Broad bandwidth, high level acoustic energy flux density over the frequency range of interest, and flexible deployment are characteristics of underwater explosive sound source. It achieves good results when being widely applied in fields like research of underwater sound, inversion of sea bottom geoacoustic parameters and underwater acoustic countermeasure.
Explosive sound sources have same clear advantages in comparison with conventional-pulsed electroacoustic sonar sources. The desirable side of explosive sound sources is the fact that they are mobile in the sense of being free of connecting cables. And therefor it can be easily launched and detonated at any depth.
They yield a short high-power broadband pulse that is useful when range resolution is important. They are nondirectional and need not be beamformed to send an adequate amount of acoustic energy in the direction of the target. For these reasons explosive sources in sonar can perform well in research studies and air-dropped applications where their mobility and depth flexibility are of paramount importance.
In the recent research, scientists from the Institute of Acoustics of the Chinese Academy of Sciences systematically study the underwater target localization and parameters (azimuth and range) estimation by the method of utilizing explosions as underwater sound sources.
By deploying explosive sound sources between sonar and underwater target as active sound signals, and using sonar array to receive the explosive signals scattered from the target, the underwater target can be detected.
If the location of explosive sound source is already known, it is possible to estimate the azimuth and range parameters of the target. It can be achieved in the means of measuring the arrival azimuths of direct explosive sound signal, the signal scattered from the target, as well as the arrival time difference between the two signals.
The narrow beam reverberation model of the target echo signal and Coherent Signal-Subspace (CSS) method are applied to estimate the target azimuth in reverberation background. Estimation errors of target azimuth is studied and proved to approximately meet Gauss distribution. Deploying explosive sources of large spectrum levels can improve the azimuth estimation accuracy and enlarge azimuth interval with high estimation accuracy.
The mathematical expression of target range error is deduced and target range error is proved to meet Gauss distribution. And then, the variance formula of target range error is derived. A series of simulations are made to study the target range errors due to different bistatic angles, different explosive source ranges or different target azimuth errors. Some measures which can reduce the estimation errors of target ranges in practical usage are obtained from the results of simulations.
It has been confirmed by the data processing results of simulations and lake experiments that the method of utilizing explosions as underwater sound sources can accurately locate underwater target at a long distance on the condition of a certain underwater explosion range error.
The varying of explosive sound source range has little impact on the precision of target range estimation if the target azimuth and explosive sound source range error are kept unchanged. Choosing suitable deploying azimuths of explosive sound sources can reduce estimation errors of target ranges.
The analysis of estimation errors and measures to improve estimation accuracies of target parameters will help sonar engineers to deal with target localization problems in actual operations, and to further perfect the design of localization systems. Besides, the deduced target range error function and variance formula of target range error can also be utilized in bistatic and multistatic sensors (sonar, radar, etc.) applications.
YAN Sheng, WEI Xiaojun, HAO Chengpeng, MA Hui, YAN Shefeng. Target Localization and Parameters Estimation by Sonar System with Explosions as Underwater Sound Sources. Chinese Journal of Acoustics (Vol. 35, No.4, pp.416-430, 2016).
Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China