Turbidity is a measure of the cloudiness of water: water with a high silt content (low visibility) has high turbidity. However, describing the behaviour of light as it passes through water is not easily described by a single turbidity value. As light is transmitted through the water it is scattered and absorbed by the particles. Both scattering and absorption reduce the total laser intensity reaching the target surface, and scattering has the added problem of creating false returns at locations other than the target surface itself.
Scattering occurs by the light reflecting in all directions off of the particles in the water. The size of the floating particles has an impact on the scattering characteristics of the light. With many smaller particles in the water the light will scatter relatively uniformly and the scatter pattern will be consistent over time. Fewer but larger particles will scatter light in a more variable manner.
Ultimately, the light transmission characteristics of an environment cannot only be characterized by the turbidity value of the water as size of particle and the makeup of the particles has an impact. For the purposes of demonstrating the performance of the ULS-100 in turbid conditions, a qualitative comparison between the scan quality and image quality is presented.
To understand the impact of silt in the water on the scan quality a number of scans and corresponding pictures were taken with increasing levels of silt in the water. With increasing silt content in the water the quality of the scans degraded. At the point where there is nearly zero visibility in the water it is still possible to obtain some measurement data.