Study on Transmission of Visible Light in Selected Water Bodies of Southwest Nigeria for Underwater Wireless Optical Communication

Abstract

A study on the transmission of visible light (400 nm-800 nm) in some selected natural water bodies of Southwest Nigeria was carried out via spectroscopy, and their salinity, total dissolved solids, and electrical conductivity were obtained. Samples of ten selected water bodies comprising rivers, lagoons, and the Atlantic Ocean were taken namely: River Ala, River Ogbese, River Kinira, River Apake, River Odo-Oru, River Odo-Eran, Epe Lagoon, Lagos Lagoon (Lekki Phase 1), Lagos Lagoon (Victoria Island) and the Atlantic Ocean. The absorption of light in them was measured using a spectrophotometer. From the results of the measurements, the rivers showed less conductivity, total dissolved solids, and salinity compared to the lagoons, and the Atlantic Ocean. The Atlantic Ocean gave the highest value. Also, there is varying optical attenuation with different wavelengths. At shorter wavelengths (blue light), there is higher absorbance with an increase in salinity compared to longer wavelengths (red light). At the infra-red end (750 nm – 800 nm), all the samples showed increased absorbance compared to the absorbance at red wavelength (700 nm). From the measurements, an optical beam of a wavelength of 650 nm was found most suitable for optical communication across these water bodies. The transmission was simulated at this wavelength for the water bodies using OptiSystem software linked with MATLAB at different data rates, and their performance was investigated in terms of received quality factor and bit error rate. The quality factor reduces with an increase in salinity, while the bit error rate increases with an increase in salinity.