You are here

Physics-Based Improvements for Continuous Active Sonar (CAS)


TECHNOLOGY AREA(S): Sensors, Electronics, Battlespace 

OBJECTIVE: Develop physics-based signal and automated information processing algorithms for Continuous Active Sonar (CAS) to improve Detection, Classification, and Localization (DCL). 

DESCRIPTION: Navy Cruisers and Destroyers engage in anti-submarine warfare (ASW) using a variety of methods to perform DCL of submerged threats. CAS uses swept linear frequency-modulated signals transmitted at 100% duty cycle to detect, classify, and localize submarines. CAS offers the benefit of improved detection and continuous tracking relative to traditional pulsed active sonar. In some ways, CAS is similar to Frequency Modulated Continuous Wave (FMCW) radar and may benefit from techniques developed in the radar community. Expert analysis of the CAS method suggests that there may be areas where CAS DCL can be improved. CAS has some physics-based limitations, which cause degraded performance. Variation in transmitter speed through the water causes what is known as Doppler effect or shift. Doppler shift changes the frequency of the transmitted waveform such that the received waveform frequency is different from the transmitted waveform frequency, which is known as signal-mismatch. Signal-mismatch will cause false alarms. Changes in the target heading, bearing, and speed can cause Doppler shift in the signal. Multiple Doppler banks in the detector partially recover signal-gain losses, but these introduce signal-mismatch adding to degraded DCL performance. Because of the way CAS signals are processed, these unquantified Doppler shifts can cause range uncertainty. Range uncertainty is frequency-dependent, causing time-varying alterations and breaks in tracks. These factors limit the effective range of coherent update rates, complicate downstream processing, and make it difficult for operators’ easy assessment of displayed data. Research of current commercial sonar developments show that they utilize various forms of active acoustic transmission and reception but do not use continuous active sonar. Innovative physics-based automated DCL algorithms should reduce range uncertainty by 50%, reduce signal-mismatch by 3dB, reduce false alarms by 25%, and improve tracking. These algorithms may be in the class of front-end linear signal processing and detection methods, back-end improvements to classification, clustering and tracking, or methods that rely on multiple methods used in concert. These improvements would significantly increase CAS capability without requiring expensive hardware changes. Additionally, these improvements would enable streamlined processes to reduce operator workload and staffing. The Phase II effort will likely require secure access, and NAVSEA will process the DD254 to support the contractor for personnel and facility certification for secure access. The Phase I effort will not require access to classified information. If need be, data of the same level of complexity as secured data will be provided to support Phase I work. 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 Security Service (DSS). The selected contractor and/or subcontractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances, in order to perform on advanced phases of this contract as set forth by DSS and NAVSEA 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 advance phases of this contract. 

PHASE I: Develop an innovative concept for physics-based signal and automated information processing algorithms that meet the requirements in the description. The concept will show it can be feasibly developed into a useful product for the Navy. Feasibility will be established through analytical modeling and development with simulated or recorded sea data. The Government will provide the data. The Phase I Option, if awarded, will include the initial design specifications and capabilities description to build a prototype in Phase II. Develop a Phase II plan. 

PHASE II: Based on the results of Phase I modeling and the Phase II Statement of Work (SOW), design, develop, and deliver a prototype physics-based signal and information processing algorithm for CAS performance improvement. The prototype will demonstrate system performance through the required range of parameters given in the description, including testing with diverse data sets. Data sets from Cruise/Destroyer Hull Sonar and/or Littoral Combat Ship Variable Depth Sonar (LCS-VDS) employing continuous waveforms will be used to validate the prototype’s capabilities. The Government will provide the data. The demonstration will take place at a Government- or company-provided facility. Prepare a Phase III development plan to transition the technology for Navy production and potential commercial use. It is probable that the work under this effort will be classified under Phase II (see Description section for details). 

PHASE III: Assist the Government in transitioning the technology for Navy use in an operationally relevant environment to allow for further experimentation and refinement. The prototype will be integrated into the IWS 5.0 surface ship ASW combat system Advanced Capability Build (ACB) program used to update the AN/SQQ-89 Program of Record. Commercial applications that currently utilize various forms of active acoustic transmission and reception that could benefit from a continuous active sonar approach include oil exploration; seismic survey; rescue and salvage; and bathymetric survey. 


1: van Vossen, Dr. Robbert. "Anti-Submarine Warfare with Continuously Active Sonar." Sea Technology, November 2011.

2:  McDermott, Jennifer. "New sonar designed to close technology gap." The Day, 29 July 2010.

3:  D’Amico, Angela and Pittenger, Richard. "A Brief History of Active Sonar." Aquatic Mammals, 2009,

4:  Wolff, Christian. "Frequency-Modulated Continuous-Wave Radar (FMCW Radar)." Radar Tutorial, December 2009.

KEYWORDS: Continuous Active Sonar; Antisubmarine Warfare; Active Sonar Waveforms; Active Sonar Detection; Active Sonar Tracking; Active Sonar Clutter Reduction 


Meg Stout 

(202) 781-4233 

Christian Hempel 

(401) 832-8648 

US Flag An Official Website of the United States Government