Generalized method for calculating irradiance from black body
The method of calculation of the irradiance produced by a black body in an arbitrary plane parallel to its diaphragm is considered. The method is based on the using of the concept of transmittance of the cold diaphragm of IR FPA, describing the ratio of the radiant flux that hits a given point of the plane through the diaphragm, to the radiant flux, that hits this point from hemisphere. Full convergence of calculation results of the irradiance by the presented method and the only normative method, described in GOST 17772-88, has been established. The calculation results of the irradiances and the normalized irradiance differences from black body with round and square diaphragms in the range 0.06 сm to 20 cm, and the area distribution of irradiance are considered. It is shown that the irradiance from black body with round diaphragm differs from the irradiance from black body with square diaphragm of the same area by no more than one percent. Full applicability of the black body irradiance calculation method has been established.