The Color of Water

On Day 4 of the Expedition, I was fortunate enough to witness the retraction of the JR’s VIT (vibration isolated television, or underwater camera) through the glorious blue glow of the moon pool.  At first I wondered why the water appeared such a vibrant blue, until I thought about the properties of water and what was actually happening to the light.  The appearance of water depends on the scattering of white light and H2O’s absorption of wavelengths of red light; therefore the farther light must travel through water to reach our eyes, the bluer the water appears.  The light that illuminates the moon pool must first travel the draught of the ship (~7 meters), then over to the center of the beam of the ship (~10 meters), and finally up through the moon pool (an additional 7 meters).  This length of travel and refraction means virtually all the of the red wavelengths of light have been absorbed by water, leaving the moon pool to glow a brilliant, pure blue.