Download Validation of OMI L2 Sulfur Dioxide retrievals over volcanic

NASA NRA NNH04ZYS004N
Measurements, Modeling and Analyses in Support of Aura and Other NASA Satellite
Observations of the Earth’s Atmosphere
Validation of OMI L2 Sulfur Dioxide retrievals over volcanic and
anthropogenic sources
Progress Report – FY2012-2013
PI:
S. A. Carn
Department of Geological and Mining Engineering and Sciences, Michigan
Technological University (MTU), Houghton, MI 49931, USA
Collaborators:
N. A. Krotkov, K. Yang
Code 614, NASA Goddard Space Flight Center, Greenbelt, MD, USA
A. J. Prata
Norwegian Institute for Air Research (NILU), Kjeller, Norway
1. Introduction
The Dutch-Finnish Ozone Monitoring Instrument (OMI), launched in July 2004 on the polarorbiting EOS/Aura satellite, offers unprecedented spatial and spectral resolution, coupled with
global contiguous coverage, for space-based UV measurements of SO2. The OMI SO2 data set is
continuing the NASA Total Ozone Monitoring Instrument (TOMS) record but the improved
sensitivity and smaller footprint of OMI have extended the range of detection to smaller
eruptions, degassing volcanoes, and older clouds, and to anthropogenic pollution. Heavy
anthropogenic emissions and volcanic degassing in lower troposphere and boundary layer
(LT/BL) are now being detected on a daily basis. Using weekly, monthly or annual average SO2
maps we can evaluate longer-term trends, and detect weaker degassing and pollution (e.g.,
http://aura.gsfc.nasa.gov/science/top10_smelters.html). This research focuses on the validation of
OMI SO2 measurements using concurrent satellite data and measurements from sub-orbital
platforms (aircraft, sondes and ground-based instruments). Validation of SO2 vertical column
amounts measured from space is largely opportunistic, owing to the variable spatial distribution
of SO2 and the unpredictable nature of source emissions (particularly from volcanoes). We are
assembling a validation dataset derived from a variety of sources, ranging from dedicated in-situ
sampling of volcanic plumes during the Tropical Composition, Cloud and Climate Coupling
(TC4) campaign in July 2007, to dedicated ground-based validation efforts following the eruption
of Okmok volcano (Alaska) in July 2008, to ground-based and airborne SO2 measurements in
tropospheric volcanic plumes from Redoubt (Alaska) and Turrialba (Costa Rica), to indirect
sources such as electrochemical ozonesondes and UV ozone lidars, and comparisons of nearcoincident satellite SO2 measurements from NASA’s A-Train constellation.
Recent work has focused on comparisons between operational OMI SO2 columns derived
from the linear fit algorithm [Yang et al., 2007] and infrared (IR) SO2 measurements derived from
the Atmospheric Infrared Sounder (AIRS) instrument on the Aqua satellite [Prata and Bernardo,
2007]. Since both Aura and Aqua are flown in NASA’s A-Train polar-orbiting satellite
constellation, OMI and AIRS collect data within ~10 minutes of each other, providing near-
1
coincident SO2 measurements. The only constraint is that, due to interference from water vapor in
the 7.3 µm waveband used to retrieve SO2 column abundance from AIRS measurements, AIRS
usually only detects volcanic SO2 in the upper troposphere and lower stratosphere (UTLS) or
above. We have assembled a list of eruptions detected by both OMI and AIRS in the same ATrain overpass for comparisons (Table 1), using a new technique described below.
2. Volcanic SO2
2.1 Volcanic clouds in the UTLS
In addition to comparing the total SO2 loading in volcanic clouds measured by OMI and AIRS,
we also compare the two datasets in a pixel-by-pixel basis. This is facilitated by the nearcoincident OMI and AIRS measurements in the A-Train, and also by the fact that the OMI and
AIRS footprint sizes are similar (at nadir), being 13×24 km for OMI and ~15×25 km for AIRS
[Prata and Bernardo, 2007]. For the pixel-by-pixel comparisons, we use the following technique.
For each OMI pixel, we find the AIRS pixel with the closest SO2 column amount for increasing
values of the search radius around the OMI pixel center coordinates. Search radii of 0.1º-0.5º in
0.1º increments are used, with a search radius of 0.1º corresponding to essentially collocated OMI
and AIRS pixels, given that 0.1º (≈10 km) is the approximate dimension of a nadir OMI or AIRS
pixel. Despite the near-coincidence of the OMI and AIRS measurements in the A-Train, we
assume that the temporal difference is still sufficient to produce a significant spatial difference in
the measured SO2 columns, particularly for rapidly moving volcanic clouds and/or under high
wind shear conditions.
In due course we aim to analyze all the eruptions listed in Table 1 and fully populate the
Table. Some preliminary results for selected eruptions are shown below. Figure 1 shows the OMI
and AIRS SO2 retrievals for the Jebel al-Tair (Yemen) eruption cloud on October 1, 2007, which
reached an altitude of ~16 km in the UTLS. Both OMI and AIRS measure similar total SO2
loadings of 0.07-0.08 Tg in the volcanic cloud. One can see that the overall SO2 distribution
detected by the two instruments is similar; the main difference is that OMI’s greater sensitivity to
SO2 in the lower troposphere permits detection of low-level SO2 emissions close to the volcano,
which are not detected by AIRS (Fig. 1b). OMI-AIRS pixel correlation plots for the Jebel al-Tair
eruption are shown in Figure 2. For a search radius of 0.1º (Fig. 2a) there is already a reasonable
correlation between OMI and AIRS SO2 columns, though only for near-nadir OMI pixels (nadir =
scan position 30). For off-nadir scan positions there is a significantly weaker correlation between
OMI and AIRS, but this is expected from the increased spatial averaging effect, and possibility of
interference from sub-pixel sized clouds, as the pixel size increases (and the OMI and AIRS pixel
sizes diverge). Increasing the search radius (Figs. 2b-e) leads to a very robust correlation between
OMI and AIRS SO2 columns, indicating that the two instruments measured similar column
amounts in the same broad region of the volcanic cloud.
Figures 3 and 4 show analyses of the April 2005 eruption of Anatahan volcano (CNMI).
Figure 3 shows good agreement between the OMI and AIRS SO2 data in terms of SO2 loading
and overall spatial distribution. The correlation plots (Fig. 4) show a robust correlation between
OMI and AIRS SO2 columns (r2 = 0.83) for a search radius as low as 0.2º, and also for off-nadir
scan positions. This suggests that the volcanic cloud was relatively homogeneous in terms of SO2
column, on the timescale of the A-Train overpass, perhaps due to low wind shear (velocity and
direction) conditions. This is also supported by the collocation of ash and SO2 observed in this
eruption, since low wind shear would promote collocation of ash (which sediments to lower
2
AIRS SO2 Granule:107
Mass= 0.0770 Tg Area= 184656 km2 Max SO2= 49.2DU Date: 2007.10.01 10:41-10:47 UTC
32
34
36
38
42
44
40
42
44
1
22
22
24
24
40
5
10
5
40.0
40
18
40
20
510
10
32.0
10
18
36.0
20
20
1
1
16
24.0
16
16.0
14
20.0
14
12.0
12
8.0
12
SO2 (milli atm-cm)
1
28.0
4.0
0.0
32
34
36
38
(a)
(b)
Fig. 1. (a) AIRS SO2 retrieval for the October 1, 2007 eruption of Jebel al-Tair (Yemen) at 10:41-10:47
UTC. (b) Operational OMI SO2 retrieval at 10:57-11:01 UTC. The location of the volcano is indicated by
a triangle. Both OMI and AIRS measured a total SO2 loading of ~0.07-0.08 Tg SO2.
3
(a)
(b)
(c)
(d)
Fig. 2. Comparison of operational OMI SO2
columns and AIRS SO2 columns [Prata and
Bernardo, 2007] in the Jebel al-Tair volcanic
eruption cloud on October 1, 2007. (a)-(e) show
correlation plots between OMI and AIRS pixels for
increasing search radii around each OMI pixel from
0.1-0.5º in 0.1º increments. Symbols are colorcoded by OMI cross-track scan position (1-60; 30 =
nadir). On each plot, the 1:1 line is shown, and if
the value of the correlation coefficient (r2) exceeds
0.5, then the equation of the best-fit linear
regression is also shown. Only SO2 columns >10
DU are included in the fit.
(e)
altitudes than SO2).
While many eruptions analyzed to date show good correlations between OMI and AIRS
SO2 measurements, Figures 5 and 6 show an example of a less robust comparison for the
Copahue (Chile) eruption of December 2012. In this case, the AIRS data granule does not provide
complete coverage of the volcanic cloud on December 22, 2012 (Fig. 5a), thus the total SO2
loading is less than measured by OMI. The pixel-by-pixel comparison is hindered since the scan
positions concerned are near the edge of the OMI and AIRS swaths, causing errors due to spatial
averaging. It is also likely that the volcanic cloud was advecting rapidly in jet stream winds, and
4
AIRS SO2 Granule:036
Mass= 0.0826 Tg Area= 117803 km2 Max SO2=108.9DU Date: 2005.04.06 03:35-03:41 UTC
144
146
148
150
152
18
18
1
142
1
10
5
5
10
17
17
1
1
16
15
14
1
40
15.0
13
20
10
5
13
10.0
40
60
20.0
5
10
14
25.0
40
40
10
20
30.0
60
1
1
SO2 (milli atm-cm)
5
15
35.0
20
20
40.0
1
45.0
16
50.0
5.0
0.0
142
144
146
148
150
152
(a)
(b)
Fig. 3. (a) AIRS SO2 retrieval for the April 5, 2005 eruption of Anatahan (CNMI) on April 6 at 3:35-3:41
UTC. (b) Operational OMI SO2 retrieval for the same eruption cloud at 3:53-3:55 UTC on April 6. Both
OMI and AIRS measured a total SO2 loading of ~0.07-0.08 Tg SO2.
5
(a)
(b)
(c)
(d)
Fig. 4. Comparison of operational OMI SO2
columns and AIRS SO2 columns [Prata and
Bernardo, 2007] in the Anatahan volcanic eruption
cloud on April 6, 2005. (a)-(e) show correlation
plots between OMI and AIRS pixels for increasing
search radii around each OMI pixel from 0.1-0.5º in
0.1º increments. Symbols are color-coded by OMI
cross-track scan position (1-60; 30 = nadir). On
each plot, the 1:1 line is shown, and if the value of
the correlation coefficient (r2) exceeds 0.5, then the
equation of the best-fit linear regression is also
shown. Only SO2 columns >10 DU are included in
the fit.
(e)
hence wind shear was likely significant, even on the short timescale between OMI and AIRS
measurements. Another factor was the relatively low altitude of the eruption cloud (~9 km; Table
1), which may have impacted the AIRS measurements. Thus, although there is a good correlation
between some pixels (Fig. 6), there are also many outliers, some of which may be ascribed to
water vapor interference or other retrieval issues (e.g., presence of ash or other aerosols).
6
AIRS SO2 Granule:190
Mass= 0.0429 Tg Area= 35170 km2 Max SO2= 74.3DU Date: 2012.12.22 18:59-18:65 UTC
-72
-68
-64
-56
-52
-60
-56
-52
-36
-36
-34
-34
-60
50.0
-38
Copahue
30.0
-40
35.0
60
40
-40
60
0
10521
25.0
-42
20.0
-42
SO2 (milli atm-cm)
40.0
-38
45.0
15.0
10.0
-44
-44
5.0
0.0
-72
-68
-64
(a)
(b)
Fig. 5. (a) AIRS SO2 retrieval for the December 22, 2012 eruption of Copahue (Chile) at 18:59-19:05
UTC. (b) Operational OMI SO2 retrieval for the same eruption cloud at 19:06-19:11 UTC. In this case
AIRS does not provide full coverage of the SO2 cloud, and hence the total SO2 loadings measured by OMI
and AIRS are different.
7
Fig. 6. Comparison of operational OMI SO2 columns and AIRS SO2 columns [Prata and
Bernardo, 2007] in the Copahue volcanic eruption cloud on December 22, 2012. This
correlation plot between OMI and AIRS pixels corresponds to a search radius of 0.5º around
each OMI pixel. Symbols are color-coded by OMI cross-track scan position (1-60; 30 = nadir).
Pixels displaying high AIRS SO2 columns but low OMI SO2 columns in this case may be
affected by water vapor interference.
3. Summary statement
In summary, our work continues to support the validity of the operational OMI SO2 retrieval
algorithm for volcanic clouds in the UTLS. Furthermore, this analysis also serves as a validation
for the AIRS SO2 algorithm developed by Prata and Bernardo [2007] and supports the use of the
AIRS SO2 measurements operationally for aviation hazard mitigation. Our preliminary
conclusion from this analysis is that OMI and AIRS SO2 columns display robust correlations in
UTLS volcanic clouds when the expected (small) spatial offset is accounted for. Where
correlations are less robust, this is usually due to a combination of factors including off-nadir
pixels, high wind shear, or lower SO2 altitudes. We also anticipate that this analysis could reveal
and major issues with the OMI and AIRS SO2 retrieval techniques, such as the effect of water
vapor interference on the AIRS SO2 retrievals.
4. Objectives for FY13-14
We plan to complete this analysis for all eruptions listed in Table 1, adding future eruptions as
they occur, to produce an extensive OMI-AIRS validation dataset. We also intend to include
comparisons with other AIRS SO2 retrieval schemes, such as that developed by the University of
Maryland Baltimore County (UMBC) Physics group [e.g., Carn et al., 2005].
8
Table 1. Eruption list for OMI-AIRS comparisons
9
5. References cited
Carn, S.A., L.L. Strow, S. de Souza-Machado, Y. Edmonds, and S. Hannon (2005). Quantifying
tropospheric volcanic emissions with AIRS: the 2002 eruption of Mt. Etna
(Italy). Geophys. Res. Lett. 32(2), L02301, doi:10.1029/2004GL021034.
Prata, A. J., and C. Bernardo (2007), Retrieval of volcanic SO2 column abundance from
Atmospheric Infrared Sounder data, J. Geophys. Res., 112, D20204,
doi:10.1029/2006JD007955.
Yang, K., N.A. Krotkov, A.J. Krueger, S.A. Carn, P.K. Bhartia, and P.F. Levelt (2007). Retrieval
of large volcanic SO2 columns from the Aura Ozone Monitoring Instrument (OMI):
comparison and limitations. J. Geophys. Res., 112, D24S43, doi:10.1029/2007JD008825.
6. Publications and reporting
Peer-reviewed publications in 2012-2013
*Student author
*McCormick, B.T., M. Herzog, J. Yiang, M. Edmonds, T.A. Mather, S.A. Carn, S. Hidalgo, and
B. Langmann (2013), An integrated study of SO2 emissions from Tungurahua volcano,
Ecuador, J. Geophys. Res. (under review).
Carn, S.A., N.A. Krotkov, K. Yang, and A.J. Krueger (2013), Measuring global volcanic
degassing with the Ozone Monitoring Instrument (OMI), Spec. Publ. Geol. Soc. Lon. (in press).
*McCormick, B.T., M. Edmonds, T. Mather, R. Campion, C. Hayer, H.E. Thomas, and S.A.
Carn (2013), Volcano monitoring applications of the Ozone Monitoring Instrument (OMI), Spec.
Publ. Geol. Soc. Lon. (in press).
Wang, J., S. Park, J. Zeng, C. Ge, K. Yang, S.A. Carn, N. Krotkov, and A. H. Omar (2013).
Modeling of 2008 Kasatochi volcanic sulfate direct radiative forcing: assimilation of OMI
SO2 plume height data and comparison with MODIS and CALIOP observations. Atmos. Chem.
Phys. 13, 1895-1912, http://www.atmos-chem-phys.net/13/1895/2013/acp-13-1895-2013.html.
*Hughes, E.J., L.C. Sparling, S.A. Carn, and A.J. Krueger (2012). Using horizontal transport
characteristics to infer an emission height time-series of volcanic SO2. J. Geophys. Res., 117,
D18307, doi:10.1029/2012JD017957.
Campion, R., M. Martinez-Cruz, T. Lecoq, C. Caudron, J. Pacheco, G. Pinardi, C. Hermans, S.A.
Carn, and A. Bernard (2012). Space- and ground-based measurements of sulfur dioxide
emissions from Turrialba volcano (Costa Rica). Bull. Volcanol. 74(7), 1757-1770,
doi:10.1007/s00445-012-0631-z.
10
Kushendratno, J.S. Pallister, Kristianto, F.R. Bina, W. McCausland, S.A. Carn, N. Haerani, J.
Griswold, and R. Keeler (2012). Recent explosive eruptions and volcano hazards at Soputan
volcano – a basalt stratovolcano in north Sulawesi, Indonesia, Bull. Volcanol., 74(7), 1581-1609.
Lopez. T.M., S.A. Carn, C. Werner, P. Kelly, M. Doukas, M. Pfeffer, D. Fee, P. Webley, C.
Cahill, and D.J. Schneider (2012). Evaluation of Redoubt volcano’s sulfur dioxide emissions by
the Ozone Monitoring Instrument, J. Volcanol. Geotherm. Res.,
doi:10.1016/j.jvolgeores.2012.03.002 (in press).
McCormick, B.T., M. Edmonds, T.A. Mather, and S.A. Carn (2012). First synoptic analysis of
volcanic degassing in Papua New Guinea, Geochem. Geophys. Geosyst., 13(3), Q03008,
doi:10.1029/2011GC003945.
Prata, A.J., G.J.S. Bluth, C. Werner, V.J. Realmuto, S.A. Carn, and I.M. Watson (2012). Remote
Sensing of Gas Emissions from Volcanoes, in Satellite Monitoring of Volcanoes: Spaceborne
Images of the North Pacific, eds. K.G. Dean and J. Dehn (in press).
Related abstracts and conference presentations since 2011
* Denotes student author
*McCormick, B., J. Yiang, M. Edmonds, T. Mather, S.A. Carn, S. Hidalgo, B. Langmann and M. Herzog, 2012, An
integrated study of SO2 degassing from Tungurahua volcano, Ecuador, AGU Fall Meeting, San Francisco,
CA, Dec 3-7 (poster).
Carn, S.A., and F. Schwandner, 2012, Satellite-based constraints on tropospheric volcanic emissions of SO2 and
CO2, AGU Fall Meeting, San Francisco, CA, Dec 3-7 (poster).
*McCormick, B., J. Yiang, M. Edmonds, T. Mather, S.A. Carn, S. Hidalgo, B. Langmann and M. Herzog, 2012,
Integrating ground- and satellite-based monitoring of volcanic SO2 degassing, Cities on Volcanoes 7
meeting, Colima, Mexico, Nov 19-23(poster).
Rodriguez, L., C. Reyes, A. Morales, J. Marrero, S.A. Carn, W. Morrow, C. Ramirez, G. Gonzalez, R. MoraAmador, and M. Taras, 2012, SO2 fluxes in volcanic clouds from active volcanoes in Costa Rica,
determined using OMI satellite images and ground-based measurements, Cities on Volcanoes 7 meeting,
Colima, Mexico, Nov 19-23 (poster).
Carn S.A., K. Yang, and V.J.B. Flower, 2012, Satellite-based assessment of global volcanic degassing, Cities on
Volcanoes 7 meeting, Colima, Mexico, Nov 19-23 (talk).
Carn, S.A., N.A. Krotkov, and A.J. Krueger, 2012, Three decades of satellite monitoring of Hawaiian volcanic
sulfur dioxide emissions, AGU Chapman Conference on Hawaiian volcanoes: from source to surface,
Waikoloa, Hawaii, Aug 20-24 (poster).
Carn S.A., K. Yang, J. Wang, S. Park, and A.J. Prata, 2012, Satellite measurements and modeling of the 2011 Nabro
(Eritrea) volcanic clouds, AGU Chapman Conference on Volcanism and the Atmosphere, Selfoss, Iceland,
Jun 10-15 (talk and poster).
*McCormick, B., J. Yiang, M. Edmonds, T. Mather, S.A. Carn, S. Hidalgo, B. Langmann and M. Herzog, 2012,
Validating OMI measurements of tropospheric volcanic SO2, AGU Chapman Conference on Volcanism and
the Atmosphere, Selfoss, Iceland, Jun 10-15 (poster).
Carn S.A., K. Yang, and A.J. Prata, 2012, A-Train Satellite Observations of Recent Explosive Eruptions in Iceland
and Chile, EGU General Assembly, Vienna, Austria, Apr 22-27 (invited talk).
Carn S.A., D. Fee, and A.J. Prata, 2012, Remote detection of monitoring of volcanic eruptions in the East African
Rift, Magmatic Rifting and Active Volcanism Conference, Addis Ababa, Ethiopia, Jan 11-13 (talk)
Carn S.A., A.J. Prata, K. Yang, and W.I. Rose, 2011, A-Train Observations of Young Volcanic Eruption Clouds,
AGU Fall Meeting, San Francisco, CA, Dec 5-9 (poster).
11
Carn, S.A., 2011, Monitoring global volcanic degassing from space: progress and prospects, William Smith Meeting
on Remote Sensing of Volcanoes and Volcanic Processes: integrating observations and modeling, Geological
Society, London, UK, Oct 4-5 (talk).
Carn, S.A., 2011, Remote sensing of volcanic emissions in the Asia-Pacfic region, Conference on Remote Sensing,
Natural Hazards and Environmental Change, CRISP/NUS, Singapore, Jul 28-29 (invited keynote).
Carn, S.A., J. Wang, K. Yang, A.J. Prata and L. Clarisse, 2011, Satellite measurements and modeling of the 2010
Merapi volcanic eruption clouds, XXV IUGG General Assembly, Melbourne, Australia, Jun 27 – Jul 8 (talk).
12