Accuracy and precision of laser spectrometers for trace gas sensing in the presence of optical fringes and atmospheric turbulence

Year: 2011

Authors: Werle P.

Autors Affiliation: Karlsruhe Institute of Technology KIT, Institute of Meteorology and Climate Research IMK-IFU, Kreuzeckbahnstrasse 19, Garmisch-Partenkirchen 82467, Germany

Abstract: Spectroscopic techniques are increasingly used for field laser applications in industry and research. Under field conditions complex gas sensors cannot be considered as stable and therefore drift characterization is a key issue to distinguish between sample data and sensor drift. In this paper the history of von Neumann\’s two-sample variance and Allan variance stability investigations in the field of frequency metrology and the relationship to wavelet analysis are reviewed. The concept has been used to characterize accuracy and precision of spectroscopic data in the time domain and practical guidelines for the interpretation of s/t plots are presented. Two topics relevant for spectroscopic measurements are discussed: First, the optical fringe effect, which is present in any spectrometer, limits the precision and accuracy of spectroscopic measurements by forming time dependent background structures superimposed to the signal under investigation. The two-sample variance is used to characterize optical etalons and long-term drift using s/t plots. Second, the short-term instrument stability characteristic in the presence of atmospheric turbulence is discussed. This is important for laser-based gas monitors measuring the turbulent transport of trace gases between the biosphere and the atmosphere using the eddy-covariance technique. It will be shown how the spectral characteristics of turbulence in the Kolmogorov inertial subrange can be identified in the time domain and how the effect of optical fringes can be separated from atmospheric signals.

Journal/Review: APPLIED PHYSICS B-LASERS AND OPTICS

Volume: 102 (2)      Pages from: 313  to: 329

KeyWords: Accuracy and precision; Allan variance; Drift characterization; Eddy covariance technique; Field conditions; Frequency metrology; Gas monitor; Gas sensors; Inertial subrange; Key issues; Kolmogorov; Laser spectrometers; Long term drift; Optical etalons; Optical fringes; Practical guidelines; Sample data; Sample variance; Sensor drift; Spectral characteristics; Spectroscopic data; Spectroscopic measurements; Spectroscopic technique; Time dependent; Time domain; Trace-gas sensing; Trace-gases; Turbulent transports, Atmospheric thermodynamics; Etalons; Gas detectors; Laser applications; Sensors; Spectrometers; Spectrometry; Time domain analysis; Wavelet analysis, Atmospheric turbulence
DOI: 10.1007/s00340-010-4165-9

Citations: 159
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