Research On Detection Technology Of Underwater-Object Employing Power Frequency Electromagnetic Field

In recent years,the underwater target detection technology has received the attention of major military powers in the world.For the underwater targets such as underwater vehicles,shipwrecks,and caverns,many technical approaches have been developed,such as radar detection technology,geophysical magnetic-field detection technology,laser detection technology,and wake detection technology and so on.The typical geophysical magnetic-field detection demonstrates remarkable characters including all-weather,large detecting range,and high positioning accuracy.Currently,the research on the underwater target detection according to electro-magnetic field characteristics,is mainly focused on the key factor: analyzing the magnetic anomaly generated in used metal materials in the geomagnetic field.Considering the cases that the geomagnetic field can be regarded as a constant field,and the geomagnetic distribution of different regions shows the difference,the target detection performance based on geomagnetism is susceptible to environmental factors,and thus it is urgent to develop new high-performance electro-magnetic detection means.So far,large-power transmission networks of various scales have been set up around the world.There are stable power frequency electromagnetic wave fields in the surrounding environment of the network.The typical wavelength is up to 6000 km,which is less affected by the attenuation of environmental media such as seawater.Therefore,the use of power frequency electromagnetic wave field will show special value in detecting and locating underwater targets.The basic methods of detecting underwater targets based on the power frequency electromagnetic wave-field are mainly researched in this thesis,and mainly involves the modeling and simulation of underwater targets operated by large transmission network,the differentiation of interference signals,and the detecting and locating algorithms for several platforms.Based on the relationship between Maxwell's equation and electromagnetic induction,the propagation characteristics of electromagnetic field in seawater medium and the mechanism of generating power frequency electromagnetic wave field in distributed large-scale transmission network and the mechanism of electromagnetic anomaly in underwater background are analyzed.Taking the transmission network of East-China Central-China and South-China as the electromagnetic radiation source,both the underwater vehicle and the wreck ship are taken as two typical underwater targets,and the simulation models of the underwater target power frequency electromagnetic field under the distributed transmission network are established.In this paper,the simulation data is further collated and analyzed to reveal the regularity of the anomalous propagation of power frequency electromagnetic signals caused by underwater targets.The feasibility of using the power frequency electromagnetic wave-field generated by the large distributed transmission networks to detect underwater targets under the condition of power grid load fluctuation and geomagnetic field interference is demonstrated.Based on the simulation analysis,a power frequency electromagnetic wave field detection and location method suitable for ground&air platform is proposed.Finally,the research work is summarized and pointed out the problems that should be paid attention to further advance the research work and give a prospect of technology development.