Zwei-Farbstoff-Technik zur Tiefenrekonstruktion von Gaskonzentrationen in der wasserseitigen Grenzschicht

In the present work a laser-induced fluoerscence (LIF) technique for visualizing 3 dimensional gas profiles in water was further developed. This technique allows studies of small-scale processes in the aqueous boundary layer and, since the fluorescence intensity depends linearly on the pH value, it takes advantage of the acid/base reaction of the used fluorescence indicator. Thus gases, which change the pH value, can be traced by using such an indicator. A second, absorbing but non-fluorescent dye causes non-linear changes in the measured spectra, which depend on the travelled distance in the solution. The key idea for this approach was taken from differential optical absorptions spectroscopy (DOAS), in which atmospheric trace gas concentrations are determined by measured absoption spectra. The major goal was finding and analysing suitable dyes. In order to be able to use the LIF technique for gas profile measurements, the dyes needed to meet certain criteria. Various dyes were thoroughly examined and in the course of this work three suitable absorber could be determined. An illumination method for 3 dimensional depth reconstruction was designed, in which the laserbeam was expanded by an optical system and the resulting homogeneous patch was projeced onto the water surface. This illumination method allowed scale analysis of patterns caused by CO2 concentration fluctuations.