Technology for the United States Navy and Marine Corps, 2000-2035: Becoming a 21st-Century Force Volume 7: Undersea Warfare (1997) / Chapter Skim
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1 Antisubmarine Warfare
1 Antisubmarine Warfare
Pages 7-42
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From page 7... ...
The United States has vital economic, political, and military interests and commitments around the globe. Recognizing this fact, the National Military Strategy1 states that naval forces ".
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From page 8... ...
Currently, ASW resources are relatively constrained by the overall pressure on military spending, competing warfare priorities, and a continuing debate over the relative significance of the submarine threat. The continuing drawdown in naval forces and current deemphasis on ASW have seriously eroded the Navy's capabilities in this warfare area at a time when potential future adversaries are rapidly acquiring advanced quieting techniques and other offensive submarine technologies.
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From page 9... ...
Russia has recently given additional emphasis to the importance of its Navy, particularly submarines, by creating a budget line for them that is separate from the rest of the armed forces. The People's Republic of China, which currently has a submarine force that is, for the most part, obsolete, is investing heavily in submarine technology, including designs for nuclear attack submarines, strategic ballistic missile submarines, and advanced conventional submarines expedited by the purchase of KILO-class submarines from Russia.
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From page 10... ...
It is a misconception that littoral waters are always shallow. Although it is true that shallow waters are always in littoral areas, an examination of the bathymetry of potential regional conflict areas reveals that the littoral regions encompass the full range of depths from deep to shallow.
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From page 11... ...
There are no quick fixes, however; a dedicated, focused research effort will be required to develop and effectively deploy these solutions. For example, advanced signal processing techniques must be coupled with a thorough understanding of target and environmental parameters and their variabilities.
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From page 12... ...
Signal processing algorithms based on coherent, range-dependent propagation codes using real-time environmental inputs now can exploit this coherence. · The reduction of wide-band threat signatures in the VLF band is difficult because it involves the entire platform, and hull coatings are less effective at damping these long-wavelength acoustic signals.
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From page 13... ...
The necessary components of an effective ASW technology development program are as follows: · Well-posed science and technology; · At-sea experiments with sensors that are both well calibrated and accurately navigated to provide real-time environmental data; · Fundamental exploitation of the advances in ocean acoustics, oceanography, and signal processing; Robust ocean engineering for their deployment; Integration of communications, navigation, and high-speed computation; and · Highly trained operators. At the end of the Cold War the merging of these components showed prom
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From page 14... ...
The acoustic field has a three-dimensional structure that can be resolved only with multidimensional ar rays. The spatial and temporal coherence of both submarine signals and ambient and reverberation noises is the fundamental acoustic attribute that will enable the development of high-performance ASW signal processing systems.
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From page 15... ...
In radar this is termed space-time beam forming and leads to impressive noise suppression for both clutter and jamming, yet it has not been explored in sonar. Coherent sonar signal processing can be considered a generalized form of matched filtering, so that spatial and temporal replicas, or matching signals, are required for implementation.
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From page 16... ...
Although there has been progress toward greater integration into the sonar system, such as the real-time implementation of the parabolic equation and on-line ambient noise models, the environmental data now available from real-time sensors, databases, and satellite observations are not well utilized for optimizing sonar performance. More importantly, oceanographic data generally are not brought to bear on sonar signal processing problems.
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From page 17... ...
The rapid pace of development in acoustics, oceanography, signal processing, and ocean engineering relevant to sonar applications should enable a shortening of the development time between the demonstration of the engineering feasibility of advanced sonar techniques and their implementation. The long development times for new sonar systems, which have in the past often spanned a decade or more, are no longer acceptable long development times do not allow the Navy to respond rapidly to changing missions and needs.
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From page 18... ...
Towed arrays, forward spherical and cylindrical arrays, and conformal arrays from both submarines and surface ships provide tactical ASW. Since these systems are mobile and can be deployed rapidly in areas of potential conflict, they most likely will form the major components of future ASW systems.
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From page 19... ...
Although it is unlikely that the size or number of sensors on these arrays can be increased, their performance can be improved with state-of-the-art signal processing. Full-area, conformal arrays distributed over a large extent of a submarine offer wide apertures and are not encumbered by the tactical constraints associated with long towed arrays.
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From page 20... ...
This can be minimized by incorporating accurate test range and structural acoustic models into the array processing algorithms. The technology for towed arrays has two major components that ultimately limit their size and number: the sensors themselves and the signal telemetry.
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From page 21... ...
There are also a number of potentially useful properties of deformed towed arrays that deserve exploration. The right-left ambiguity can be distinguished with horizontal deformations, and the introduction of vertical tilt leads to the possibility of using matched-field processing.
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From page 22... ...
The coverage that a fixed system can provide against modern quiet threats will not have basin scales, but the performance can be maximized with imperatives described earlier. Wide apertures with sensor numbers far exceeding those of SOSUS, the use of fully coherent processing with accurately navigated arrays, adaptive beam forming, and the exploitation of Doppler all can be used with the same measures of effectiveness.
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From page 23... ...
In shallow water and on the shelf, strong horizontally anisotropic internal waves driven by tidal and topographic forcing, usually with a diurnal period, can modulate sound speed profiles dramatically. In upslope-downslope geometries these can precipitously interrupt surface duct propagation and impact coherences through mode coupling and/or ray path fluctuations.
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From page 24... ...
. The twin line SURTASS experiment used two parallel towed arrays with a sensor positioning system.
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These and other experiments suggest some of the critical issues in acoustics, oceanography, and signal processing for future ASW systems. Acoustics · Coherence scales.
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From page 26... ...
Oceanographic models for the sea surface, internal waves, and bathymetry exist; however, they require further development to extrapolate their use down to acoustic wavelength scales and environmental data to constrain the parameters in the models. Signal Processing · Algorithms for wide-aperture, high-density arrays.
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From page 27... ...
The emphasis in signal processing is usually on the coherent front-end beam forming and matched filtering, yet the postprocessor that performs an incoherent combination of these outputs across frequency for a threat spectrum and over time for a track hypothesis provides a substantial fraction of the overall processing gain. In addition, the postprocessor provides the track parameters for target motion analysis solutions.
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From page 28... ...
The following technologies are unique to the Navy ASW mission and may require direct Navy support for their further development: . sensor spacing Array technology Low-cost horizontal, vertical, and multidimensional arrays with dense Reliable array deployment and handling Modular, fiber-optic data telemetry · Environmental data acquisition High-resolution environmental databases Assimilation of real-time oceanography Real-time satellite data · Processing hardware and software Modular, commercial off-the-shelf (COTS)
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From page 29... ...
Yet, addressing several of the imperatives for passive ASW that exploit fully coherent processing with large-aperture arrays requires a facility where these research issues can be addressed. Experiments with fixed arrays are necessary because towed arrays introduce both motion effects and positional variability, which complicate measurements and analysis.
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From page 30... ...
Nevertheless, passive detection ranges for these low-speed modern submarines have shrunk from hundreds of kilometers to only a few kilometers. These trends, illustrated in Figure 1.1, if continued into the next 35 years will lead to essentially undetectable submarines and will reduce ASW capabilities to close-proximity detections and transient or higher-speed situations.
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From page 31... ...
At the same time, relatively cheap but high-performance sensor and telemetry or connection concepts are maturing, based on fiber optics for both sensors and telemetry and MEMS or other miniaturized sensor concepts. These developments enable not only the processing of more signals with higher bandwidths from more sensor elements with ever more sophisticated algorithms, but also exploitation of the details of the local ocean environment through temporally and spatially coherent processing as well as spatial signal replica/adaptive beam forming the so-called matched-field processing.
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From page 32... ...
In addition, receiver and processing advances in passive acoustics will directly benefit the active side as well. Typical active acoustics system concepts are shown in Figure 1.2.
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From page 33... ...
UAVs could also act as communications relays or weapon deliverers. Overall, active acoustics could confound an adversary without putting manned platforms at risk.
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From page 34... ...
NONACOUSTIC ASW: A NEEDED COMPLEMENT TO ACOUSTICS Based on the current technical understanding of nonacoustic submarine signatures and their detectability under various operational and environmental conditions, nonacoustic ASW concepts will, in general, complement acoustics in at least the following ways: . regimes: and Exploit shallow submarine operations, particularly when acoustic detection might be degraded, thus inhibiting an adversary from using an important part of his operating envelope and denying him a safe haven from acoustics.
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From page 35... ...
; and 3. In situ detection of the turbulent wake, contaminants contained in the turbulent wake, or the internal wave field using sensors mounted on or towed from surface ships or submarines.
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From page 36... ...
Little work, however, has been done on the vulnerability of acoustic communications networks to acoustic jamming or on covert underwater communication. UNDERSEA WEAPONS A FUTURE PERSPECTIVE The continuing evolution of the potential submarine threats facing U.S.
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From page 37... ...
In the near- to mid-term time frame, the focus will be on improving the performance of undersea weapons in complex, littoral environments and scenarios against an increasingly stealthy submarine target equipped with sophisticated countermeasure devices for thwarting a weapon attack. Insertion of new technology in signal processing, detection and classification, sensors, and guidance algorithms is planned.
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From page 38... ...
The enabling technologies for such a concept might include the following: · A high-bandwidth sensor data network and fusion capability (i.e., an undersea cooperative engagement capability ICECAP; · A rapid-response, high-speed airborne delivery vehicle; · A UAV with long loiter time carrying a shorter-range, high-speed delivery vehicle; . 1ng; or Rapidly deployed distributed sensor field on datum with fused process · Off-board guidance and control of the weapon to the close-in vicinity of the target, potentially using a high-bandwidth data communication to the weapon that permits wide-band, intersensor processing between a weapon and off-board sensors.
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From page 39... ...
Technology advances in unmanned systems will allow the proliferation of sensors over the undersea battle space without exposing manned platforms to unacceptable risks. Unmanned air, surface, subsurface, drifting, and fixed platforms will act as force multipliers to provide a highly integrated network to address the ASW problem.
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From page 40... ...
Examples of these concepts with their requisite enabling technologies are presented in Table 1.2. It is evident that the TABLE 1.2 Possible Future ASW Concepts Concept Enabling Technologies Submarine detection, instant localization from space or air vehicles Hull Wake Surface effects Picobuoys (highly distributed floating sensors)
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From page 41... ...
· Incorporate engineering experience connected with the manufacture and deployment of large towed arrays gained by the offshore oil exploration industry.
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From page 42... ...
· Pursue robust enabling technology for protecting surface ships and submarines against threat torpedoes, such as antitorpedo weapons and advanced countermeasure devices.
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