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Volcanic ash and SO 2 retrievals from MODIS and SEVIRI: overview and links to SHIVA project

INGV. Volcanic ash and SO 2 retrievals from MODIS and SEVIRI: overview and links to SHIVA project. S. Corradini and L. Merucci. 26 July 2013 – Oxford – SHIVA Meeting. 1. 1. Overview. Ash and SO 2 retrieval from multispectral data in the TIR spectral range Error Assessment

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Volcanic ash and SO 2 retrievals from MODIS and SEVIRI: overview and links to SHIVA project

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  1. INGV Volcanic ash and SO2 retrievals from MODIS and SEVIRI: overview and links to SHIVA project S. Corradini and L. Merucci 26 July 2013 – Oxford – SHIVA Meeting 1 1

  2. Overview • Ash and SO2 retrieval from multispectral data in the TIR spectral range • Error Assessment • Atmospheric and Surface Parameters • Ash Optical properties • Water/Ice plume retrievals and SO2 correction • Conclusions and Contribute to the SHIVA project 2

  3. Overview • Ash and SO2 retrieval from multispectral data in the TIR spectral range • Error Assessment • Atmospheric and Surface Parameters • Ash Optical properties • Water/Ice plume retrievals and SO2 correction • Conclusions and Contribute to the SHIVA project 3

  4. BTD < 0 volcanic ash The cloud discrimination is based on Brightness Temperature Difference algorithm [Prata et al., GRL,1989](+ water vapor correction [Prata and Grant, CSIRO, 2001; Corradini et al., JARS, 2008]) BTD = Tb(11m) - Tb(12m) BTD > 0 meteo clouds The ash retrievals are based on computing the simulated inverted arches curves “BTD-Tb(11m)” varying the AOD () and the particles effective radius (re) [Wen and Rose, JGR, 1994] re  M(n,m) Ash retrieval in the TIR spectral range

  5. Ash Mass Effective Radius AOD 5

  6. SO2 retrieval in the TIR spectral range  Procedure[Realmuto et al., JGR, 1994; Teggi et al., JGR, 1999] for UTLS plumes 7.3 m 8.6 m for LT plumes Sensor radiance Simulated radiance Ash effect on SO2 retrieval SO2 retrieval • During an eruption generally ash and gases are emitted simultaneously • The plume ash particles reduce the top of atmosphere radiance in the entire TIR spectral range, including the channels used for the SO2 retrieval • The net effect is a significant SO2 overestimation [Corradini et al., AMT, 2008; Kearney and Watson, JGR, 2008] MODIS TIR response functions

  7. MODIS – 24 November 2006 Before correction Total mass = 18728 t After Correction Total mass = 5947t SEVIRI - 12 August 2011

  8. Overview • Ash and SO2 retrieval from multispectral data in the TIR spectral range • Error Assessment • Atmospheric and Surface Parameters • Ash Optical properties • Water/Ice plume retrievals and SO2 correction • Conclusions and Contribute to the SHIVA project 8

  9. Satellite geometry Spectral surface emissivity and temperature Volc. cloud geometry 9 values from 0 to 5, constant step in a log scale P, T, W Ash Optical Properties 21 values from 0 to 10 g/m2, step 0.5 g/m2 8 values from 0.7 to 10 m, constant step in a log scale TOA Radiance computation Radiative Transfer Model The only particles detectable in the TIR spectral range

  10. Ash mass [Corradini et al., 2009] SO2(8.7m) [Corradini et al., 2010 Pugnaghi et al., 2013] Each RTM input parameter has an uncertainty that lead to ash and SO2 retrieval errors % Retrieval Errors 50 40 30 20 10 W Ts  hp tp opt. prop RTM Input parameters (20%) (2K) (3%) (0.5 km) (50%) (type) RTM Parameter Uncertainty

  11. Overview • Ash and SO2 retrieval from multispectral data in the TIR spectral range • Error Assessment • Atmospheric and Surface Parameters • Ash Optical properties • Water/Ice retrievals and SO2 correction • Conclusions and Contribute to the SHIVA project 11

  12. Volcanic Plume Removal (VPR) procedure for the simultaneous retrievals of ash and SO2[Pugnaghi et al., 2013] 1) The plume can be regarded as a region characterised by a dip in the radiance. VPR removes the plume from theimage by linearly interpolating the radiances in the region surrounding the detected volcanic plume, obtaining the radiances that would have been measured by the sensor if the plume was absent 12

  13. 2) The new image and the original data allow computation of plume transmittance in the TIR-MODIS bands 29, 31, and 32 (8.6, 11.0 and 12.0 μm) by applying a simplified model consisting of a uniform plume at a fixed altitude and temperature where 3) To correct the uncertainties of the simplified model considered, the transmittances are then refined with a polynomial relationship obtained by means of MODTRAN simulations adapted for the geographical region, ash type, and atmospheric profiles 4) From the transmittance of the channels centered around 11 and 12 mm: the AOD31,32 depends linearly on the plume AOD550 (with null offset), but with a slope which is a function of the particle size 13

  14. The volcanic cloud altitude and temperature are the only input parameters required to run the procedure Because the effect of the atmosphere and surface is extracted directly by the image (i.e. an ‘ideal‘ correction is realized), the ash and SO2 errors due to the uncertainty of the mentioned parameters are drastically reduced(Pugnaghi et al., in preparation) The estimated overall ash and SO2mass retrieval errors considering W, Ts and  uncertainties of 20%, 2K and 3% respectively, is less than 20% 14

  15. Comparison between VPR and LUT retrievals The SO2 and ash masses and fluxes retrieved from the VPR procedure have been compared with the results obtained by applying the established LUT retrieval approach in 2 case studies. 2006, December 3rd, at 12:10 UTC, MODIS-Aqua low SO2 plume altitude 3.75 km 2011, October 23rd at 21:30 UTC, MODIS-Terra ash and SO2 plume altitude 5.5 km VPR LUT Flux

  16. Overview • Ash and SO2 retrieval from multispectral data in the TIR spectral range • Error Assessment • Atmospheric and Surface Parameters • Ash Optical properties • Water/Ice plume retrievals and SO2 correction • Conclusions and Contribute to the SHIVA project 16

  17. Ash Optical Properties [Tirelli, 2006] Sing. Scatt. Albedo Ext. Coeff Abs. Coeff. Asym. Param. Size Distribution (log-normal Mean=1.7, SD=0.2) Mie Code (spherical approximation)

  18. SO2 retrieval (7.3, 8.7 m) Ash retrieval (11, 12 m) Ash Refractive Index ARIA Database

  19. Flux computation: Ft = mt * ws Plume transects Plume axis AndesiteObsidianPumiceMinDustEyja MODIS Terra Eyja eruption May 10, 2010 22:45 UTC

  20. Ash characterization for the Eyja 2010 eruption phase I: 01 April 2010 phase IIa: 16-21 April 2010 phase IIb: 11 May 2010 O A O A [Borisova et al., JGR, 2012] Andesite-Pollack(1973) Obsidian-Pollack(1973) Pumice-Volz(1973) Mineral Dust-Balkanski(2007) Eyja-Peters(2013) A [courtesy from Taddeucci J. and Misiti V., INGV-Rome] O P M E 20

  21. Linking the IR transmittance to size and type of volcanic ash particles[Scollo et al., JGR submitted] R (mm) ~1250 cm-1 Use of the infrared spectroscopy to investigate the spectral signature of volcanic ash particles. As instrument we used a Bruker Equinox-55 FTIR spectrometer in the range 7000-600 cm-1 (1.43-16.67 μm) to analyse the infrared transmittance of ash particles on KBr windows • Presence of the Christiansen effect (high transmission at a given wavelength in the infrared region) • Decrease of optical depth with decrease of particle radius ( =-ln(T)) • Defining a and b as the distance in optical depth between the minimum and maximum optical depth values with respect to the continuum, the ratio a/b can be compared with the size of the volcanic ash particles. 21

  22. Basaltic Glass R(mm) • Considering the same refractiv index, the peack of the Christiansen effect remain quite constant for different particles effective radii • It vary, varying the refractive index • Andesite is excluded • From the syntetic simulations, the Christiansen peaks are placed at ~1250 and ~ 1359 cm-1 for basaltic glass and obsidian • The basaltic glass refractive index gives the best approximation to the laboratory measurements 22

  23. Overview • Ash and SO2 retrieval from multispectral data in the TIR spectral range • Error Assessment • Atmospheric and Surface Parameters • Ash Optical properties • Water/Ice plume retrievals and SO2 correction • Conclusions and Contribute to the SHIVA project 23

  24. It completely cover the ash signal. These volcanic clouds are indistinguishable from meteorological clouds. Condensed Water Vapour effect on ash and SO2 retrievals Etna 2011 activity: 12 events, from 12 January to 15 November, characterized by ash, SO2 and condensed water vapour emissions 13 January 2011, Catania

  25. WV retrieval and correction and SO2 amount [Corradini et al., in preparation] re t BTD < - 0.2 BTD > 1.5 M(n,m) MODIS 10/04/11 12:30UTC

  26. Before Correction After Correction

  27. Overview • Ash and SO2 retrieval from multispectral data in the TIR spectral range • Error Assessment • Atmospheric and Surface Parameters • Ash Optical properties • Water/Ice plume retrievals and SO2 correction • Conclusions and Contribute to the SHIVA project 27

  28. Our approach for ash and SO2 retrievals is based on a massive use of radiative transfer models • The uncertainties on water vapour profile, surface temperature and surface emissivity is reduced by using the VPR approach [WP3 – Retrieval comparison with other satellite instruments] • The bigger ash and SO2 retrieval errors derive from the uncertainty on ash refractive index [WP1 – Retrieval error sensitivity considering the uncertainty on size distribution, components, etc.] • A procedure, that uses hyperspectral TIR measurements, has been proposed to investigate the volcanic ash composition [WP2 – Ground transmittance analysis] • The volcanic cloud water/ice particles are retrieved and the SO2 abundance corrected [WP3 – Comparison with same retrieval made by IASI] 28

  29. Thanks for the attention 29

  30. MODIS Aqua, 13 May 2010, 13: UTC55 MODIS Aqua, 13 May 2010, 13: UTC55 SO2 Mass (t/km2) Ash = Andesite [IASI: Carboni et al., ACP, 2012 AIRS: Thomas and Prata, ACP, 2011]

  31. Retrieval errors on atmospheric and surface parameters uncertainties for the VPR procedure

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