Underwater 3-D Spatial Attenuation Characteristics of Electromagnetic Waves With Omnidirectional Antenna

In this paper, an underwater 3-D spatial attenuation model of electromagnetic waves is proposed to establish a position recognition system in underwater 3-D space using distance estimation. The distance estimation is based on signal attenuation characteristics of electromagnetic waves radiated through several omnidirectional antennas. Positions in underwater environments have been predominantly estimated by an ultrasonic position recognition system using travel time and phase difference. However, such a system provides inaccurate estimation on account of the multipath effect in a structured environment or complex environment with many obstacles. A position estimation method that uses signal attenuation of electromagnetic waves has been proposed to overcome this limitation. That method can precisely estimate position on a structured 2-D plane. In this paper, an existing underwater position estimation system based on electromagnetic waves is expanded into 3-D space using the Friis formula and plane wave equation, thereby classifying attenuation characteristics of electromagnetic waves into the effects of medium, radiation, and antenna. These effects are summarized to deduce the signal attenuation characteristics of electromagnetic waves in 3-D space. In addition, the relative position (R, Θ, Φ) and attitude (φ,θ, ψ) of transceiver antennas are used to define a coordinate system for 3-D estimation; moreover, an attenuation model is defined for individual factors in the coordinate system. A generalized attenuation model of an omnidirectional antenna in 3-D space is presented, and the validity of the proposed model is demonstrated through experiments. Based on the results, the proposed model demonstrates the potential application to an omnidirectional antenna and expansion into an attenuation model based on the 3-D position between random antennas.