Abstract: A method and apparatus for remote detection of gas leak and determination of the relative concentration of a gas using nondispersive infrared absorption of backscattered laser light with background compensation. The method includes source of coherent infrared radiation, sealed reference cell, filled with air with admixture of reference gas of known concentration, sealed control cell filled with air, sensitive elements which are sensitive to radiant fluxes in a determined band of wavelengths. The method includes measuring output signals, calculating the difference of the signals from control cell for different points, the difference of signals from reference cell and control cell, the ratio of said differences and relative concentration, and means for converting said concentration into visual image and audio signal.