The impact of solar diffuser screen on the radiometric calibration of remote sensing systems

Solar diffusers (SD) are frequently used for the on-orbit calibration of reflective solar bands in space-born remote sensing radiometers. To avoid sensor saturation due to viewing directly reflected sunlight on to the SD while keeping the same optical path and field of view as the scene observations, an attenuation screen, consisting of a two dimensional array of pinholes, is often used in front of the solar diffuser. The screen is either fixed or retractable. The illumination on the SD through the screen pinholes is not uniform due observation geometry and the moving spacecraft platform. We illustrate the effect of the SD screen on the sensor's radiometric calibration by examining the sensor's response variation using actual on-orbit observations taken from the NASA's EOS MODIS. Lessons learned from this analysis will undoubtedly benefit future design and applications.