| Recently,the focus of the economic and military development strategies of many countries has gradually extended to the marine field with the rapid development of the world economy.Among them,the detection technology of underwater targets/objects has received much attention.Presently,there are sonar,laser or radar,geomagnetic anomaly,visible light or infrared imaging detection technology of underwater ferromagnetic objects such as underwater cruisers,shipwrecks,seabed metal minerals,caves,etc.Because of the development of various silencing technologies,the echoes of underwater targets/objects are very close to the sea background noise,sonar detection methods are facing severe challenges.Considering the shielding characteristics of high-frequency electromagnetic waves by seawater,it is more difficult to detect underwater targets/objects in the deep water by actively emit high-frequency electromagnetic waves such as laser/radar detection methods.There are many large-scale transmission electricity networks of different sizes all over the world,which can emit steady power-frequency electromagnetic wave to the surroundings.Thence,the detection method of power frequency electromagnetic wave will make an important role in the detection and localizationing of underwater targets/objects.Starting from basic theories such as Maxwell's equations,the generation mechanism,the propagation characteristics of power frequency electromagnetic wave yieled by the power line transmission network,and the properties of abnormal distortion of the timevarying background electromagnetic fields caused by ferromagnetic objects were analyzed;and the feasibility of power frequency electromagnetic detection of underwater ferromagnetic objects was revealed through a simulation example and field tests.Taking the East-Central-South-Northeast-Mengxi's power line transmission network of China as the source of electromagnetic radiation,underwater cruisers as detection targets,seawater and air as transmission media,the power frequency electromagnetic simulation model of an underwater ferromagnetic object under the action of the power network was established.Through finite element calculation of the above simulation model,the simulation results of the power frequency electromagnetic anomalies caused by underwater ferromagnetic objects in different geographical localizations and different observation altitudes and the influence of target characteristics on simulation results were discussed.Based on the island detection platform,a triangular localizationing method was proposed;based on the space detection platform,the scanning cross-localization method proposed by predecessors was optimized.Then the influence of disturbance factors on the detection process such as power network harmonics,power network phase changes,sea waves and surface ships were simulated and analyzed,and corresponding interference discrimination /suppression methods were given.Finally,this paper summarized the research work and pointed out the issues that should be aware of in propelling the research work of future. |
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