Abstract: A ray split-off and tracing approach is presented to analyze the apparent spectral reflecting performance of a semitransparent fluid layer with undulant surface.For parallel incidence and diffuse incidence of the spectral radiation,the regular ray tracing and the inverse ray tracing are separately employed to realize tracing the ray split-off process.With a clear and simple solving idea, the approach possesses a high calculating rate and small demands for the EMS memory,and is flexible for this kind of problems.The results of the calculating example show the following facts.For diffuse incidence of the spectral radiation,the undulant curve of the surface lowers the reflecting ability of the fluid layer.While for parallel incidence of the spectral radiation,two kinds of different influences on the reflecting ability may be caused by the undulant curve.

Key words: semitransparent fluid, undulant surface, reflecting performance, ray split-off and tracing approach