Anti-Interference underwater Laser-Spot detection and recognition via temporal correlation enhancement

• M−sequence modulation enables robust underwater laser detection despite interference. • SNR improves from 6.7 dB to 40.5 dB under background light with no synchronization. • Method achieves 43.72 dB SNR under sunlight conditions from initial 4.21 dB baseline. • High-frequency LED interference suppressed from 5.45 dB to 44.5 dB signal quality. • Target spot intensity enhanced 56.25% in turbid water through correlation processing. Underwater optical detection faces complex challenges such as strong background noise interference, sunlight noise and water scattering effects, which significantly reduce the target’s signal-to-noise ratio (SNR) and degrade detection performance. This paper presents a robust underwater laser-spot target recognition and detection method based on spread-spectrum coding and the strong auto-correlation properties of M−sequences, enabling reliable detection under conditions of intense background interference, scattering and low illumination. Experimental results show that by using the proposed method, the raw image’s SNR increased from 6.7 dB to 40.5 dB in the presence of constant high-intensity background light, while still maintaining robust performance at higher background-light power levels. Similarly, under strong sunlight conditions, the SNR increases dramatically from 4.21 dB to 43.72 dB, showcasing the method’s capability to handle sunlight interference. Under interference from a 1 kHz flickering LED, the SNR improves from 5.45 dB to 44.5 dB, demonstrating the method’s effectiveness in suppressing high-frequency flickering noise. In highly turbid water, the method enhances the target spot intensity by 56.25 %, effectively alleviating the masking effects caused by scattering. Furthermore, under low-light conditions with weak illumination, the system achieves an SNR above 45 dB, with a maximum improvement of 38 dB, even at only 46 µW of incident optical power, greatly extending detection range and sensitivity. This approach requires no hardware synchronization between the transmitter and receiver, allowing for reliable and flexible operation. It provides a practical solution for long-range, high-precision localization and recognition, which exhibits significant potential for underwater ranging, positioning and target tracking.