Diver visibility: why one can not see as far?

摘要

Diver visibility has been one of the key research areas in underwater vision and imaging studies. Its applications also extend into imaging system performance evaluation and prediction, which is important in MIW and ASW operations. These applications are often associated with coastal ocean waters, and this is generally translated directly into turbidity of the water column. While mostly this is the case, exceptions can lead to erroneous predictions and potentially significant consequences. We examine issues associated with such situations, both by model as well as field data, in order to reach better estimates and to explore means to compensate for such effects, to enhance diver visibility. Visibility data collected by Navy divers from clean and relatively calm waters outside Pensacola, during Sept 2001 Gorging Littoral Ocean for Warfighters (GLOW) experiments suggested a closer examination is warranted, as observed diver visibility measured at different spatial frequencies contradicts conventional model predictions. Observation data from two different days, by different divers at different depths were used. The modulation transfer of high frequency components disappears at a level much higher than those predicted by the human vision sensitivity level. Such contradictions can be resolved, once the effect of the turbulence scattering is considered using a general imaging model.