Stray light suppression in FY-2 radiometer with shutter

FY-2 radiometer is a multi-field Ritchey-Chretien（R-C） optical system. Stray light outside the field grazes the secondary mirror, then goes across the primary mirror, and finally hits the detector, which produces the straight hit path. To eliminate this straight hit, we used Tracepro software package to trace the path and used Zemax software package to find out the generation mechanisms of it, and then calculated the area of the straight hit. Based on the simulation and calculation, a shutter with some laminas was designed, which could allow signal light to transmit but prevent the stray light entering into the detector. Results of the simulation illuminate that the direct stray light in this area can be eliminated completely by using the designed shutter. Also the integrated sphere experiment indicates the shutter can decrease 95.2% of the visible stray light.