Joint warfighting capabilities in the areas of Information Superiority, Combat Identification, Joint Readiness and Logistics, and Joint Countermine are particularly dependent on acoustic, magnetic, and seismic sensor technology. These sensors provide reliable undersea and terrestrial surveillance against threat targets. Such surveillance is required to achieve and maintain battlespace dominance to enable timely execution of joint/combined operations in support of national security objectives. Undersea acoustic sensor efforts are unique and critical to the Navy.
This subarea develops surveillance and environmental science using acoustics and magnetics to detect, classify, track, and localize quiet threat targets in all operating environments, across all missions, and with all platforms. Acoustic sensors are the primary sensors of choice to detect threat submarines operating below periscope depth. However, the increasingly quieter nuclear threat and the diesel-on-battery threat limit traditional passive narrowband processing, yielding shorter detection ranges. This demands higher array gain (by using more sensors) and adaptive signal processing to counter these quieting trends. Emphasis on active sonars is also increasing to counter this threat. The operational shift to the littorals presents a more difficult environment. The littoral region exhibits increased clutter from biologics, commercial shipping, and background ambient noise. This results in higher false alarm rates and greater weapons expenditures. To counter the environmental effects, fusion of data from acoustic and magnetic sensors with other nonacoustic sensors is finding increased emphasis. Effective multisensor data fusion offers more robust detection and classification performance and a greater range of adaptability. Larger array apertures require emphasis on affordability if such systems are ever to be fielded.
Navy applications include undersea surveillance in both open ocean and in highly variable, cluttered, shallow water areas. The sensors may be hull-mounted, towed, and deployed on a variety of platforms, including surface ships, submarines, fixed-wing aircraft, and helicopters. Army applications encompass shore area and battlefield surveillance used to detect and classify ground and air targets. The systems used are mounted on both stationary and mobile platforms. They are also used to detect mines at short ranges.
3.3.2.1 Goals and Timeframes. The worldwide proliferation of modern, quiet, diesel-electric submarines requires increased emphasis on the use of active sonar and full-spectrum passive processing. Improved classification for existing active sonar systems is the short-term (<5 years) goal. Within 10 years, high-gain passive systems and active sonar systems that can adapt to the highly variable littoral environment and accurately classify targets in high-clutter environments with reduced false alarm rates are required. Modern Army battlefield acoustic systems have demonstrated the capability to detect, classify, and identify ground targets at ranges in excess of 1 km and helicopters beyond 5 km with meter-sized sensor arrays, while netted arrays of sensors have been used to track and locate battalion-sized armor movements over tens of square kilometers in non-line-of-sight conditions.
Far-term improvements will extend these capabilities to tactical ranges. Significant goals are shown in Table VII-4. Advances for meeting these goals depend on progress in EO technology (3.7), understanding the ocean battlespace environments (3.12), and acoustic and magnetic materials.
| Fiscal Year | Goal |
|---|---|
| FY98 | Demonstrate optical array technology providing 5x decrease in acquisition costs with higher
bandwidths and dynamic ranges. Transition signal processing algorithms to the surface ship SQQ-89 sonar system, improving active classification by decreasing false alarms by an order of magnitude. Test 100x wider frequency band magnetic sensors. |
| FY99 | Transition signal processing algorithms to the helicopter dipping sonar system, improving active classification in shallow water. Demonstrate multistatic ASW operation using a battery-powered deployed active source with submarine towed array receivers and multistatic signal processing techniques. Demonstrate ability to track large vehicle formations with real-time tracking and identification. |
| FY00 | Demonstrate 5x increase in active source bandwidth. Test environmentally adaptable volumetric passive arrays that can provide near real-time aperture flexibility. |
| FY01 | Test the LBVDS. |
| FY05 | Demonstrate optical array technology providing a further 2x reduction (overall 10x relative to FY95) in towed array acquisition costs and programmable apertures. Demonstrate data-linked, autonomous-distributed, deployed sensor systems. Demonstrate 10x area coverage using integrated all-sensor fusing. |
System development to achieve the above goals requires a balanced investment in both signal processing and sensor designs. Improved sensor systems providing increased array gain, aperture, sensitivity, source level, and bandwidth will not be fully optimized without corresponding improvements in signal processing techniques. Accordingly, many projects in this subarea emphasize both sensor and signal processing technology development.
3.3.2.2 Major Technical Challenges. In general, the major technical challenges are to provide:
3.3.2.3 Related Federal and Private Sector Efforts. COTS plays a significant and growing role in this subarea. Telecommunication technology, fiber optics with associated laser, coupler, and splitter technology, polyvinylidene fluoride (PVDF) materials, and computationally intensive hardware are applicable examples.
The investment strategy for acoustic sensors is focused in two technology areas.
Sensor Signal Processing Technology. Efforts are aimed at developing active waveform designs, improving signal processing and displays to reduce clutter and false alarm rates encountered in cluttered environments, investigating bistatic and multistatic detection schemes, providing algorithms and data fusion techniques that increase Pd with reduced false alarms, and demonstrating long-range ground and air target detection and identification at low cost. Resolving closely spaced targets or target-like objects is addressed by improving array bearing accuracy and beamforming. Other techniques include passive processing, which exploits the complete spectrum of target-emitted signals, platform noise suppression, and ambient (e.g., wind) noise discrimination.
Sensor signal processing technology is divided into three major thrusts:
Active/passive sensor technology is divided into three major thrusts: acoustic/seismic transduction includes technologies for development of individual sensors or sources for both active and passive acoustics and passive seismic applications. Magnetic/nonacoustic sensors include technologies for development of individual sensors for magnetic and other nonacoustic applications, such as wake detection sensors. System development, integration, and test include efforts that incorporate the individual sensor developments from the previous two thrusts and develops platform-specific sensor systems for the detection/classification/localization of targets. This subarea includes testing in the operational environment for data collection, system testing, and concept demonstration, with the goal of gaining support for transition of such technologies to higher funding category programs.
3.3.3.1 Technology Demonstrations.
Lightweight, Broadband, Variable-Depth Sonar (DTO SE.13.02). The LBVDS will combine advances in high-energy density transduction materials and in broad frequency bandwidth waveform generation and signal processing in a 1- to 6-kHz sonar system that provides a shallow-water-environment USW capability to naval surface ship platforms. Real-time clutter rejection, reverberation suppression, target highlighting, and classification will be evaluated through sea tests of the broadband waveforms. A compact, towable source projector and receive array with manageable ship design and operational impact will be developed and used as the testbed. The LBVDS payoff will be an estimated 20-dB improvement in detection and classification, more rapid localization, and a false alarm goal of less than one per hour against quiet, slow submarines and mines in shallow water. The technology is targeted for transition to SC-21.
Multistatic Active ASW (DTO SE.14.02). This DTO develops and demonstrates a multi-static ASW capability, which incorporates an advanced acoustic source for use of surface ships, submarines, aircraft, and deployed distributed sensors. The majority of the DTO addresses the long-endurance, low-frequency active source (LELFAS) that starts in FY98 and will develop and demonstrate a leave-behind active source with a 30-day life that is commandable using underwater acoustic communications technology. The LELFAS will be packaged in a half-length MK 48 torpedo-sized unit, capable of deployment from a submarine, surface ship, or maritime patrol aircraft. The LELFAS source frequencies will be designed to be compatible with existing sensors in order to provide a multistatic ASW capability.
Affordable High-Performance Towed Arrays (DTO SE.15.01). This DTO develops, delivers, and operationally tests an improved towed array for tactical submarines and surface ships. The affordable array technology ATD is an integral portion of this DTO and is scheduled to start in FY98. This ATD will demonstrate a new approach for constructing all-optical towed arrays with potential for greater than 90% reduction in per-channel cost and inherent versatility for use over a very wide acoustic bandwidth.
Rapid Force Projection Initiative ACTD (JWSTP Precision Force DTO B.02). This ACTD is supported by hunter and standoff killer systems. Acoustics efforts that support the ACTD include the Hunter Sensor Suite (HSS) ATD (JWSTP Precision Force DTO B.09), the Integrated Acoustics System (IAS), the Intelligent Minefield (IMF) ATD, and the Remote Sentry (RS) ATD. The acoustic sensors and processing developed in these ATDs are used to provide early warning and target position to cue imaging sensors to detect targets.
3.3.3.2 Technology Development. System development to achieve the goals outlined in Section 3.3.3.1 requires a balanced investment in both signal processing and sensor designs. Improved sensor systems providing increased array gain, aperture, sensitivity, source level, and bandwidth will not be fully optimized without corresponding improvements in signal processing techniques. Accordingly, many projects in this subarea emphasize both sensor and signal processing technology development as stated in Section 3.3.3.
3.3.3.3 Basic Research. This subarea is interdisciplinary, drawing on efforts in materials, mathematical, computer, information, cognitive, neural, surveillance, and battlespace environmental sciences. Environmental effects play a major role in sensor performance, and insight into the complexities offers a means to develop adaptable systems.
