Estimating deep water radiance in shallow water : adapting optical bathymetry modelling to shallow river environments

The effect of deep-water radiance on modelling bathymetry in shallow rivers using Lyzenga's algorithm was investigated.To this end, a new method for estimating deep-water radiance in the absence of deep water is presented.This parameter is necessary for applying Lyzenga's optical bathymetry model to aerial photographs and other forms of remotely sensed data.The estimation was tested in the Tana river in northern Finland where the variable in question could be measured as well as estimated, and also in one of the Tana's optically shallow tributaries, where it was necessary to estimate deep-water radiance.The results show that the estimated values are very similar to measured deep-water radiance values in the larger river, but the effect of deep-water radiance in very shallow water seems to be negligible.The new technique described in this paper allows the Lyzenga optical bathymetry model to be employed in clear-water optically-shallow rivers, where deepwater radiance cannot be measured in the field, which is precisely where Lyzenga's model is able to deliver the highest accuracy.The method also provides a reproducible, unbiased method for estimating deep-water radiance even in water deep enough to digitize it manually from remotely sensed data.