Embodiments disclosed herein relate to a thermal processing chamber having a substrate monitoring system. In one embodiment, a temperature monitoring system is disclosed herein. The temperature monitoring system includes a housing and a window defining an interior volume. The temperature monitoring system further includes two or more light sources, a camera, and a polarizer. The two or more light sources are disposed in the interior volume, beneath the window. A first light source of the two or more light sources has a first wavelength. A second light source of the two or more light sources has a second wavelength. A camera is disposed opposite the two or more light sources. The camera to captures a plurality of frames of two or more light beams received from the two or more light sources. The polarizer disposed in an optical path of the two or more light beams.