New Hyperspectral BRDF Feature of a Table-Top Goniometer in the Diffuser Calibration Lab at NASA GSFC

A Table-Top Goniometer (TTG) was built in the Diffuser Calibration Lab at NASA GSFC to support solar diffuser (SD) calibrations from 350 nm to 2500 nm. So far, it has been used to complete the BRDF calibration for the J1 VIIRS SD witness sample as an effort to validate its pre-launch calibration made by the instrument vendor. The new hyperspectral BRDF feature of TTG was implemented to improve BRDF measurements with high-efficiency and high-spectral resolution, and to simulate on-orbit calibration scenarios. This enables us to figure out the potential difference of BRDF results from measurements using monochromatic and broadband light sources. The preliminary hyperspectral BRDF measurements of spectralon samples were conducted with the appropriate integration time and pixel averaging using a CCD spectrometer from 200 nm to 1100 nm and a UV enhanced broadband laser-driven plasma lamp source. The comparison of BRDF results from the spectrometer and a Si detector is made to validate the new feature. The details of methodology for realization of the hyperspectral BRDF measurement and the BRDF scale transfer algorithm are described. The short-term stability of light source, and uncertainty components are also discussed