Underwater environment laser ghost imaging based on Walsh speckle patterns

Abstract

Underwater imaging is a challenging task because of the effects of scattering and absorption in water. Ghost imaging (GI) has attracted increasing attention because of its simple structure, long range, and achievability under weak light intensity. In an underwater environment, conventional imaging is limited by low sensitivity, resulting in fuzzy images, while ghost imaging can solve this problem. This study proposes underwater laser ghost imaging based on Walsh speckle patterns. According to the simulated and experimental results, noise resistance and a low sampling rate of ghost imaging based on Walsh speckle patterns are proved. As the turbidity of the underwater environment increases, the imaging quality of ghost imaging based on Walsh speckle patterns decreases. However, it remains much better than that of ghost imaging based on random speckle patterns and Hadamard speckle patterns, whereas conventional imaging is no longer distinguishable. Ghost imaging based on Walsh speckle patterns can be performed with a sampling rate lower than 10%, and the peak signal-to-noise ratio and the structural similarity of the results increase by 150.15% and 396.66%, respectively, compared with random speckle pattern ghost imaging. An identifiable image of ghost imaging based on Walsh speckle patterns can be reconstructed with a sampling rate of 6% in a turbid water environment, which is simulated with the concentration of the milk powder not higher than 11.0 g/L. This method promotes the further development of optical imaging technology for underwater targets with a low sampling rate based on ghost imaging.