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Environmental Factors, Dynamics of Quiet Targets in Confined Areas, Crew Sizes, Operator Limitations, Data Quantities, New Technologies Dictate Application of New Solutions
For the purposes of this article, shallow confined waters are defined to mean shallow waters in which there are vertical boundaries that influence acoustic conditions and/or ship maneuvers. The material presented is based in many ways on the concepts developed for the Swedish YS2000 VISBY project, for which Computing Devices Canada is the prime contractor for the underwater warfare suite. That project goes beyond the scope of this discussion in that it integrates a complete mine-- countermeasures system with the ASW capability to create a very flexible total undersea warfare capability. Mine aspects are not being addressed in this article; we shall focus on ASW.
Design for Shallow-Water ASW
Most navies contend that their own shallow coastal waters are unique: they are correct! There are big differences between the hot waters in the Tasman Sea and variable salinity of the Baltic or the high salinity of the Persian Gulf. The sonar designer's problem relates to the development of an effective design aimed for a general class of problems where all environments are different.
However, common to most shallowwater environments are larger reverberation levels and higher propagation-loss levels than deep water. Like deep-water problems, shallow water still presents the sound-speed layering with depth. Additionally, consider the percentage variation in water depth versus range and azimuth in shallow water, where depths can vary from 50 meters to 150 meters and back to 50 meters over a distance of a few kilometers. Thus submarine hiding spots abound. Coastal sandbanks, bottom type changes, and exposed sub-bottom layers all conspire together to make the shallow water problem confusing to the operators. Ancient riverbeds can transform a shallow-water problem into confined-waters problem analogous to that of ASW in an archipelago or a fjord.
There are other common shallowwater acoustic factors that have a strong influence on ASW sonar system design, for example, ambient noise characteristics. Unlike the deep-water situation where the shipping component of ambient noise is based on the average of a large number of sources that tend to give general characteristics, the shipping component of ambient noise in littoral waters is ever shifting in directionality and...