The impact of bottom backscatter strength modeling on active sonar optimal frequency calculations.

Abstract

For many active sonar problems, there exists an optimal frequency—one at which detection range maximized. The optimal frequency can be calculated using a frequency dependent analytical sonar equation to solve for the detection range, defined as the largest range with positive signal excess. The frequency with the maximum detection range is the optimal frequency. An advantage of this approach is that it combines all of the sonar equation terms into a single quantity. It might seem that such a frequency will not exist because propagation loss tends to increase with increasing frequencies, so performance might decrease monotonically with frequency. However, other terms in the sonar equation are also frequency dependent. For example, Knudsen or Wenz curves show that noise levels generally decrease with frequency, while source level and target strength may be complicated functions of frequency. In shallow water, active sonar may be reverberation limited rather than noise limited, but standard Lambert scattering strength models are frequency independent. New, more accurate bottom backscatter strength models have frequency dependence, which will impact the optimal frequency calculation. This approach demonstrates one operational impact of improved reverberation modeling, and quantifies the performance degradation caused by a suboptimal frequency selection.