Red light in underwater measurement applications: a short review

In recent years, optical systems operating in the visible spectrum have emerged as the most efficient, low-cost, and environmentally friendly technologies for underwater applications across military, scientific, and economic sectors. While blue and green wavelengths are commonly used due to their lower attenuation in clear water, red light offers distinct advantages in turbid environments. Specifically, red radiation exhibits lower attenuation than blue and green light in such conditions and is non-harmful to marine fauna. This article explores current and potential future optical technologies that utilize red light. Particular attention is given to underwater wireless optical communication systems employing red wavelengths for data transmission in turbid waters. These systems are applicable in underwater wireless sensor networks, communication buoys, and navigation of autonomous underwater vehicles and remotely operated vehicles. Additionally, the use of red light in underwater photography is discussed, along with two systems designed for fish counting in aquaculture and for monitoring marine fauna behavior in laboratory settings.