Setup for studying speckle noise of spectroradiometer diffusers in Earth observation applications

Diffusers in in-orbit spectroradiometers cause speckle under partially coherent solar radiation. A speckle pattern entering a spectroradiometer through a small slit creates systematic spectral deviations in measured spectra. We have developed a setup to characterise the spatial speckle of diffusers and the related spectral features. The decorrelation angles measured at 532 nm for Spectralon, Diffusil, and Heraeus diffusers were 0.021°, 0.014°, and 0.005° respectively. This information can be used for compensating speckle-related spectral features from the radiometric satellite measurements by averaging over multiple decorrelated spectra. (paper)