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| Titel |
Exploiting the sensitivity of two satellite cloud height retrievals to cloud vertical distribution |
| VerfasserIn |
C. K. Carbajal Henken, L. Doppler, R. Lindstrot, R. Preusker, J. Fischer |
| 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 ; 8, no. 8 ; Nr. 8, no. 8 (2015-08-24), S.3419-3431 |
| Datensatznummer |
250116540
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| Publikation (Nr.) |
 copernicus.org/amt-8-3419-2015.pdf |
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| Zusammenfassung |
| This work presents a study on the sensitivity of two satellite cloud height
retrievals to cloud vertical distribution. The difference in sensitivity is
exploited by relating the difference in the retrieved cloud heights to cloud
vertical extent. The two cloud height retrievals, performed within the Freie
Universität Berlin AATSR MERIS Cloud (FAME-C) algorithm, are based on
independent measurements and different retrieval techniques. First, cloud-top
temperature (CTT) is retrieved from Advanced Along Track Scanning Radiometer
(AATSR) measurements in the thermal infrared. Second, cloud-top pressure
(CTP) is retrieved from Medium Resolution Imaging Spectrometer (MERIS)
measurements in the oxygen-A absorption band and a nearby window channel.
Both CTT and CTP are converted to cloud-top height (CTH) using atmospheric
profiles from a numerical weather prediction model. First, a sensitivity
study using radiative transfer simulations in the near-infrared and thermal
infrared was performed to demonstrate, in a quantitative manner, the larger
impact of the assumed cloud vertical extinction profile, described in terms
of shape and vertical extent, on MERIS than on AATSR top-of-atmosphere
measurements. Consequently, cloud vertical extinction profiles will have a
larger influence on the MERIS than on the AATSR cloud height retrievals for
most cloud types.
Second, the difference in retrieved CTH (ΔCTH) from AATSR and MERIS are related to
cloud vertical extent (CVE), as observed by ground-based lidar and radar at three ARM sites.
To increase the impact of the cloud vertical extinction profile on the MERIS-CTP retrievals,
single-layer and geometrically thin clouds are assumed in the forward model.
Similarly to previous findings, the MERIS-CTP retrievals appear to be close to pressure
levels in the middle of the cloud. Assuming a linear relationship, the ΔCTH multiplied by 2.5
gives an estimate on the CVE for single-layer clouds. The relationship is stronger for single-layer clouds than for multi-layer clouds.
Due to large variations of cloud vertical extinction profiles occurring in nature, a
quantitative estimate of the cloud vertical extent is accompanied with large uncertainties.
Yet, estimates of the CVE provide an additional parameter, next to CTH, that can be obtained
from passive imager measurements and can be used to further describe cloud vertical distribution,
thus contributing to the characterization of a cloudy scene.
To further demonstrate the plausibility of the approach, an estimate of the CVE was applied
to a case study.
In light of the follow-up mission Sentinel-3 with AATSR and MERIS like instruments, Sea and Land
Surface Temperature Radiometer (SLSTR) and (Ocean and Land Colour Instrument) OLCI, respectively, for
which the FAME-C algorithm can be easily adapted, a more accurate estimate of the CVE can be expected. OLCI
will have three channels in the oxygen-A absorption band, possibly providing enhanced information on cloud vertical distributions. |
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