Basically the layers of air above the water have slight variations (temperature, humidity, pressure) between them in such a way that they each have a small cha

Basically the layers of air above the water have slight variations (temperature, humidity, pressure) between them in such a way that they each have a small change in refractive index that over a distance bends light upwards. Then you have another group of layers of air further up in the 'marine boundary layer' that bends the light back towards the waters surface. This is called an 'atmospheric duct' and is somewhat similar in the effect to a fibre optic cable. Poor mans source: I wrote my thesis 5+ years ago on refractive effects in the maritime boundary layer [1] [1] https://ceed.wa.edu.au/wp-content/uploads/2017/02/DSTO-Refractive-Effects-in-Maritime-Boundary-Layer-Daniel-Betteridge.pdf https://ceed.wa.edu.au/wp-content/uploads/2017/02/DSTO-Refra...