Background 111 Setting

Underwater acoustics entails the development and employment of acoustical methods to image underwater features, to communicate information via the oceanic waveguide or to measure oceanic properties. In its most fundamental sense, modeling is a method for organizing knowledge accumulated through observation or deduced from underlying principles. Simulation refers to a method for implementing a model over time.

Historically, sonar technologists initiated the development of underwater acoustic modeling to improve sonar system design and evaluation efforts, principally in support of naval operations. Moreover, these models were used to train sonar operators, assess fleet requirements, predict sonar performance and develop new tactics. Despite the restrictiveness of military security, an extensive body of relevant research accumulated in the open literature, and much of this literature addressed the development and refinement of numerical codes that modeled the ocean as an acoustic medium. This situation stimulated the formation of a new sub-discipline known as computational ocean acoustics. Representative developments in computational ocean acoustics have been documented by Merklinger (1987), Lee et al. (1990a-c, 1993) and Lau et al. (1993).

As these modeling technologies matured and migrated into the public domain, the private industry was able to apply many aspects of this pioneering work. Subsequently, there has been much cross-fertilization between the geophysical-exploration and the sonar-technology fields as the operating frequencies of both fields began to converge. Recently, acoustical oceano-graphers have employed underwater acoustic models as adjunct tools for inverse-sensing techniques (see Section 1.6) that can be used to obtain synoptic portraitures of large ocean areas or to monitor long-term variations in the ocean.

Underwater acoustic models are now routinely used to forecast acoustic conditions for planning at-sea experiments, designing optimized sonar systems and predicting sonar performance at sea. Modeling has become the chief mechanism by which researchers and analysts can simulate sonar performance under laboratory conditions. Modeling provides an efficient means by which to parametrically investigate the performance of hypothetical sonar designs under varied environmental conditions as well as to estimate the performance of existing sonars in different ocean areas and seasons.

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