Abstract: A remote vapor concentration measurement system comprising a unitary, single-fixed wavelength laser to heat the background surface behind a vapor or gas cloud, the constituents of which are to be detected and measured. A heated background acts as a broad band infrared source for measuring absorption characteristics of the gas or vapor constituents. A spectrally responsive receiver, which for example may be a spectrometer or radiometer having filters at selected wavelengths corresponding to the absorption characteristics of the specie of gas or vapor being detected, is also provided. This receiver measures the relative absorbance of infrared energy at selected wavelengths over a relatively broad infrared range to measure the absorbance characteristics of the specie of gas or vapor of interest. The system also comprises a range finder positioned adjacent the receiver for measuring the distance between the receiver and the background surface along two different paths.