Long Range and Long Duration Underwater Localization Using Molecular Messaging

In this paper, we tackle the problem of how to locate a single entity with an unknown location in a vast underwater search space. In under-water channels, traditional wave-based signals suffer from rapid distance- and time-dependent energy attenuation, leading to expensive and lengthy search missions. In view of this, we investigate two molecular messaging methods for location discovery: 1) a Rosenbrock gradient ascent algorithm and 2) a chemical encoding messaging method. In absence of explicit diffusion channel knowledge and in presence of diffusion noise, the Rosenbrock method is adapted to account for the blind search process and allow the robot to recover in areas of zero gradient. The two chemical methods are found to offer attractive performance trade-offs in complexity and robustness. Compared to conventional acoustic signals, the chemical methods proposed offers significantly longer propagation distance (1000 km) and longer signal persistence duration (months).