of a ship. Test articles meeting the A-size sonobuoy form factor must demonstrate compatibility with standard launch tubes with a test plan developed in consultation with the platform operator. In their final forms, the SUS form factor is expected to be used for operational surveys or in support of basic and applied research. The A-size sonobuoy form factor can be dropped from helicopters for ASW search and or environmental characterization. REFERENCES: Heard, Garry J.; McDonald, M.; Chapman, N.R. and Jashke, L. Underwater Light Bulb Implosions A useful acoustic source. Oceans '97. MTS/IEEE Conference Proceedings Page(s), Vol.2, 1997, pp. 755-762. DOI: 10.1109/OCEANS.1997 Chapman, N.R. Source levels of shallow explosive charges. J. Acoust. Soc. Am., 84(2),1988, pp. 697-702 DOI.org/10.1121/1.396849 McNeese, A.R.; Lee, K.M.;, Sagers, J.D.;, Lee, M.J. and Wilson, P.S. Experimental observations of a rupture induced underwater sound source. J. Acoust. Soc. Am. 148(4), 2020, pp. EL370 EL374. doi.org/10.1121/10.0002259 KEYWORDS: Underwater Acoustics; Sound Propagation; Sound Source; Geoacoustic Inversion; Bubble pulse; Implosion