The influence of uneven temperature distribution on imaging quality of computational ghost imaging (CGI) in the underwater environment is investigated experimentally. It is shown that as the water temperature increases, imaging quality presents a trend from deterioration to improvement. The results can be explained by the changes of the temperature difference between the upper and lower layers of underwater environment and laser spot travelling through the underwater environment. Moreover, the effect from different positions of the underwater environment with the same water temperature on CGI is also discussed.
In an imaging system, resolution and signal-to-noise ratio (SNR) are two important indexes to characterize imaging quality. Ghost imaging is a novel imaging method whose imaging resolution and SNR are affected by the speckle size. In this paper, the relation between speckle size and resolution as well as that between speckle size and SNR in the GI system is analyzed in detail. It is shown that the critical resolution, resolvable minimum-separation between two adjacent objects, is approximately equal to the speckle size (speckle diameter). There exists an optimum SNR when the speckle size is larger than the object size. Based on our conclusion, we propose a scheme to enhance the critical resolution of the GI system by using a vortex beam, and the enhancement ability under different topological charges is clearly presented, which can be quantized by a simple formula.
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