Distance estimations in unknown sea underwater conditions by power LED for robotics swarms

The aim of this paper is to measure distances between autonomous underwater vehicles using power LED as light source and photodiode as receiver in unknown light water adsorption conditions. The method is based on the attenuation of the light signal, depending principally on distance and water characteristics. In a previous paper, we proposed the use of a cheap power LED system to support acoustic devices in localization and configuration computation of an underwater robotics swarm. The idea was based on the exchange of light signals of different wavelengths, to reduce the noise, generated by LEDs; the unknown water conditions, affecting the light propagation, required a local measure of the absorption function a(λ) to obtain the distance between the source and the receiver. To avoid the use of many different wavelength LEDs, we investigated the influence of power and flash duration on the LED spectral emission. Starting from this experience, we are now able to measure distances without the unpractical local measure of the absorption function. In this paper we show as, modifying frequency, we shall be able to measure a(λ) and, consequently, the distance d.