A Real-Time Direct Wave Interference Cancellation Method for Underwater Frequency Modulated Electromagnetic Detection System

Underwater active electromagnetic detection has emerged as a prominent technique for underwater exploration. Conventional systems employing narrowband single-frequency transmitting signals exhibit limitations in anti-interference and resolution. To address these constraints, frequency modulated underwater active electromagnetic detection has gained more attention as an advanced solution. But such continuous-wave systems face critical challenges from persistent direct wave interference between the transmitting and receiving antenna upon activation, which severely compromises the detection sensitivity and target identification ability. This paper presents a real-time frequency-modulated direct wave interference leveraging the superposition principle between the original interference and its estimated signal. The amplitude and initial phase of the estimated signal are solved using the Lagrange multiplier optimization. Simulations in this paper demonstrate the proposed method's exceptional performance in canceling sawtooth frequency-modulated direct wave interference. The results show that the proposed method performs excellent in addressing such direct wave interference cancellation issue and achieves a good cancellation rate even at low direct wave interference-to-noise ratios.