Direct Satellite-to-Underwater Optical Links: A Comprehensive Model

Abstract

Underwater communications are gaining interest in the research community for innovative applications, such as real-time oceanographic data collection, disaster response, underwater exploration, scientific research, marine and defense systems. While optical, acoustic, and radio frequency technologies are being explored, Underwater Optical Wireless Communications (UOWCs) are particularly attractive due to reduced absorption of blue-green light. Indeed, UOWC offers high bandwidth and data rates, and low latency, making it a promising technology in challenging aquatic environments. Direct satellite-to-underwater links could enhance connectivity and command-and-control operations. This paper presents a comprehensive framework for modeling such links and assesses performance under various environmental conditions, taking into account atmospheric transmittance, solar and lunar irradiance, optical properties of the water, backscatter from the water column, surface and bottom reflections, sea foam, and losses at the air-water interface. In particular, the proposed framework considers a layered model for light propagation in water, and includes key system parameters, like satellite position and laser beam footprint. Numerical results demonstrate that it is possible to achieve good performance in the absence of direct sunlight, both in the downlink and uplink directions, and assess the impact of solar reflections, laser divergence and receiver field-of-view. These findings open new possibilities for efficient air-to-underwater communication systems.