What is the difference between the blue of the sea and the blue of the sky?

When the weather is clear, there are many tiny dust, water droplets, ice crystals and other substances in the air. When sunlight passes through the air, long-wavelength red light, orange light and yellow light can penetrate the atmosphere and directly hit the ground, while short-wavelength blue light, purple light and indigo light are easily blocked by particles suspended in the air, thus scattering light in all directions and making the sky appear blue. In fact, the scattered blue light is only a small part, and most of the blue light and purple light that have not encountered particles still hit the earth directly, so the white light that hits the earth is still red, orange, yellow, green, blue, indigo and purple. Have you noticed that the sky will become bluer after the heavy rain? The clearer the weather, the bluer the sky. This is because there are a lot of dust particles, water droplets and ice crystals in the air in such weather.

The color of ocean water is determined by the color of reflected light from the sea surface and backscattered light from the sea. Because blue light and green light have the strongest penetrating power in water, there is the greatest chance of backscattering. Therefore, the sea looks blue or green.

Sunlight is projected onto the sea surface, part of it is reflected, and the rest enters the water. When the sun shines vertically on the sea, the reflected light is very small, only about 2% on the calm sea. As the sun approaches the horizon, the reflected sunlight gradually increases. In fact, the amount of sunlight entering the sea varies with many factors, such as the projection angle of the sun, weather conditions, sea surface conditions and the clarity of the sea water. Sunlight is composed of light with different wavelengths, and seawater is selective in absorbing and scattering light with different wavelengths. Sea water absorbs the most red light and transmits the most blue light. Most of the red light can only penetrate the water layer of 2 to 3 meters. Blue light penetrates the deepest, exceeding 500 meters.