Patent ID: 7880156

Claim:
A method, comprising: simultaneously illuminating a common area of a sheet of paper using multiple first radiances, the first radiances illuminating the sheet from different directions, each first radiance having a wavelength or wavelength band; measuring multiple second radiances from the sheet, each second radiance including at least a portion of two or more first radiances that have interacted with the sheet; and determining an internal structure of the sheet by determining a scattering profile based on the measurements of the second radiances; wherein no wavelength that is included in the second radiances and that is measured and used to determine the internal structure of the sheet illuminates the common area of the sheet from more than one direction; and wherein the determined internal structure of the sheet comprises at least one of: a location of an internal boundary within the sheet between two layers identified by a discontinuity in the scattering profile; and a non-uniform distribution of a filler in the sheet identified by a smooth variation in the scattering profile.