N121-088 TITLE: Compact Airborne Acoustic Device (CAAD)

TECHNOLOGY AREAS: Sensors, Battlespace, Weapons

ACQUISITION PROGRAM: PMS-495: COBRA Block III; ONR: FNC SHD-06-03

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted". The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: Develop and demonstrate an innovative compact airborne acoustic source that can be flown on the Fire Scout Vertical Takeoff and Landing Tactical Unmanned Aerial Vehicle (VTUAV) for use as an insonification device.

DESCRIPTION: Buried objects can be detected by systems that combine an acoustic source to excite the ground and a laser-based electro optic imaging technique. In order to develop an airborne detection capability a flyable acoustic source is required. The acoustic source must provide adequate energy on the ground from significant altitudes. Preliminary tests show that a sound pressure level above 100 dB is required on the ground. This acoustic energy on the ground must be in the low frequency regime as shown in references. There is interest in deploying the compact acoustic source from an unmanned airborne vehicle (UAV). The acoustic source and the laser-based electro optic imaging system together will be integrated onto this platform so size and weight are of prime importance. Buried objects can be detected by systems that combine an acoustic source to excite the ground and a laser-based electro-optic imaging technique. In order to develop an airborne detection capability, a flyable acoustic source that provides adequate energy on the ground from significant altitudes is required. Preliminary tests show that a sound pressure level above 100 dB is required on the ground. This acoustic energy on the ground must be in the low-frequency regime as shown in the references. There is interest in deploying the compact acoustic source from an unmanned airborne vehicle. The acoustic source and the laser-based electro-optic imaging system will be combined and integrated onto this platform. Size and weight are of prime importance; therefore, the acoustic source must be compact and provide adequate acoustic energy on the ground in the correct frequency bands.

Currently available acoustic sources don't achieve the energy levels needed to excite the ground at the desired altitudes and are not compact when operating in the low frequency regime. Even very loud hailing devices are limited in total output and in the region over which they operate. Insonification of buried objects to generate motion requires a significant energy level which must be provided in certain optimal frequency bands.

Innovative approaches are sought to develop an acoustic source capable of achieving sound pressure levels (SPLs) approaching 170 dB plus equivalency (as referenced to 20 micro Pascal at 1 meter) in order to provide adequate SPLs at ground-level when flying at altitudes up to 1000 feet. These SPL levels must be provided at various pure-tone frequencies, on the ground, in the low-frequency regime of 90 to 400 Hz. An analysis of alternatives will be done to trade device size, frequency range, output sound pressure level, output waveform, and operational repetition rate. Innovative approaches that can overcome inverse square law losses such as creating near-field effects that mitigate these losses in order to help with long-range output should be considered. Other innovative approaches such as air cannons should also be considered. Trade-off should be considered for the acoustic device output delivery modes to include: individual narrow-band frequencies delivered as continuous and repeatable single frequency tones, multiple frequencies delivered as continuous and simultaneous or as repeatable swept multi-frequency tones, broadband impulses, shock waves, etc. The device should be capable of a sustained operational rate on the order of 10-20 cycles per second to be compatible with typical laser-based electro- optic imaging systems. Higher repetition rates can be considered. An emphasis on compactness, weight, and power will be critical due to platform limitations. Approaches can include the use of electro-mechanical acoustical systems, combustion chambers, prop-fans, or other techniques as appropriate if they can be designed to achieve the desired output.

PHASE I: The contractor will design and develop a concept for a flyable compact acoustic source capable of achieving the performance requirements listed in the description. The contractor will validate the concept using performance modeling. In the Phase I option the contractor will include the initial layout and a description of the performance specifications of the source that will be fabricated in Phase II.

PHASE II: The contractor will fabricate, demonstrate, validate, and deliver the prototype acoustic source developed in Phase I.

PHASE III: Integration of the prototype acoustic source onto the demonstration platform with a laser-based electro-optic imaging system, flight test the complete system, and integrate into the Sea Shield FNC and/or the COBRA acquisition program.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The ability to enhance detection of buried objects would be extremely useful for humanitarian de-mining, IED detection, general buried object detection, detection of buried pipelines and cables, detection of buried items in natural disaster assessment, and advancement of hailing devices.

REFERENCES:
1. Steve Moran, et.al, Lite Cycles Incorporated (USA), Rapid overt airborne reconnaissance (ROAR) for mines and obstacles in very shallow water, surf zone, and beach; SPIE Proceedings 5089, 214 (2003).

2. J. M. Sabatier and N. Xiang, Laser-Doppler-based acoustic-to-seismic detection of buried mines; SPIE Proceedings 3710, 215 (1999).

3. J. M. Sabatier and N. Xiang, An investigation of a system that uses acoustic-to-seismic coupling to detect buried anti-tank landmines; IEEE Trans. Geoscience and Remote Sensing 39, 1146-1154 (2001).

4. J. M. Sabatier, H. E. Bass, L. N. Bolen and K. Attenborough, Acoustically induced seismic waves; J. Acoust. Soc. Am. 80 (4), 646-649 (1986).

5. D. M. Donskoy, Nonlinear vibro-acoustic technique for land mine detection; SPIE Proceedings 3392, 211-217 (1998).

6. D. M. Donskoy, A. Ekimov, N. Sedunov and M. Tsionskiy, Nonlinear seismo-acoustic land mine detection: Field test; J. Acoust. Soc. Am. 110, No. 5, Pt. 2, 4pPA2, 2757 (2001).

KEYWORDS: Acoustic Source, Insonification, Littoral MCM, Airborne Reconnaissance, Buried Mine Detection, IED Detection

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