Effective magnetic surveying with multi-thruster underwater vehicles

磁力计用于记录局部磁场的强度和方向。当安装在小型和廉价的自主水下航行器上时，磁力计提供了一种创建磁性地图的方法，可用于定位埋藏的矿物。然而，为了生成有用的地图，需要进行显著的校正以去除车辆的磁足迹-车辆航向和车辆推进器在局部场中产生波动，该波动主导了由局部掩埋特征发射的信号。2016年，海洋地球物理学（OFG）成功开发了可安装在自主水下航行器（AUV）上的自补偿磁力计（SCM）。补偿系统利用AUV推进器的状态知识和推进器电磁特性的半经验模型来估计真实的时间内的航行器的完整磁足迹，并将其从测量信号中去除。为了使SCM适用于其他应用，例如定位沉船、未爆炸弹药、管道或通信电缆，需要增强补偿方法以用于遥控水下航行器（ROV）; ROV使用多个推进器的布置以在纵荡、摇摆、升沉和偏航中同样良好地移动（不像AUV使用单个推进器来产生纵荡运动）。为了修正OFG SCM校正算法，使其适用于多推力器电动ROV，必须推导出总推力器感应磁场的模型。该模型可用于确定校正方程的结构，并设计校准机动和优化算法以自动确定补偿方程的系数。在目前的项目中，正在开发建模、校准和优化程序，并使用小型Saab-SeaeyeTM进行现场测试。新的SCM系统建成后，将使考古学家、警察、港务局、地质学家和海洋学家能够对水下地形进行有效和有用的磁力调查。

Magnetometers are used to record the intensity and direction of local magnetic fields. When mounted on small and inexpensive autonomous underwater vehicles that are programed to traverse a search area, magnetometers provide a means to create magnetic maps that can be used to locate buried minerals. However, to produce useful maps, significant corrections are required to remove the magnetic footprint of the vehicle - the vehicle heading and the vehicle thrusters create fluctuations in the local field that dominate the signal emmitted by local buried features. In 2016, Ocean Floor Geophysics (OFG) successfully developed a Self Compensating Magnetometer (SCM) that can be mounted on Autonomous Underwater Vehicles (AUVs). The compensation system uses knowledge of the state of the AUV's thruster, and a semi-empirical model of the thruster's electromagnetic characteristics to estimate the vehicle's complete magnetic footprint in real time and remove it from the measured signal. In order to adapt the SCM for use in other applications, such as locating shipwrecks, unexploded ordinance, pipes or communication cables, the compensation methodology needs to be enhanced for use on Remotely Operated underwater Vehicles (ROVs); ROVs use an arrangement of several thrusters to move equally well in surge, sway, heave and yaw (unlike an AUV which uses a single thruster to generate surge motion). To modify the OFG SCM correction algorithm so that it can be applied to multi-thruster electric ROVs, a model of the total thruster induced magnetic field must be be derived. This model can be used to determine the structure of the correction equations, and to design a calibration maneuver and optimisation algorithm to automatically determine the coefficients of the compensation equations. In the current project, the modeling, calibration and optimization procedures are being developed and field tested using a small Saab-Seaeye ROV. When completed, the new SCM system will make it possible for archaeologists, police, port authorities, geologists and oceanographers to perform efficient and useful magnetic surveys of submerged terrain.