Optical path structure for open path emissions sensing

The present invention relates generally to remote sensing systems. More particularly, the present invention relates to an apparatus for transmitting, reflecting, and detecting light in an open path sensing system such as a vehicle emission sensing system, having us in detecting and/or measuring one or more components of the air through which the light passes. A gas component analysis system transmits, reflects, and detects light using infrared light source; a reflector unit; and a light detector. The light is transmitted through a gas, such as air containing vehicle emissions, reflected, and detected for analysis and measurement of the amount of absorption that has occurred at known wavelengths. The amount of absorption may be used to determine concentrations of reference gases corresponding to specific wavelengths.