Define Problems in turbid water - underwater inspection of bridge?

There are three main problems, which limit the viewing performance of an underwater camera. These are:

- Absorption

- Refraction

- Reflection

Absorption reduces the amount of illuminating light that reaches the object from the light source.  It also reduces the amount of light reaching the camera from the object.  This combined absorption of light limits the maximum distance between the camera and the object.  The viewing range is proportional to the power of the light source, and the light sensitivity of the camera used.

The process of refraction causes dispersion of light from the light source across a larger area than would occur in clear water, thus reducing the intensity of the light beam. The light coming back from the subject to camera is also reduced and scattered in a similar fashion causing loss of contrast and image detail in the video signal.

Reflection is probably the most critical factor for the performance of cameras in turbid water. The suspended particles in the path of illuminating light reflect a portion of the illuminating light directly back into the camera.

This backscatter, can often be limiting factor in the use of underwater visual imaging system in turbid water.  The illuminating light reflected back from the suspended particles tends to "swamp" the imaging light from the subject.