omi science team meeting 24 – 27 june 2008, fmi iterative retrieval of large so 2 from volcanic...

OMI Science Team Meeting 24 – 27 June 2008, FMI

Iterative Retrieval of Large SO2

from Volcanic EruptionsKai Yang1,3, Nikolay Krotkov1,3,

Arlin Krueger2, Simon Carn2

Pawn K. Bhartia3

1GEST, UMBC, Baltimore, MD, USA2JCET, UMBC, Baltimore, MD, USA3GSFC, NASA, Greenbelt, MD, USA

K. Yang, GEST UMBC & GSFC NASA

13th OMI Science Team Meeting, FMI, 24 – 27 June 2008

Detect and Quantify SO2



SO2 Algorithms

Retrieval Challenge:

Wide range of loadings and vertical distributions

Existing Algorithms: Band Residual Difference (BRD) method Linear Fit (LF) method

Both methods are used in making OMI NRT and operational OMSO2 products.

Improvements in addressing these two questions: How small can OMI see? How large can OMI measure?



Profile shapes: O3 (Ω) uses V8 climatology, SO2 (Ξ) uses Gaussian specified by a central height and a width.

Initial guess: latitude based O3 guess or an adjacent pixel O3 value, no SO2, derive MLER cloud fraction (Fc) at λ=333 nm, using OMCLDRR cloud pressure.

Iterative Spectral Fitting (ISF) Method:

Combo O3 and SO2 Retrievals

tttt

cc

iN

iic

tt

obs

FFF

IcF

IIII

11

0

0

2

1

RRS

,

ln

Ringlnln

lnln



Sample Results:Eruption of Sierra Negra

10/22/200510/22/2005

10/23/200510/23/2005



Sierra Negra Eruption 10/23/2005OMI Retrievals: ISF vs. LF

ISF SO2 Mass LF SO2 Mass 1740 kilotons 950 kilotons (-45%)



Largest SO2 Pixel Value

Orange: lava flowsAqua MODIS Bands 7, 2, 1 Composite



Ozone Consistency:Inside and Outside of the Plume

Along track plots of O3 and SO2

(Along track)



Ozone Consistency:Inside and Outside of the Plume

Maps of O3: ISF vs. LF



How Good are ISF Retrievals?High SO2 Fitting Residuals

1 N-value = -2.3% Radiance

Window = 317.85–333.00 nmError = 0.58 %



High Precision Fitting

Medium SO2 Low SO2

Fitting Error = 0.25% Fitting Error = 0.15%

Background SO2

Fitting Error = 0.14%



SO2 Vertical Distribution

Assumed profile too lowImeas<Iassum at short λ

Simulated Retrievals

Assumed profile too highImeas>Iassum at short λ



Improving Retrieval Accuracy:Adjusting SO2 Central Height



Comparison with AIRS SO2

SO2 central height



Anatahan Eruption: 04/06/05 Iterative Spectral Fit Linear Fit: OMSO2 TRMDerived SO2 central height ≈ 10.5 KM Assumed Central height = 7. 5 KM



Anatahan Eruption: 04/06/05OMI – AIRS Comparison

Iterative Spectral Fit AIRS BTΔ



Anatahan Eruption: 04/06/05Aerosol Index

Iterative Spectral Fit OMTO3

Linear Fit, OMSO2 Terra MODIS



Nyamuragira Eruption:11/28/06SO2 & Aerosol Index

ISF SO2 ISF AI

OMTO3 AI OMSO2 AI



Height & Distance

Nyamuragira, DR CongoNov 28 – Dec 04, 2006SO2 Plume height ~ 7 KM

Sierra Negra, Galápagos IslandsOct 23 – Nov 01, 2005SO2 Plume height ~ 3 KM



Height & Distance

Soufriere Hills, Montserrat, West IndiesMay 20 – June 11, 2006SO2 Plume height ~ 13 KM on May 20Distance tracked ~ 20000 KM



Summary

Operational OMSO2 products tend to underestimate SO2 column amounts, more so when they are large ( > 50 DU).

New algorithm provides more consistent ozone values inside and outside of volcanic plumes, and more precise SO2 columns. Record SO2 column retrieved.

OMI UV2 measurements contain SO2 vertical distribution info. Derived central plume heights are consistent with near simultaneous AIRS observations.

The slope of theFc-λ curve yielded from the fitting algorithm may be used as a better aerosol index.

omi science team meeting 24 – 27 june 2008, fmi iterative retrieval of large so 2 from volcanic...

Documents