Measurement of atmospheric pollution by incoherent optical heterodyne detection

A completely passive pollution detection system using an optical heterodyne receiver with a tunable CO2 laser as the local oscillator is described. The system receives incoherent light from the sun or any object that gives off infrared radiation. The type and quantity of the atmospheric constituents are determined by the measurement of the absorption spectrum specific to the pollutant. Experimental results on the measurement of NH3, SF6, and CCl2F2 are presented, and it is shown that even when several pollutants are combined their individual densities can be accurately measured.