TOA positioning algorithm of LBL system for underwater target based on PSO

For the underwater long baseline(LBL)positioning systems,the traditional distance intersection algorithm simplifies the sound speed to a constant,and calculates the underwa-ter target position parameters with a nonlinear iteration.However,due to the complex underwater environment,the sound speed changes with time and space,and then the acoustic propagation path is actually a curve,which inevitably causes some errors to the traditional distance intersection positioning algorithm.To reduce the position error caused by the uncertain underwater sound speed,a new time of arrival(TOA)intersection underwater positioning algorithm of LBL system is proposed.Firstly,combined with the vertical layered model of the underwater sound speed,an implicit positioning model of TOA intersection is constructed through the constant gradient acoustic ray tracing.And then an optimization function based on the overall TOA residual square sum is advanced to solve the position parameters for the underwater target.Moreover,the particle swarm optimization(PSO)algorithm is replaced with the tra-ditional nonlinear least square method to optimize the implicit positioning model of TOA intersection.Compared with the traditional distance intersection positioning model,the TOA intersec-tion positioning model is more suitable for the engineering practice and the optimization algorithm is more effective.Simulation results show that the proposed methods in this paper can effectively improve the positioning accuracy for the underwater target.

Elastic constants and softening of acoustic mode in K_2SnCl_6 crystal studied by Brillouin scattering

In this paper we present the Brillouin Scattering measurements of the longitudinal and transverse sound velocities for the hexahalome-atllate K2SnCl6 at room temperature . The elastic constants , refractive index , volume compressibility are determined from the Brillouin line shifts. Furthermore, the sound velocity in the [111] direction is investigated as a function of temperature 252K<T<270K . An acoustic adrupt change of the c11+2c12 mode is observed as the temperature approaches 256K from above, which has been analysed by means of the Pippard relations. The conclusion is that K2SnCl6 undergoes first order phase transition near T=256K. This acoustic anomaly can be interpreted by the nonlinear coupling of the elastic strain field to the fluctuation of the soft-mode coordinate.

Blind equalization of underwater acoustic channel using a combined constant modulus algorithm

A kind of Combined Constant Modulus Algorithm (CCMA) is presented to compensate the defects of the Constant Modulus Algorithm (CMA) and the Sign Error CMA (SECMA). And CCMA is applied to the equalization of the underwater acoustic channel (UWAC). Based on the decision of the equalizer’s output, its iteration process switches between