Laser Absorption Techniques for the Measurementof Atmospheric Water Vapor Concentration

Abstract

A sensitive laser method with fast response time has been developed which is suitable for measuringatmospheric water vapor concentration. The method utilizes the absorption of 33.02 and 27.972 pm radiationfrom a water vapor laser. Experiments were carried out in a 2 m controlled atmosphere absorption cell atconditions corresponding to ground-level to high-altitude atmospheric pressures. Typically, an absorptionof 1% was produced in a 1 m path length by a water vapor pressure of 1.1 Pa at ground level and 2.2 Paat 5 km using 33.02 pm laser radiation. With 27,972 pm laser radiation the absorption is about a factor 50less and can be used when higher concentrations of water vapor are encountered. The response time of thedetecting apparatus can be less than a second and still achieve these sensitivities. Possibilities of building anairborne instrument for measuring water vapor concentration are discussed.