Variation and sensitivity in spectral thermal IR emissivity measurements

Changes of spectra due to changes of variations in the physical features of the surface and view angle can impact the processing and exploitation of thermal IR hyperspectral images and need to be understood. To help accomplish this, FTIR spectrometer measurements were made on a set of known targets over a period of three days in order to assess the precision and repeatability of thermal IR spectral emissivity measurements of the effects of view direction and surface roughness. These measurements are intended to provide validation data for the model and advance our capability to make precise measurements of emissivity in the field. Two types of rock targets, each with three roughness classes and at three view nadir angles were measured over three consecutive days. The results within days were very consistent. Emissivity for the 60 degree view was shifted downward: a sensitivity analysis was conducted to explain this and other variations and is discussed in this paper. The spectra for the large rock size class tended to be lower than targets with smaller rocks. Preliminary modeling results will be presented.