Estimation of underwater horizontal visibility for divers and ROVs

An approximate understanding of horizontal visibility is essential for divers and operators of underwater Remote Operated Vehicles (ROVs). Recently there have been a substantial number of underwater viewing systems which rely on either passive or active imaging and thus require good visibility. In this paper, a practical estimate of the horizontal visibility range for an object is developed using a Single photon avalanche diode (SPAD) camera and Secchi disk (SD). Also, a modified version of the visibility equation is given. Both of these results are from analyzing measurements from a series of indoor and outdoor measurements in sea water. We observe that the horizontal visibility can vary from 0.8x to 1.24x the SD depth values. Thus with a single SD depth measurement, horizontal visibility can be estimated. This can then guide the decision about the appropriate camera mode that can be used in the operation of a ROV at specific location (e.g. seas, lakes, rivers).