IR LONG-PATH PHOTOMETRY - A REMOTE-SENSING TOOL FOR AUTOMOBILE EMISSIONS

The authors undertook a new approach using an old technology to develop a long-path IR photometer that can remotely measure CO emissions from operating vehicles. The University of Denver's instrument consists of three basic units: the source, a detector, and a computer. IR absorption is used to determine the amounts of CO and CO2 emitted by a passing automobile. The IR light source, located on one side of a roadway, sends a collimated beam into a gas filter radiometer equipped with two liquid-nitrogen-cooled indium antimonide photovoltaic detectors. A 4.3-μm bandpass filter isolates the CO2 spectral region, and a 4.6-μm beam passes through a rotating gas filter wheel one-half of which contains a CO and H2 mixture and the other half N2. The rotating wheel modulates the signal and provides both a reference channel and a CO data channel.