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UP: Umweltphysik

UP 18: Atmosph
ärische Spurengase und Aerosole: Instrumentelles

UP 18.4: Fachvortrag

Tuesday, March 14, 2006, 17:15–17:30, E

Search algorithm for optimized line selection in laser absorption spectrometers — •Karl Wunderle, Thomas Fernholz und Volker Ebert — Physikalisch - Chemisches Institut, Universität Heidelberg, INF 253, 69120 Heidelberg, Deutschland

Precise modelling of the atmospheric H₂O/CO₂ budget requires a detailed understanding of the transport processes between atmosphere and phytosphere. To quantify the gas transport of a plant leave we currently develop a tomografic tunable diode laser absorption spectrometer, TDLAS, to realize a non-intrusive spatially and temporally resolved determination of H₂O concentration profiles. To optimize the TDLAS performance, 10⁴ H₂O-lines between λ=1.3−2.9 µ m must be compared with regard to optimal strength, minimized spectral interference and lowest dependence on pressure or temperature variations. Based on the HITRAN04 database and a detailed spectral simulation we developed an automated search algorithm to select the optimal absorption line depending on the experimental configuration and reject all lines with inappropriate absorbance, temperature dependence or spectral interference. Spectral interference by nearby lines is quantified in a pre-selected laser current tuning range by evaluating the standard deviation of the normalized difference between the total spectrum of the modelled setup and the isolated single line spectrum. To optimize the spectrometer performance we additionally calculate the expected Signal/Noise-Ratio, based on the spectrometer configurations as well as published detector data for responsivity, quantum efficiency and D* parameters.