The noise or thickness of a cloud is a qualitative notion. It is directly related to the accuracy of the distance measure from the scanner.
For example, a scanner that measures a distance with an accuracy(or amplitude) of 1 mm on a surface, creates a cloud of measures with a maximum thickness of 2 mm: Each measure is marred by an error of + / - 1 millimeter, the result is that the surface points measured are not all located at the same distance to 1 millimeter, where the thickness of the cloud when viewed from its edge, from side view.