The optical characteristics of paper are a function of moisture content. The relation of moisture content and optical properties of paper has been characterized using a microscopic method. This represents a novel technique for moisture measurement with a high spatiotemporal resolution. The uncertainty in the moisture content measured optically was found to be 1.5%.
Moisture content of a paper sample during a wetting experiment is shown in the Figure. Water is introduced from the top and wets the sample around the black cut out section. (Field of view: 7 mm by 16 mm)