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UP: Umweltphysik
UP 9: Poster: Hydrosph
äre
UP 9.1: Poster
Tuesday, March 14, 2006, 14:00–16:00, C
Imaging concentration profiles of water boundary layer by Double-Dye LIF and inverse modelling — •Achim Falkenroth1 and Bernd Jähne1,2 — 1Institut für Umwelphysik, IUP, Heidelberg — 2Interdisziplinäres Zentrum f. Wissenschaftl. Rechnen, IWR, Heidelberg
Laser-Induced Fluorescence (LIF) is applied to observe directly the mechanism of gas exchange in the aqueous viscous boundary layer.
In order to make dissolved oxygen visible, a new class of fluorescent dyes is used with a life time in the order of microseconds, so that the quenching constant for dissolved oxygen is sufficiently high for sensitive measurements. Absorption spectra, fluorescent spectra, and the quenching constant are measured.
Depth profiles of the O2 concentration are obtained by two competing techniques. The first technique uses a standard vertical laser sheet and is suitable for a measurement sector up to several centimetres down from the water surface with a resoluion in the order of 50–100 µm.
The second technique uses a second dye that attenuates the emitted fluorescent light differently for different wavelengths so that the shape of the observed fluorescence spectrum depends on the path length of the light in the water. For a given wavelength, the fluorescence received is the integrated intensity over a characteristic depth ẑ = α−1(λ), where α(λ) is the absorption coefficient of the dye solution. Because α(λ) is known, the depth-dependent concentration can be computed from the spectra as a linear inverse problem.
This technique is specially useful for water surfaces undulated by waves, because it results in a coordinate system fixed to the water surface.