Kamau and Yuka are at the beach for a day of exploration and play. The beach they have chosen has unique features such as varying depths due to underwater sandbanks and trenches dug by the tide. As the sun climbs higher, they notice that the light creates a mixture of clearly visible patches on the ocean floor and obscure, darker areas where the sea is deeper. Excited by their findings, Kamau suggests a game of hide and seek. The catch is that the seeker must stand in the water at a fixed depth while looking for the other person, who may be hiding either in the water at a different depth or on the shore.

Kamau goes first as the seeker. He chooses to stand in the water where it reaches just below his waist. Yuka decides to hide by partially submerging herself in a trench that is deeper than where Kamau is standing, with only her head and shoulders visible above the waterline. As the sun is directly above the sea, creating a strong glare on the surface, Kamau finds it challenging to spot Yuka because the light reflects off the water, making it hard to see beneath the surface where Yuka's body is hidden. After a few minutes, frustrated by the sun's reflection, Kamau takes a few steps towards a sandbank where the water is shallower, thinking it might give him a better vantage point. Yuka sees Kamau's movement and decides to move laterally within the trench to remain out of his line of sight.

The question is: how does Kamau's change of depth affect his view, and will this allow him to better spot Yuka? Also, how does Yuka's lateral movement within the trench affect her visibility to Kamau?
The change in Kamau's depth affects his field of vision and perspective in a significant way. When Kamau is standing in the water at waist height, his eyes are closer to the surface of the water, and the angle with which he looks into the water is shallow. This shallow angle of view in combination with the strong glare from the sun makes it difficult for him to see beneath the surface, where Yuka is hiding in the trench.

As he steps onto the sandbank where the water is shallower, the height difference changes the angle at which Kamau is looking into the water. With the water level now lower relative to his eyes - possibly at knee height - his viewing angle becomes steeper. A steeper angle reduces the glare on the water's surface, because the light is not reflecting into his eyes to the same extent. This improvement should theoretically enhance Kamau's ability to see through the water's surface, potentially increasing his chances of spotting Yuka.

However, the change in perspective is not all that is at play here. The clarity of the water and the patterns of light and shadow on the ocean floor also dictate visibility. In clearer patches of water without strong reflections or dappled light, Kamau could potentially see deeper and with greater clarity from his new position. But if the water over the trench remains murky or shadowed, Yuka's lower body would still be obscured.

Yuka's lateral movement within the trench aims to keep her body alignment away from Kamau's line of sight. By moving sideways, she's hoping to either move into a shadowed area where she blends in with the seabed or position herself so that the angle from Kamau's eyes to her position keeps her concealed. Assuming the trench is uniformly deep, her head and shoulders remain the only visible parts above the water. If Kamau's view is straight down the trench, the likelihood of seeing her is higher because he would be looking along the length of it. If she, on the other hand, moves perpendicular to Kamau's line of sight and remains within the shadows, his chances of spotting her decrease because she is likely to blend in with the sea bed or potentially be obscured by any undulating contours of the trench.

Therefore, while Kamau's change in depth does enhance his ability to see underwater by decreasing the glare and providing a more direct line of sight, it does not necessarily guarantee he will spot Yuka. She can reduce her visibility further by moving laterally into areas where the natural light or seabed features help camouflage her.