基于极低频电磁场的浅海运动目标空中探测机理研究

When voyaging in the sea, due to the presence of dissimilar metal corrosion current and the rotation of the propeller ,underwater vehicle can produce extremely low frequency (ELF) electromagnetic field of periodicity. The lateral waves of the ELF electromagnetic field decay slowly when propagating along the interface, it is considered to be one of the most promising signature for remote sensing among the vehicle’s electromagnetic field. Shallow water vehicle detection mechanism in air based on ELF electromagnetic field is studied in this project. First, a prediction model for ELF electromagnetic field source based on the stratification characteristic of shallow water is built. Using this model, the field strength of ELF electromagnetic field source is inverted from the measured data; second, a near field propagation losses model for ELF electromagnetic waves is built to calculate the electromagnetic field at different distances in air; third, the background noise of several sea areas are tested, then analyzed with statistical and frequency spectrum method. Combined with the noise level of the sensor, the detection range for the underwater vehicles can be estimated. At last, show water tests are carried out to demonstrate the detection range could be over kilometers. The research of this project can provides theoretical and experimental basis for the application of the ELF electromagnetic field detection technology in airborne, surface warship, fixed monitoring stations, etc., and have great theoretical significance and engineering application value.

水下目标航行时，由于自身异金属的存在会形成腐蚀电流，螺旋桨旋转调制腐蚀电流产生周期性的极低频（ELF）电磁场，其侧面波分量沿分界面传播，衰减速度较慢，是水下目标电磁场中最有潜力被应用于远程探测的特征信号之一。因此，本项目对基于ELF电磁场的浅海运动目标空中探测机理展开研究。针对浅海环境的分层特性，建立浅海环境中水下ELF电磁场场源大小的预估模型，利用该模型对实测数据进行反演，得到ELF电磁场场源大小；建立浅海中激发的ELF电磁波的近场跨界面传播损失模型，得到海面上空不同位置处的电磁场；测试多个海域的背景噪声并进行统计分析和频谱分析；再结合目前传感器的噪声水平，计算出能够对水下目标进行探测的范围，最后通过海上试验验证实现千米级探测距离的可行性。该项目的研究可为ELF电磁场探测技术在飞机、水面舰及海上固定检测点等平台上的实际应用提供理论基础和试验依据，具有重要的理论意义和工程应用价值。

隐身与反隐身一直是水下作战的重要方面，我国海军对水下运动目标的搜索和监视能力较为薄弱，而传统的声探测及磁异常（利用目标的铁磁性，属于静态场）由于自身缺陷，在浅海应用时效果并不理想。目前急需发展新的探测方法来保障我国海洋安全。项目组前期试验中发现水下目标航行时由于螺旋桨旋转调制腐蚀电流会产生极低频电磁场，并辐射到空气中。为此，该项目对基于极低频电磁场的浅海运动目标空中探测机理展开研究。.围绕研究目标，首先建立了浅海环境中水下极低频电磁场场源大小的预估模型，利用该模型对实测的轴频电磁场分量进行了反演，得到极低频电磁场的场源大小；再建立了浅海中激发的极低频电磁波近场跨界面传播损失模型，据此能够计算出海面上空的电磁场分布；接着测试了多个海域的背景噪声并进行统计分析和频谱分析，至此可以确定海面上空不同位置的信噪比；再结合目前磁传感器的噪声水平，可以估算出能够对水下目标进行有效探测的范围，最后通过海上试验验证在空中能够实现对水下运动目标千米级的探测距离。.项目执行中解决了两个重要的科学问题：（1）摸清了水下水下运动目标的轴频电磁场场源特性，包括产生极低频电磁场的机理、该电磁场的频率范围、基频与目标航速的关系、该场源的等效模型及大小；（2）解决了分层介质中极低频电磁波的近场跨界面传播特性这一难题。通过建立分层模型，采用数值计算方法，准确计算了极低频电场的跨界面传播损失，并通过了实验验证。该项目的顺利完成，为促进极低频电磁场探测技术在飞机、水面舰及海上固定检测点等平台上的实际应用提供理论基础和试验依据。