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| Titel |
A novel gridding algorithm to create regional trace gas maps from satellite observations |
| VerfasserIn |
G. Kuhlmann, A. Hartl, H. M. Cheung, Y. F. Lam, M. O. Wenig |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 7, no. 2 ; Nr. 7, no. 2 (2014-02-10), S.451-467 |
| Datensatznummer |
250115597
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| Publikation (Nr.) |
 copernicus.org/amt-7-451-2014.pdf |
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| Zusammenfassung |
| The recent increase in spatial resolution for satellite instruments has
made it feasible to study distributions of trace gas column
densities on a regional scale. For this application a new gridding
algorithm was developed to map measurements from the instrument's
frame of reference (level 2) onto a longitude–latitude grid (level 3). The algorithm is designed for the Ozone Monitoring Instrument
(OMI) and can easily be employed for similar instruments – for
example, the upcoming TROPOspheric Monitoring Instrument (TROPOMI).
Trace gas distributions are reconstructed by a continuous parabolic
spline surface. The algorithm explicitly considers the spatially
varying sensitivity of the sensor resulting from the instrument
function. At the swath edge, the inverse problem of computing the
spline coefficients is very sensitive to measurement errors and is
regularised by a second-order difference matrix. Since this
regularisation corresponds to the penalty term for smoothing
splines, it similarly attenuates the effect of measurement noise
over the entire swath width. Monte Carlo simulations are conducted
to study the performance of the algorithm for different
distributions of trace gas column densities. The optimal weight of
the penalty term is found to be proportional to the measurement
uncertainty and the width of the instrument function. A comparison
with an established gridding algorithm shows improved performance
for small to moderate measurement errors due to better
parametrisation of the distribution. The resulting maps are smoother
and extreme values are more accurately reconstructed. The
performance improvement is further illustrated with high-resolution
distributions obtained from a regional chemistry model. The new
algorithm is applied to tropospheric NO2 column densities
measured by OMI. Examples of regional NO2 maps are shown for
densely populated areas in China, Europe and the United States of
America. This work demonstrates that the newly developed gridding
algorithm improves regional trace gas maps; its application could be
very helpful for the study of satellite-derived trace gas
distributions. |
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