New-generation NASA Aura Ozone Monitoring Instrument (OMI) volcanic SO<sub>2</sub> dataset: algorithm description, initial results, and continuation with the Suomi-NPP Ozone Mapping and Profiler Suite (OMPS)
Since the fall of 2004, the Ozone Monitoring Instrument (OMI) has been providing global monitoring of volcanic SO<sub>2</sub> emissions, helping to understand their climate impacts and to mitigate aviation hazards. Here we introduce a new-generation OMI volcanic SO<sub>2</sub>...
Main Authors: | , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-02-01
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Series: | Atmospheric Measurement Techniques |
Online Access: | http://www.atmos-meas-tech.net/10/445/2017/amt-10-445-2017.pdf |
Summary: | Since the fall of 2004, the Ozone Monitoring Instrument
(OMI) has been providing global monitoring of volcanic SO<sub>2</sub> emissions,
helping to understand their climate impacts and to mitigate aviation
hazards. Here we introduce a new-generation OMI volcanic SO<sub>2</sub> dataset
based on a principal component analysis (PCA) retrieval technique. To reduce
retrieval noise and artifacts as seen in the current operational linear fit
(LF) algorithm, the new algorithm, OMSO2VOLCANO, uses characteristic
features extracted directly from OMI radiances in the spectral fitting,
thereby helping to minimize interferences from various geophysical processes
(e.g., O<sub>3</sub> absorption) and measurement details (e.g., wavelength shift).
To solve the problem of low bias for large SO<sub>2</sub> total columns in the LF
product, the OMSO2VOLCANO algorithm employs a table lookup approach to
estimate SO<sub>2</sub> Jacobians (i.e., the instrument sensitivity to a
perturbation in the SO<sub>2</sub> column amount) and iteratively adjusts the
spectral fitting window to exclude shorter wavelengths where the SO<sub>2</sub>
absorption signals are saturated. To first order, the effects of clouds and
aerosols are accounted for using a simple Lambertian equivalent reflectivity
approach. As with the LF algorithm, OMSO2VOLCANO provides total column
retrievals based on a set of predefined SO<sub>2</sub> profiles from the lower
troposphere to the lower stratosphere, including a new profile peaked at 13
km for plumes in the upper troposphere. Examples given in this study
indicate that the new dataset shows significant improvement over the LF
product, with at least 50 % reduction in retrieval noise over the remote
Pacific. For large eruptions such as Kasatochi in 2008 (∼ 1700 kt total SO<sub>2</sub>) and Sierra Negra in 2005 (> 1100 DU maximum
SO<sub>2</sub>), OMSO2VOLCANO generally agrees well with other algorithms that
also utilize the full spectral content of satellite measurements, while the
LF algorithm tends to underestimate SO<sub>2</sub>. We also demonstrate that,
despite the coarser spatial and spectral resolution of the Suomi National
Polar-orbiting Partnership (Suomi-NPP) Ozone Mapping and Profiler Suite
(OMPS) instrument, application of the new PCA algorithm to OMPS data
produces highly consistent retrievals between OMI and OMPS. The new PCA
algorithm is therefore capable of continuing the volcanic SO<sub>2</sub> data
record well into the future using current and future hyperspectral UV
satellite instruments. |
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ISSN: | 1867-1381 1867-8548 |