Use of SALT tables for rapid calculation of sound angle, level, and travel time

Abstract

There are cases where a very quick calculation of sound propagation is required. One example is a real-time torpedo simulator where only a fraction of a second is available to determine sonar returns. Another example is a bistatic reverberation model where thousands of scattering elements must be included in a realistic model. A SALT table is a list of sound angle, level, and travel time listed as a function of range from the source or receiver. The number of tables used depends upon available computer storage and time available to access the data in the tables. This paper will discuss two algorithms for calculating SALT tables. In one method, the table is defined by the number of bottom reflections or ray turnunders. In the second method, the tables are numbered according to order of calculation. Several examples will be given showing reasonable agreement between calculations using SALT tables and those using more exact methods.