Evaluation of MUSICA IASI tropospheric water vapour profiles using theoretical error assessments and comparisons to GRUAN Vaisala RS92 measurements
<p>Volume mixing ratio water vapour profiles have been retrieved from IASI (Infrared Atmospheric Sounding Interferometer) spectra using the MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water) processor. The retrievals are done for IASI o...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-09-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/11/4981/2018/amt-11-4981-2018.pdf |
| Summary: | <p>Volume mixing ratio water vapour profiles have been retrieved from IASI
(Infrared Atmospheric Sounding Interferometer) spectra using the MUSICA
(MUlti-platform remote Sensing of Isotopologues for investigating the Cycle
of Atmospheric water) processor. The retrievals are done for IASI
observations that coincide with Vaisala RS92 radiosonde measurements
performed in the framework of the GCOS (Global Climate Observing System)
Reference Upper-Air Network (GRUAN) in three different climate zones: the
tropics (Manus Island, 2° S), mid-latitudes (Lindenberg,
52° N), and polar regions (Sodankylä, 67° N).
</p><p>
The retrievals show good sensitivity with respect to the vertical H<sub>2</sub>O
distribution between 1 km above ground and the upper troposphere.
Typical DOFS (degrees of freedom for signal) values are about 5.6
for the tropics, 5.1 for summertime mid-latitudes, 3.8 for
wintertime mid-latitudes, and 4.4 for summertime polar regions.
The errors of the MUSICA IASI water vapour profiles have been
theoretically estimated considering the contribution of many different
uncertainty sources. For all three climate regions, unrecognized cirrus
clouds and uncertainties in atmospheric temperature have been identified
as the most important error sources and they can reach about 25 %.
</p><p>
The MUSICA IASI water vapour profiles have been compared to 100 individual
coincident GRUAN water vapour profiles. The systematic difference between the
data is within 11 % below 12 km altitude; however, at higher altitudes the MUSICA IASI data show a dry bias with respect to
the GRUAN data of up to 21 %. The scatter is largest
close to the surface (30 %), but never exceeds 21 % above 1 km altitude.
The comparison study documents that the MUSICA IASI retrieval processor provides
H<sub>2</sub>O profiles that capture the large variations in H<sub>2</sub>O
volume mixing ratio profiles well from 1 km above ground up to
altitudes close to the tropopause. Above 5 km the observed scatter with respect to GRUAN data is in reasonable agreement
with the combined MUSICA IASI and GRUAN random errors. The increased scatter at lower altitudes might be explained by
surface emissivity uncertainties at the summertime continental sites of Lindenberg and Sodankylä, and the upper
tropospheric dry bias might suggest deficits in correctly modelling the spectroscopic line shapes of water vapour.</p> |
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| ISSN: | 1867-1381 1867-8548 |