I. Introduction
Localization of underwater vehicles or ships is of great importance in both civil and military applications [1], [2], [3], [4]. However, the progress made in the denoising technology for ships has presented significant challenges for acoustic-based methods. As a result, the use of the extremely low-frequency (ELF) electromagnetic field detection technologies has become more prominent. The adoption of these technologies offers several benefits, such as effective concealment and improved target recognition capabilities [5], [6]. Due to the significant attenuation of electromagnetic fields in seawater, the frequency range is limited to the ELF band of 0 to 0.3 kHz. These technologies are used mainly in marine warfare to locate and track moving targets and to activate multiinfluence mines [7]. Generally, the ELF electromagnetic fields include underwater electric potential, corrosion-related magnetic fields, and the shaft-rate field generated by shaft rotation. In this study, we focus on the shaft-rate electromagnetic field, especially the shaft-rate magnetic fields, which has attracted attention from researchers due to its distinct characteristics associated with shaft rotation.