On-orbit radiometric calibration using a solar diffuser

Radiometric calibration of spacecraft sensors using an on-board diffuser has become an accepted method in recent years for sensors operating in the solar-reflective portion of the spectrum. In many of these approaches, the radiance from a sunlit diffuser is used to illuminate the full aperture and full optical path of the sensor. If both the bi-directional reflectance distribution function (BRDF) of the diffuser and the incident solar irradiance are known, the absolute radiance from the diffuser can be used to determine the absolute radiometric calibration of the sensor. In this work, a method for the absolute radiometric calibration using a diffuser made of S13G/LO paint for a silicon-based detector sensor with spectral bands similar to Landsat-7 ETM+ is discussed. The spectral BRDF of a witness sample of the diffuser was measured with the goniometric facility at the Remote Sensing Group of the Optical Sciences Center at the University of Arizona. A measured solar spectral irradiance spectra is used to model the radiance at the sensor entrance pupil. Also presented is a sensitivity analysis of the diffuser-leaving radiance as a function of sensor view and incident solar angle. This sensitivity analysis is used to provide an error estimate for the calibration of the sensor using a diffuser based on the S13G/LO paint.