23-27 November 2004CONAE Workshop, Cordoba, Argentina1 Infrared methods for deriving volcanogenic sulphur dioxide Dr Fred Prata 1 Adjunct Professor Michigan Technological University 1 On leave from CSIRO Atmospheric Research, Melbourne, Australia

23-27 November 2004CONAE Workshop, Cordoba, Argentina2 Synopsis of Lecture Remote sensing of SO 2 clouds - basics Some theory Examples of detection - TOVS and MODIS Comparisons and validation New tools - AIRS Questions and Answers

23-27 November 2004CONAE Workshop, Cordoba, Argentina3 SO 2 Budgets Source SO 2 SO 4 Fossil-fuel combustion +industry702.2 Biomass burning Oceans–40–320 Plants+soils–2–4 Volcanoes7–82–4 Units: Tg(S) yr -1 Source: Berresheim et al. (1995)

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23-27 November 2004CONAE Workshop, Cordoba, Argentina8 ~2300 AIRS channels

23-27 November 2004CONAE Workshop, Cordoba, Argentina9 M27M28 M29M30M31M32 M33 ~2300 AIRS channels

23-27 November 2004CONAE Workshop, Cordoba, Argentina10 Ulawun + Plumes can be identified in satellite data using “spectral” discrimination - e.g. MODIS data New Britain, PNG

23-27 November 2004CONAE Workshop, Cordoba, Argentina11 Ulawun µm - 12 µm temperature difference

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23-27 November 2004CONAE Workshop, Cordoba, Argentina13 T IROS O perational V ertical S ounder HIRS instrument with 20 channels ~18x18 km 2 pixels at nadir NOAA satellites Continuous since 1979 Same platform as AVHRR Day/night operation

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23-27 November 2004CONAE Workshop, Cordoba, Argentina15 The Physics of infrared SO 2 sensing Detector IR radiation SO 2 gas ++ absorption emission scattering

23-27 November 2004CONAE Workshop, Cordoba, Argentina16 Satellite (or airborne) detector z a b I

23-27 November 2004CONAE Workshop, Cordoba, Argentina17 Emission from layer modified by SO 2 absorption Emission to space from SO 2 -free atmosphere Emission above SO 2 layer Emission from SO 2 modified by atmosphere

23-27 November 2004CONAE Workshop, Cordoba, Argentina18 Weighting functions for some TOVS channels The weighting function is: ∂t/∂z.

23-27 November 2004CONAE Workshop, Cordoba, Argentina19 Simplifying assumptions 1.We assume that the SO 2 layer lies above the peak of the weighting function for H 2 O in the 7.3 µm channels, so that the absorption coefficient  a (z) is zero for z > a. This is a significant assumption because H 2 O absorbs strongly at 7.3 µm and the weighting function peaks relatively high in the atmosphere. 2.The SO 2 layer is assumed to be isothermal and therefore can be characterized by a single temperature T s. Clearly this assumption is questionable when the SO 2 layer is very deep.

23-27 November 2004CONAE Workshop, Cordoba, Argentina20 The radiance equation can be linearized by expansion in terms of the derivative of the Planck function (∂B/∂T). We denote this as: u*. In terms of measured top-of-atmosphere brightness temperatures we arrive at: Let u = I-I a In practice I, I a are averages over the filter response function of the channel. We write this as u. *

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23-27 November 2004CONAE Workshop, Cordoba, Argentina28 TOVS retrievals

23-27 November 2004CONAE Workshop, Cordoba, Argentina29 SO 2 from TOVS AGU Book Chapman, 2003

23-27 November 2004CONAE Workshop, Cordoba, Argentina30 TOVSTOMS

23-27 November 2004CONAE Workshop, Cordoba, Argentina31 Eruption of Cerro Hudson, southern Chile 7-27 August, 1991

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23-27 November 2004CONAE Workshop, Cordoba, Argentina34 Pinatubo 15 June - 15 July, 1991

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23-27 November 2004CONAE Workshop, Cordoba, Argentina37 Pinatubo SO 2 cloud seen from TOVS - 3 separate instrumnets provide unprecedented temporal resolution

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23-27 November 2004CONAE Workshop, Cordoba, Argentina40 From: Carn, S., Prata, A. J., and Karlsdottir, S. (In prep.)

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23-27 November 2004CONAE Workshop, Cordoba, Argentina42 SO 2 from AIRS Atmospheric Infrared Sounder (AIRS) New research spectrometer (>2300 channels) EOS- Aqua platform Many new possibilities to study volcanic gases

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23-27 November 2004CONAE Workshop, Cordoba, Argentina44 AIRS Spectra

23-27 November 2004CONAE Workshop, Cordoba, Argentina45 AIRS - volcanic ash 10.7 µm-11.8 µm difference Positive slope =water vapour or cloud

23-27 November 2004CONAE Workshop, Cordoba, Argentina46 AIRS can be used to select optimal ‘broad’ channels for specific applications 11 µm -12 µm 10.6 µm µm

23-27 November 2004CONAE Workshop, Cordoba, Argentina47 AIRS SO 2 for Anatahan 7.3 µm SO 2 feature SO 2 cloud 7.3 µm image Theoretical calculation using Modtran

23-27 November 2004CONAE Workshop, Cordoba, Argentina48 Compared with MODIS

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