An extension to proposed possibilities for calibrating optical imaging instruments in space

The O'Mongain et al. (1983) study of possible methods for the calibration of optical imaging instruments in space has recommended a diffuser, placed in front of the instrument's primary optics, under solar illumination. Monitoring is conducted by alternately viewing the diffuser and the sun. With certain instrument configurations and dimensions, however, it may not be technically feasible to present such a diffuser to the primary optics and to remove it during normal measurement. A method is proposed in which the instantaneous radiance of a pixel is the same as the radiance of that pixel, averaged over time, which is needed by the scanner in question to survey the entire target area. Attention is given to the technical and operational difficulties that must be overcome in order to implement such a method.