Research On Underwater Low Frequency Electromagnetic Wave Propagation And Internal Wave Sea Electromagnetic Scattering

With the development of military technologies from different countries in recent years,it has been a dominant strategical tendency to compete for marine resources.Military technology not only contains the hard-power equiments' development and updating like nuclear weapons,but the sea communication,underwater detection,navigation and aviation are also involved.Based on the background,this paper mainly studies the underwater electromagnetic wave propagation and scattering characteristics.In the frequency range of 30Hz~300KHz,the induced magnetic field generated by underwater targets and the low frequency field characteristics of magnetic dipole at the homogeneous half-space interface are also been studied.When the sea contains internal waves,the effect on the electromagnetic scattering of sea is observed from the change of scattering coefficients and of the doppler spectrum respectively.The main contributions of this paper are as follows:First of all,the electromagnetic waves' propagation characteristics in seawater are expounded and elaborated based on its basic physical properties,including some basic electromagnetic parameters: the induced electromagnetic field,the skin depth,field intensity attenuation and so on.And the conductivity distribution and its transmission characteristics in the interface of the two layers of sea surface are analyzed.Moreover the generation conditions and movement characteristics of the internal waves in the sea is briefly introduced.Under the conditions of electromagnetic wave irradiation at low frequencies,the induced electromagnetic fields generated by underwater conductor targets are taken into considerations as a following part to the expansion of the first part.The whole process starts from the establishment of the incident field model,and the changing properties of the induced magnetic field are discussed then,finally the distribution of induced current on the target surface is evaluated.As for the interface divided by lossless and lossy media of which homogeneous half-space is composed,the analysis abo ut the near-field propagation characteristics of the magnetic dipole at low frequency is based on the derivation of the Sommerfeld integral equation,and the results by our method have been compared with that given by NBS(National Bureau Standards)literature.The impact of internal wave on the electromagnetic scattering characteristics of sea surface is investigated.It is noted that there are few researches to study the influence of the internal wave on the scattering coefficients as well as the Doppler spectrum home and abroad.Based on the Kd V equation,the model of the isolated internal wave propagation is established.After combining facet model based on two-scale method with modulation effect of the surface wave spectrum of the sea considering the existence of internal waves,the influence of the existence of internal waves on the electromagnetic scattering characteristics is calculated,and moreover the impact on the sea surface scattering coefficients and Doppler spectrum along with the change of different sea conditions and various internal wave parameters are analyzed.Of course,this paper only focuses on the ideal model to calculate and analyze,however the actual radiation source and medium are very complex,which means that further researches on the target conductor,layered interfaces and internal wave s' properties need to be done in the future for practical applications.O nly in this way can we better use this for real combat.