![]() Signals of several modes may be separated, and after correction for arrival time and phase, these filtered normal modes may be recombined to obtain a compressed and enhanced signal. Several on mode filtering methods are possible source ranging and depth estimation in the shallow water wave guide. Hence, due to modal interference in a waveguide, conventional beamforming techniques cannot be used. The spatial structure of the accoustic signal in the waveguide formed by the surface and bottom in shallwo water is significantly different from the that in the free field of deep water. Hence, mode filtering is a useful approach for investigating multipath fields in shallow water. This results in elongated, low amplitude signals.įurther, because of the non-uniform effects of the interaction-e.g., the higher-angle modes suffer greater attenuation-only several modes may be needed to characterize the sound field. Because of interaction with the bottom, long range sound propagation in shallow water is characterized by separation of the constituent modes as a result of the differences in modal group velocities. Consequently, long-range reverberation in shallow water is far more complex than the deep-water case. This "optimum frequency" regime arises from the combined effect of the volume attenuation at the higher frequencies and the loss due to interaction with the sea bottom at the lower frequencies.īecause of the proximity of the boundaries in shallow water, multipath transmission and multi-angle scattering from the sea bottom are concomitant characteristics of shallow-water acoustic reverberation. 1997) it is well known that as a result of the selective frequency effect of the shallow-water sound channel, a band of frequencies exist in which the propagation is enhanced (i.e., the transmission loss is relatively small). As reported in ONR Ocean Science and Engineering Newsletter # 2 (Feb. Operating in the shallow waters of littoral areas imposes a different accoustic environment for which previous submarinen classes were optimized. ![]() With a focus on the littoral battlespace, the New Attack Submarine has improved magnetic stealth, sophisticated surveillance capabilities, and Special Warfare enhancements. The primary design driver for the NSSN is acoustic quietness equal to that of the Seawolf, even at the cost of reducing maximum top speed. While the 688-I submarines are noisier than the improved Russian Akula class, the Seawolf is quieter than Akula and the upcoming Russian SSN-P-IX class. On the other hand, the NSSN is expected to be as quiet as the Seawolf, will incorporate a vertical launch system and have improved surveillance as well as special operations characteristics to enhance littoral warfare capability. Compared with the Seawolf, the NSSN is slower, carries fewer weapons, and is less capable in divingĭepth and arctic operations. Smaller hull while military performance has been maintained or improved. SEAWOLF (SSN-21)-Class quieting has been incorporated in a The New Attack Submarine is designed for multi-mission operations and enhanced
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