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UP: Fachverband Umweltphysik

UP 8: Methods 1

UP 8.2: Vortrag

Mittwoch, 28. März 2012, 17:45–18:00, HFT-FT 131

How accurately can we calibrate an SO₂ camera? — •Peter Lübcke, Nicole Bobrowski, Sebastian Illing, Leif Vogel, and Ulrich Platt — Institut für Umweltphysik, Im Neuenheimer Feld 229, 69120 Heidelberg

SO₂ fluxes start to be monitored at a considerable number of volcanoes for volcanic risk assessment. The SO₂ camera, based on a 2-D UV sensitive CCD and two band-pass interference filters, is an instrument for remote sensing of volcanic emissions based on measuring the ultra-violet absorption of SO₂ in a narrow wavelength window around 310 nm. A second wavelength interval around 330 nm is used to correct for broad band absorption effects and Mie scattering. To obtain correct SO₂ fluxes that can be compared to other measurement techniques and used for volcanological models, it is important to calibrate the SO₂ camera carefully. Today, the most common approach for calibration is measurements using calibration cells of known concentration, neglecting effects that can occur due to aerosols (e.g., ash) in the volcanic plume. We present results from a case study at Popocateptl, Mexico, 2011, where we calibrated the SO₂ camera with a coaxial Differential Optical Absorption Spectroscopy (DOAS) system. We compare the calibration cell approach to the DOAS calibration method and verify the respective results with measurements from an Imaging Differential Optical Absorption Spectroscopy System (IDOAS). We will discuss the general advantages and limitations of an SO₂ camera and under which conditions the calibration cell method might fail and possibly lead to wrong conclusions about the SO₂ emission flux.