Two-dimensional thickness distribution measurement using near infrared spectroscopy

We report on the development of a measuring method based on near infrared (NIR) spectroscopy, which is able to determine the thickness as well as the homogeneity of polyurethane lacquer coatings in two dimensions in the field of wind turbine blades. The typical thicknesses of these polyurethane lacquer coatings (50-350 mu m) were investigated. NIR spectra were recorded in reflection mode. Quantitative analysis of the spectral data was carried out with partial least squares regression. Measurements were performed on a scanning device developed in-house at scanning speeds up to 0.05 m(2) s(-1). It was shown that quantitative data with excellent precision (standard derivation below 10%) can be obtained.