Sonar Performance Models Research Articles

Turbidity in future high-frequency sonar performance models

Current sonar performance models are incapable of accurately predicting the performance of high-frequency sonars in highly variable turbid coastal waters. There is therefore a requirement for improved models incorporating the additional effects in such environments. Turbid coastal waters are characterized by relatively high levels of suspended particulate matter, the presence of which leads to increased attenuation through viscous absorption and scattering, leading to a significant reduction in the detection range of high-frequency active sonars at moderate concentrations. The additional attenuation mechanisms have been incorporated into a propagation-loss model and the effect on detection range has been investigated. The additional attenuation processes are influenced by the ambient temperature, pressure, and salinity, and the effects of these parameters on the total attenuation in seawater containing suspended mineral particles has also been investigated. The results presented demonstrate that the effects of suspended particulate matter should be included in future high-frequency sonar performance prediction models in turbid environments. Temperature is found to be an important factor influencing the attenuation, and the local temperature should therefore be used in performance calculations. [Published with the permission of the Controller of Her Britannic Majesty’s Stationery Office.]

The status of Naval underwater acoustic modeling

Results from a survey of recent developments in Naval underwater acoustic modeling are compared with those of two previous surveys conducted at 8‐year intervals [P. C. Etter and R. S. Flum, Sr., J. Acoust. Soc. Am. Suppl. 1 65, S42 (1979); P. C. Etter, J. Acoust. Soc. Am. Suppl. 1 82, S102 (1987)]. All surveys cover basic acoustic models and sonar performance models. Basic acoustic models include propagation, noise, and reverberation models. Sonar performance models integrate basic acoustic models, signal processing models and supporting databases into cohesive operating systems organized to solve the active or passive sonar equations [P. C. Etter, Underwater Acoustic Modeling (Elsevier, Amsterdam, 1991); 2nd ed. (Chapman & Hall, 1995)]. Summary tables identify and highlight noteworthy characteristics of 83 propagation models, 15 noise models, 14 reverberation models, and 14 sonar performance models. These surveys provide a retrospective view of modeling developments over the past two decades and document a 160% increase in the number of models that are now available for applications in sonar technology. This updated baseline also suggests future directions for Naval modeling in an era of defense conversion including new applications in oceanographic research.

Remote sensing of environmental parameters

This paper describes a prototype environmental parameter sampling system and the problems it is intended to address. Increasingly sophisticated sonar performance models are being developed in support of advanced sonar system. A graphic portrayal of the simulated performance of a notional sonar system is presented as an example of the sensitivity of a simulation to the input environmental parameters including the volume scattering profile. The prototype environmental sampling system is configured to provide an estimate of the volume scattering profile. Operationally, this profile is not available to simulation users. The prototype environmental parameter sampler will be used to demonstrate how simulation errors due to this critical environmental input can be eliminated. The use of the microcomputer based prototype hardware as a basis for estimating other environmental parameters will also be presented. [Work supported by NAVSEA.]

Empirical results from frequency-scanning nonlinear sonar in deep water

The wide-bandwidth capability of nonlinear sonar allows conduction of ocean bottom and sub-bottom investigations at many frequencies. In order to obtain a wide-bandwidth ocean bottom signature spectrum, a system has been implemented which serially translates a coherent frequency source to five different channels, f + Δf, f + 2Δf, f + 3Δf, f + 4Δf, and f + 5Δf. In the ocean, the nonlinear mechanism convolves a second selected primary frequency f with each appearing channel. The low sonar frequencies Δf, …, 5Δf efficiently propagate to large ocean depths. The returning signals provide an ocean bottom and sub-bottom frequency spectrum. Theoretical predictions were presented in the paper “Frequency Scanning Nonlinear Sonar Performance Modeling,” by John A. Birken at the Ocean '74 Conference. In March 1974, William Konrad, NUSC/NL, successfully demonstrated his 0.8-m2-aperture nonlinear array. His empirical data, which were recorded on tapes, provide a source of empirical information to compare with the performance model. Sub-bottom predictions versus frequency have been found to agree significantly with the collected data.