Abstract: According to the internal thermal emission of the medium,a new method,pseudo source adding method,is presented to analyze the apparent emissivities of semi-transparent medium layers.By this method,the apparent emissivity formulae are derived for two different cases,in one of which,the semi-transparent emitting surface is considered to be specularly reflecting,and the diffuse reflection is considered in the other.The substrate surface of the layer is supposed to be diffuse and opaque for the two cases.The comparison with the results by the Monte Carlo method is also given.

Key words: semi-transparent medium, apparent emitting property, pseudo source adding method, Monte Carlo method