Odor markers present in natural gas are shown to be useful tracers for imaging of the gas/air mixing progress in technical burner applications. Since tetrahydrothiophene (THT) is commonly used to odor mark natural gas, it is a 'natural' compound present in a wide range of technical combustion systems. The spectroscopic properties of this compound are investigated in static cell experiments giving the background for quantitative interpretation of laser-induced fluorescence (LIF) of THT in isothermal systems. The technique is used to characterize the mixing process of the isothermal and the combusting flow in a technical scale turbulent burner.