1. "Validation of TOMS Volcanic Aerosol and SO2 Products Using MODIS and AVHRR"


2. Progress Report - June, 2002


3. Principal Investigator: Gregg J.S. Bluth


4. Period Covered: 7/1/01 - 6/30/02


5. Institution Address:


Department of Geological Engineering and Sciences

Michigan Technological University

Houghton, MI 49931


6. NASA SENH Grant NAG5-11062


Project Overview (from original proposal)

This proposed research stems from the unique capability of our research group to validate the TOMS SO2 and aerosol retrievals from other (infrared) satellite-based instruments, previously with AVHRR and GOES and now with Terra's MODIS sensor. We believe we are in position to provide the Earth Enterprise project with a valuable validation capability and complementary data products for the study of volcanogenic sulfur dioxide and aerosols.


The goal of this project is to provide a better understanding of the formation and fate of volcanogenic tropospheric aerosols, through improved detection, accuracy and interpretations of TOMS data. We will focus on several objectives to accomplish our goal: (1) using the recent eruption of Hekla (and for other eruptions) derive SO2, ash and aerosol products from MODIS and other infrared satellite data to compare with TOMS measurements; (2) use the TOMS 20-year database and wind trajectory modeling to analyze cases of ash, aerosol and gas separation in drifting clouds, in order to compare IR/UV satellite retrievals; and (3) quantify chemical reaction rates for sulfur dioxide removal, and aerosol formation and removal, under a broad range of volcano-atmosphere conditions.

Research Progress, 7/01 - 6/02 (see Tables 1 and 2)


The progress on our proposed first year tasks is as follows:


¨Hekla case study. The Hekla 2000 eruption is being studied with TOMS, MODIS and AVHRR sensors. We have completed the analysis of cloud retrievals of TOMS and AVHRR and are in the midst of the MODIS evaluations. The SO2 work on MODIS is taking longest as we are perfecting algorithms and working on two separate retrieval methods. We are expecting to complete all data analysis this summer and write up the final manuscript by fall (Rose et al., 2002 - Table 1). The eruption is important because it is an ash poor stratospheric event which is marked mainly by a cirrus cloud which has a high SO2 content.

¨MODIS-TOMS retrieval comparisons. Several projects are well underway. The basic IR retrieval methodology has been established and documented, and forms the basis of two publications by Watson et al. (Table 1). We have written an aerosol forward model and embedded it in a model atmosphere. The aerosol forward model is based upon freely available MIE scattering code that calculates extinction efficiency factors for an aerosol of known refractive index and size. The model atmosphere is a three-level, MODTRAN-based absorptive atmosphere through which radiation is iteratively passed. The complete forward model allows us to model the effects of changes in the atmosphere upon our aerosol retrievals and perform sensitivity analyses of current retrieval methodologies, such as the "split window" retrieval used with AVHRR.

The February 6, 2001 eruption of Nyamuragira volcano (Democratic Republic of Congo) has been observed by both TOMS and MODIS. This is a key eruption for methodology study because it involves a tropical (wet) atmosphere. Work to date has included sensitivity studies of the MODIS retrievals to inputs (cloud thickness, height, ground elevation, and background emissivity). TOMS and MODIS SO2 data are resampled to identical resolutions for comparison, and show overall agreement but numerous differences which appear to be due to atmopsheric water vapor interferences (Bluth et al., 2002 - Table 1).

¨Identification of eruptions in TOMS database for species separation. The initial study has been completed, with all VEI 3 and above eruptions in the TOMS database examined for evidence of gas and ash species separation over the course of at least two days. Thirty-nine eruptions of VEI 3 and above have been identified in the TOMS database as suitable for study (i.e., have observable ash and gas clouds). Of these, 74% show significant separation; 20% show possible/slight separation, and 6% (2) show no evidence of separation. The apparent timing of the separation has been documented, although is subject to significant uncertainty owing to the TOMS daily imagery. 92% of observed separation has been identified during the first day of TOMS data. The timing is critical to an understanding of possible mechanisms of separation, with respect to pre-eruption conditions versus post-emplacement separation (e.g., gravitational settling) (in Carn et al., 2002 - Table 1).



Personnel Update

Two graduate students have been recruited to work on this project. Yingxin Gu completed a Master's degree (co-advised by Bluth), and started a Ph.D. in Spring 2002. Although she is supporting this project, she currently has outside support and will receive support from this project beginning Fall 2002. Emily McCarthy has been recruited from this year's group of applicants to work on this project, starting Fall 2002. Two other graduate students, Jeremy Shannon and Lizzette Rodriguez, are working on related studies of sulfur reactions and removal rates. These two students are funded by Department of Education Fellowships.

Two undergraduate students have been working on related tasks, although both have since secured outside funding to support their work and travel. Alexandria Guth has focused on the numerous Nyamuragira eruptions, and has catalogued over 150 days of TOMS-observed emissions. Shannon Kobs has been searching the TOMS database for cases of observed ash-gas separation, and documenting the degree and timing of the separation.


Table 1. Manuscripts Related to This Project, 7/01 - present

Bluth, G.J.S., I.M. Watson, W.I. Rose, S. A. Carn, A.J. Krueger, V.J. Realmuto, and L.R. Lait (2002, in prep.) Multispectral Retrievals of Sulfur and Ash Emissions from Nyamuragira Volcano. For submission to Special Issue of Journal of Volcanology and Geothermal Research "Volcanic Observations from Space", M. Ramsey and L. Flynn, eds.

Carn, S.A., A.J. Krueger, G.J.S. Bluth, S.J. Schaefer, N.A. Krotkov, I.M. Watson, and S. Datta (2002, in review) Volcanic eruption detection by the Total Ozone Mapping Spectrometer (TOMS) instruments: a 22-year record of sulfur dioxide and ash emissions. In: C. Oppenheimer, J. Barclay & D. Pyle (eds.), Volcanic Degassing, Special Publication of the Geological Society of London.

Rose, W.I., G.J.S. Bluth, I.M. Watson, T. Yu, Y. Gu and A.F. Prata (2002, in prep.) Hekla's February 26, 2000 Eruption as seen and Measured from Space using MODIS, TOMS and AVHRR. For submission to Special Issue of Journal of Volcanology and Geothermal Research "Volcanic Observations from Space", M. Ramsey and L. Flynn, eds.

Watson, I.M., V.J. Realmuto, W.I. Rose, A.F. Prata, G.S.J. Bluth, T. Yu (2002, in prep.) Thermal Infrared Remote Sensing of Volcanic Emissions Using the Moderate Resolution Imaging Spectroradiometer (MODIS). For submission to Journal of Volcanology and Geothermal Research

Watson, I.M., V.J. Realmuto, W.I. Rose, G.S.J. Bluth (2002, in prep.) Forward Modeling of Volcanic Cloud Transmissions Within Different Atmospheres. For submission to Journal of Geophysical Research - Atmospheres.


Table 2. Presentations Related to This Project, 7/01 - present

Bluth, G.J.S., I.M. Watson, W.I. Rose, V.J. Realmuto, S. Carn, A.J. Krueger and L.R. Lait (2001) MODIS and TOMS retrievals of volcanic sulfur and ash emissions from Nyamuragira volcano. Eos Transactions AGU, 82, F1361-F1362.

Carn, S.A., D.J. Schneider, G.J.S. Bluth, W.I. Rose, S.E Kobs (2002) On the separation of ash and sulfur dioxide in volcanic clouds. Spring AGU meeting, Washington, D.C.

Carn, S.A., A.J. Krueger, G.J. Bluth, S.J. Schaefer, N.A. Krotkov and S. Datta (2001) Ultraviolet remote sensing of volcanic emissions: current capabilities and future prospects. Origins, Emissions and Impacts of Volcanic Gases, The Geological Society, October 25-26, London, England.

Guth, A.L., G.J.S. Bluth and S.A. Carn (2002) Analyzing sulfur dioxide emissions of Nyamuragira volcano. Spring AGU meeting, Washington, D.C.

Rose, W.I., G.J.S. Bluth, I.M. Watson, T. Yu, and Y. Gu (2001) Hekla's February 26, 2000 eruption as seen and measured from space using MODIS, TOMS and AVHRR. Eos Transactions AGU, 82, F1355.

Watson, I.M., V.J. Realmuto, W.I. Rose, G.J.S. Bluth, C. Bader, T. Yu, and Y. Gu (2001) Satellite remote sensing of volcanic clouds using the Moderate Resolution Imaging Spectroradiometer (MODIS). Eos Transactions AGU, 82, F1355-F1356.


Presentations (without published abstract)

Bluth, G. (2001) MODIS and TOMS retrievals of volcanic sulfur and ash emissions from recent volcanic activity. Remote Sensing Institute seminar, October 22, Michigan Tech.

Bluth, G.J.S., I.M. Watson, W.I. Rose, V.J. Realmuto, S. Carn, A.J. Krueger, and L.R. Lait (2001) MODIS and TOMS retrievals of volcanic sulfur and ash emissions from recent volcanic activity. NASA TOMS Science Meeting, November 2-3, Greenbelt, MD.


Research plans for upcoming year (7/02 - 6/03)


Our plans for the second year of funding adhere to our original proposed tasks:


¨MODIS-TOMS retrieval comparisons, as available. We will continue to work on the Hekla and Nyamuragira studies. We also have begun work on the 2001 Cleveland eruption.

¨TOMS database retrievals, as available. Based on the initial work discerning ash/gas separation studies, we will begin detailed studies of the timing of the separation with respect to eruption style, as this information forms the basis for several of the proposed mechanisms for separation (e.g., generated during or post-eruption).

¨Trajectory modeling for 3-D analyses. These will be used as needed in each case study, particularly in the derivation of plume heights and thicknesses for the MODIS SO2 retrievals.

¨Calculation of SO2 decay, sulfate formation and decay rates. This work began in January 2002, and continues with a combination of field (Central America, Montserrat) and remote sensing studies.

¨IR data retrievals. These will coincide with the case studies involving TOMS above.








Dr. G. Bluth, Project PI Date