ABSTRACT
Water vapor is the most important greenhouse gas, much more effective than CO2. It governs the atmospheric water cycle and is a key component in atmospheric chemistry. The frequent occurrence of phase transitions from vapor to liquid water or ice crystals further enhances the importance of atmospheric humidity. Cloud formation and the various forms of precipitation certainly belong to the most important weather phenomena. Range-dependent differential absorption of laser radiation by water vapor represents a selective and sensitive method for measuring the vertical profile of absolute humidity. In principle, the differential absorption lidar (DIAL) technique is based on comparing the backscattered signals of two laser pulses having slightly different wavelengths. One pulse is emitted on the center of a water vapor absorption line (online wavelength). As the laser pulses propagate through the atmosphere, part of their energy is backscattered to the instrument by particles, typically aerosols or hydrometeors, and by molecules in the atmosphere.
