Abstract: A radiometric calibration system is proposed to calibrate the sensor array of a space born optical imaging system. The calibration system comprises an occulting plate with an occulting convolution aperture which executes a relative lateral motion with respect to an image of the sun, to effect a deterministic and continuously varying calibration flux level to the sensor array. The shape, size orientation and apodization of the aperture control the functional form of the temporal irradiance function reaching the sensor being calibrated. Continuous calibration functions covering a range from a minimum to a maximum desired flux level are readily achievable.