Narrow-Field Radiometry In A Quasi-Isotropic Atmosphere

If a radiometer having a narrow field of view is used to measure the radiance of a source such as a quasi-isotropic atmosphere, a knowledge of the out-of-field responsivity is critical. For example, if a radiometer with a field of view of 5° (full-angle) has a relative responsivity of 10-4 for the out-of-field radiation, the contribution of the out-of-field radiation (assuming an isotropic source subtending 27 steradians) is 102% of the total signal. Either the stray light suppression of the radiometer must be extremely high or methods of determining the out-of-field response must be developed. A description of one method of determining the effect of out-of-field response and its application to a planetary atmospheric radiometer is presented.