Acoustic Tomography Using Tactical Sensors

Navy SBIR 21.2 - Topic N212-116
NAVAIR - Naval Air Systems Command
Opens: May 19, 2021 - Closes: June 17, 2021 (12:00pm edt)

N212-116 TITLE: Acoustic Tomography Using Tactical Sensors

RT&L FOCUS AREA(S): General Warfighting Requirements (GWR)

TECHNOLOGY AREA(S): Battlespace Environments

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Inform Air Anti-Submarine Warfare (ASW) operations by applying acoustic tomography through leveraging the tactical sonobuoy sensors used for wide-area search to estimate the three-dimensional sound-speed field.

DESCRIPTION: Air ASW systems rely on environmental information to plan sensor fields and assess the performance of the mission afterwards. In future Air ASW systems designs, environmental predictions will be used to better separate targets from clutter. Sound speed is a fundamental component of this suite of environmental information and is critical for determining transmission loss. Transmission loss is an important parameter in reconciling the sonar equation and is needed to understand achieved search performance and to derive performance estimates. Maximum acceptable Transmission Loss is highly dependent on environmental factors such as ambient noise and reverberation.

Currently, Maritime Patrol Reconnaissance Aircraft rely on a combination of pre-flight estimates of the sound-speed field, augmented with sparse direct measurements of the sound speed using air expendable bathythermograph (AXBT) sonobuoys. An AXBT provides the sound-speed profile only for the point at which it enters the water, however; distributed fields of sonobuoys can extend over large areas and more complete estimates of the sound-speed across the sonobuoy field are needed in order to provide improved mission planning and execution. Dropping more AXBT sensors is not desired because of payload constraints on the aircraft, lost search time deploying more sensors for environmental assessment, and increased cost for each mission from dropping more buoys.

Acoustic tomography has been previously applied to improve ASW situational awareness [Ref 1-3]. This SBIR topic will take advantage of the information already used by Air ASW systems to infer the sound-speed field by using acoustic tomography drawn from bistatic active sonar measurements used in wide-area search. Acoustic tomography [Ref 4] measures acoustic travel times between two points, along a multitude of paths, crossing at many different angles, to reconstruct the sound speed in a manner similar to medical computer aided tomography (CAT) scans. One constraint associated with using data from air deployed sensors is the limited bandwidth of both the source and receiver (on the order of 100 Hz). It may also be the case that not all receivers in the field reliably receive the source transmission. Any derived sound speed should be less than 1% different from a measured value at the same depth when a measured value is available for comparison.

Modern multistatic sonobuoy fields offer a similar multitude of paths, and aircraft avionics can readily measure travel times as part of the sonar processing chain. In recent years, the size of the sonobuoy fields have grown, and the accuracy of buoy location estimates during a mission has increased. These two trends appear to make acoustic tomography using tactical sensors more feasible than in the past.

Air ASW systems that benefit from this technology include: mission planning, tactical decision aides, post-mission assessment systems at tactical support centers, and onboard target detection processing systems.

Work produced in Phase II may become classified. Note: The prospective contractor(s) must be U.S. owned and operated with no foreign influence as defined by DoD 5220.22-M, National Industrial Security Program Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Counterintelligence and Security Agency (DCSA) formerly Defense Security Service (DSS). The selected contractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances. This will allow contractor personnel to perform on advanced phases of this project as set forth by DCSA and NAVAIR in order to gain access to classified information pertaining to the national defense of the United States and its allies; this will be an inherent requirement. The selected company will be required to safeguard classified material IAW DoD 5220.22-M during the advanced phases of this contract.

PHASE I: Conduct a study to account for the impact of various factors (e.g., buoy location uncertainty (0 – 1 NMI uncertainty), time of arrival uncertainty (+/- 1 sec or less), and sonobuoy spacing (5 km – 15 km), demonstrating the feasibility of the proposed approach through the use of simulations. Demonstrate using simulations that transmission loss estimates for tactical sensors, based on climatology and now-casts (Generalized Digital Environmental Model (GDEM) or Hybrid Coordinate Ocean Model (HYCOM)), can be improved by using acoustic tomography methods via tactical sensors. Demonstrate through simulations that Transmission Loss prediction accuracy using acoustic tomography for the entire multistatic sonobuoy field is within +/-6 dB of TL estimates generated by using GDEM or HYCOM at the point where that data is available. The Phase I effort will include prototype plans and software architecture to be developed under Phase II.

PHASE II: Develop a prototype processing algorithm suitable for integration into mission planning tools and onboard target discrimination algorithms. Analyze real-world data to show improved reconciliation of measured target detections and measured echo levels with environmental predictions of echo levels and signal excess that incorporate tomography results.

Work in Phase II may become classified. Please see note in Description paragraph.

PHASE III DUAL USE APPLICATIONS: Finalize and implement the capability as part of an operational sonar system. Transition of this capability should utilize the Advanced Product Builds (APB) process.

The tomography techniques developed under this effort have application across the Navy for sonar, radar, electro-optic, and other sensor devices. Other commercial applications for this technology are oil exploration and predicting storm tracks based on sea temperature.


  1. Cornuelle, B., Munk, W. and Worcester, P. "Ocean acoustic tomography from ships." Journal of Geophysical Research: Oceans, 94(C5), May 15, 1989, pp. 6232-6250.
  2. The Acoustic Mid-Ocean Dynamics Experiment Group. "Moving Ship Tomography in the North Atlantic.", EOS Science News, American Geophysical Union, 75(2), January 11, 1994, pp. 17-23.
  3. Munk, W., Worcester, P. and Wunsch, C. "Ocean acoustic tomography." Cambridge University Press, 2009.
  4. Delbalzo, D. and Klicka, J. "Uncertainty-based adaptive AXBT sampling with SPOTS." [Paper presentation]. OCEANS ’09, MTS/IEEE, Biloxi, MS, United States, October 26-29, 2009.
  5. "DoD 5220.22-M National Industrial Security Program Operating Manual (Incorporating Change 2, May 18, 2016)." Department of Defense, February 28, 2006.

KEYWORDS: Acoustic Tomography; Sound Speed Profile; Multistatics Mission Planning; Target Detection; Target Search; Intelligent Search; sonobuoy


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