| Popis: |
The seawater and seabed interface is the basic electric property interface of the shallow sea environment, and has a direct influence on the propagation and attenuation of the underwater low frequency electromagnetic field. It is necessary to analyze the influence of the electric property interface on the electromagnetic field in order to improve the measurement accuracy of marine underwater electromagnetic field tests and the performance of underwater electromagnetic communication. In this thesis, the physical mechanics of the interface influence is analyzed and interpreted by use of the interface influence factor on basis of the image method principle. The shallow sea is simplified as the air, seawater and seabed three layers homogeneous and isotropic conducting media model; and, the equation formula of electromagnetic field excited by the harmonic horizontal electric dipole in the seawater is presented. Through numerical testing, the spatial distribution and attenuation characters of the electromagnetic field excited by the harmonic horizontal electric dipole are investigated, and the influences of the interface on the electromagnetic signatures are analyzed quantitatively. The results show that the horizontal component amplitude of the underwater electric field increases and the vertical component amplitude decreases, apparently because of the high resistance property of the seabed. The transverse component amplitude of the underwater magnetic field is reduced and the vertical component amplitude is unchanged. The attenuation rate of the electric field horizontal component along the longitudinal direction with the interface is less than the attenuation rate without the interface. On the sea bed, the electromagnetic field attenuation rate decreases sharply with the decrease of seabed conductivity. On the basis of theory and numerical analysis, the influence model of the seawater and seabed interface is constructed by use of a curve fitting method. The research conclusions have wide application prospects in the interface influence correction of vessel underwater electromagnetic field measurement, and also the long distance measurement of the underwater electromagnetic field in the sea environment. |
