Bathymetric mapping will be most straightforward where water quality and atmospheric conditions are invariant over the scene. Under these conditions, both depth and an effective attenuation coefficient of the water over several different bottom types may be retrieved from passive, multispectral imagery. As scenes become more complex-with changing water type and variable atmospheric conditions-it is probable that a strictly spectral analysis will no longer be sufficient to extract depth from multispectral imagery. In these cases an independent source of information will be required. The most likely sources for such information are spatial and temporal variations in image data.