Abstract
In this work, we have investigated the properties of light transport in turbid water for underwater 3D imaging, by comparing literature, simulations, and experiments. The work is motivated by a need for high-quality 3D image data for underwater robotics, also in turbid waters. We present a comparative analysis of how sine wave and line patterns degrade upon propagation through turbid water, and explain the difference in degradation through analysis of the signal response of the water. We find that line patterns provide a sharp signal peak from the un-scattered (ballistic) photons, with a very broad skirt of scattered signal. The detection of the un-scattered peak allows for sub-millimeter 3D reconstruction quality at water turbidities up to 4.8 NTU (nephelometric turbidity units). Using sine waves, 3D precision rapidly drops, as the scattered signal from large parts of the scene causes rapid loss of signal contrast. 3D reconstruction fails at turbidities above 3.1 NTU. In dark parts of the scene, both signal types yield incorrect 3D reconstruction, as forward scattered signal from surrounding brighter regions dominate over the correct signal peak. In line with literature on scattering properties of water, we find that the use of long wavelengths (red signal) gives less scattering and higher signal contrast compared with the use of green and blue, thereby providing lower 3D noise.