Retrieval of ash properties from IASI measurements
A new optimal estimation algorithm for the retrieval of volcanic ash properties has been developed for use with the Infrared Atmospheric Sounding Interferometer (IASI). The retrieval method uses the wave number range 680–1200 cm<sup>−1</sup>, which contains window channels, the CO<...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2016-11-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/9/5407/2016/amt-9-5407-2016.pdf |
| _version_ | 1819239756480905216 |
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| author | L. J. Ventress G. McGarragh E. Carboni A. J. Smith R. G. Grainger |
| author_facet | L. J. Ventress G. McGarragh E. Carboni A. J. Smith R. G. Grainger |
| author_sort | L. J. Ventress |
| collection | DOAJ |
| description | A new optimal estimation algorithm for the retrieval of volcanic ash
properties has been developed for use with the Infrared Atmospheric Sounding
Interferometer (IASI). The retrieval method uses the wave number range
680–1200 cm<sup>−1</sup>, which contains window channels, the CO<sub>2</sub> <i>ν</i><sub>2</sub>
band (used for the height retrieval), and the O<sub>3</sub> <i>ν</i><sub>3</sub> band.<br></br>Assuming a single infinitely (geometrically) thin ash plume and combining
this with the output from the radiative transfer model RTTOV, the retrieval
algorithm produces the most probable values for the ash optical depth (AOD),
particle effective radius, plume top height, and effective radiating
temperature. A comprehensive uncertainty budget is obtained for each pixel.
Improvements to the algorithm through the use of different measurement error
covariance matrices are explored, comparing the results from a sensitivity
study of the retrieval process using covariance matrices trained on either
clear-sky or cloudy scenes. The result showed that, due to the smaller
variance contained within it, the clear-sky covariance matrix is preferable.
However, if the retrieval fails to pass the quality control tests, the cloudy
covariance matrix is implemented.<br></br>The retrieval algorithm is applied to scenes from the Eyjafjallajökull
eruption in 2010, and the retrieved parameters are compared to ancillary data
sources. The ash optical depth gives a root mean square error (RMSE)
difference of 0.46 when compared to retrievals from the MODerate-resolution Imaging Spectroradiometer (MODIS) instrument
for all pixels and an improved RMSE of 0.2 for low optical depths
(AOD < 0.1). Measurements from the Facility for Airborne
Atmospheric Measurements (FAAM) and Deutsches Zentrum für Luft- und
Raumfahrt e.V. (DLR) flight campaigns are used to
verify the retrieved particle effective radius, with the retrieved
distribution of sizes for the scene showing excellent consistency. Further,
the plume top altitudes are compared to derived cloud-top altitudes from the
Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument and show agreement with RMSE values of less than 1 km. |
| first_indexed | 2024-12-23T13:57:11Z |
| format | Article |
| id | doaj.art-ced1a785cd9f4a21b5c19ae0c72359bc |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-23T13:57:11Z |
| publishDate | 2016-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-ced1a785cd9f4a21b5c19ae0c72359bc2022-12-21T17:44:26ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482016-11-0195407542210.5194/amt-9-5407-2016Retrieval of ash properties from IASI measurementsL. J. Ventress0G. McGarragh1E. Carboni2A. J. Smith3R. G. Grainger4National Centre for Earth Observation, Atmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UKAtmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UKCOMET, Atmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UKNational Centre for Earth Observation, Atmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UKCOMET, Atmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UKA new optimal estimation algorithm for the retrieval of volcanic ash properties has been developed for use with the Infrared Atmospheric Sounding Interferometer (IASI). The retrieval method uses the wave number range 680–1200 cm<sup>−1</sup>, which contains window channels, the CO<sub>2</sub> <i>ν</i><sub>2</sub> band (used for the height retrieval), and the O<sub>3</sub> <i>ν</i><sub>3</sub> band.<br></br>Assuming a single infinitely (geometrically) thin ash plume and combining this with the output from the radiative transfer model RTTOV, the retrieval algorithm produces the most probable values for the ash optical depth (AOD), particle effective radius, plume top height, and effective radiating temperature. A comprehensive uncertainty budget is obtained for each pixel. Improvements to the algorithm through the use of different measurement error covariance matrices are explored, comparing the results from a sensitivity study of the retrieval process using covariance matrices trained on either clear-sky or cloudy scenes. The result showed that, due to the smaller variance contained within it, the clear-sky covariance matrix is preferable. However, if the retrieval fails to pass the quality control tests, the cloudy covariance matrix is implemented.<br></br>The retrieval algorithm is applied to scenes from the Eyjafjallajökull eruption in 2010, and the retrieved parameters are compared to ancillary data sources. The ash optical depth gives a root mean square error (RMSE) difference of 0.46 when compared to retrievals from the MODerate-resolution Imaging Spectroradiometer (MODIS) instrument for all pixels and an improved RMSE of 0.2 for low optical depths (AOD < 0.1). Measurements from the Facility for Airborne Atmospheric Measurements (FAAM) and Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) flight campaigns are used to verify the retrieved particle effective radius, with the retrieved distribution of sizes for the scene showing excellent consistency. Further, the plume top altitudes are compared to derived cloud-top altitudes from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument and show agreement with RMSE values of less than 1 km.https://www.atmos-meas-tech.net/9/5407/2016/amt-9-5407-2016.pdf |
| spellingShingle | L. J. Ventress G. McGarragh E. Carboni A. J. Smith R. G. Grainger Retrieval of ash properties from IASI measurements Atmospheric Measurement Techniques |
| title | Retrieval of ash properties from IASI measurements |
| title_full | Retrieval of ash properties from IASI measurements |
| title_fullStr | Retrieval of ash properties from IASI measurements |
| title_full_unstemmed | Retrieval of ash properties from IASI measurements |
| title_short | Retrieval of ash properties from IASI measurements |
| title_sort | retrieval of ash properties from iasi measurements |
| url | https://www.atmos-meas-tech.net/9/5407/2016/amt-9-5407-2016.pdf |
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