Experimental Study on Optical Imaging of Convex Mode-2 Internal Solitary Waves in Calm Water

The optical imaging mechanism of convex mode-2 internal solitary waves (ISWs) in calm water without wind is investigated based on experimental and simulation calculations. By constructing an optical imaging system in the laboratory, the optical images of ISWs, the matching in situ data, and the free surface displacement caused by ISWs are acquired simultaneously. The experimental outcomes show that the convex mode-2 ISWs exhibit bright-dark stripes in the optical image and produce a depressed free surface displacement on the water surface. The physical model of free surface displacement is constructed in Unigraphics NX (UG) and imported into Light Tools (LTs) for ray tracing. The consistency between simulation calculations and experimental results shows that the free surface displacement generated by the mode-2 ISWs will change the reflection of light, leading to bright-dark stripes in the optical image. A series of experiments were designed to explore the influence of amplitude on the optical imaging of mode-2 ISWs when the thickness of the intermediate layer is different or the same. The results show that the amplitude of the wave will affect the imaging effect of ISWs in the optical image, and the large amplitude will make the stripes clearer in the image.