Performance enhancement of a BSDF test bench using an algorithm fed with laser-tracker measurements

In the field of earth-observation, on-board calibration is often necessary to guarantee the radiometric accuracy of space instruments. A typical method is to use large diffusers in front of the instrument, illuminated with a reference source like the sun [1]. Hence, it is necessary to characterize the scattering properties of the diffuser with excellent accuracy. Given the large size and weight of the diffusers to characterize, CSL have developed a bench which uses a robot arm to manipulate the sample. For the most stringent applications, the typical accuracy of robotic arms is not good enough to measure the BSDF with a satisfactory accuracy. A method have been developed which uses laser tracker measurements of the sample during a calibration phase and compensate for the robot errors. This paper describes the principle of the method and the results obtained. We also present the model of how the orientation error of the sample affects the BSDF relative error.