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| Titel |
A novel technique for extracting clouds base height using ground based imaging |
| VerfasserIn |
E. Hirsch, E. Agassi, I. Koren |
| 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 ; 4, no. 1 ; Nr. 4, no. 1 (2011-01-28), S.117-130 |
| Datensatznummer |
250001571
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| Publikation (Nr.) |
 copernicus.org/amt-4-117-2011.pdf |
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| Zusammenfassung |
| The height of a cloud in the atmospheric column is a key parameter in its
characterization. Several remote sensing techniques (passive and active,
either ground-based or on space-borne platforms) and in-situ measurements
are routinely used in order to estimate top and base heights of clouds. In
this article we present a novel method that combines thermal imaging from
the ground and sounded wind profile in order to derive the cloud base
height. This method is independent of cloud types, making it efficient for
both low boundary layer and high clouds. In addition, using thermal imaging
ensures extraction of clouds' features during daytime as well as at
nighttime. The proposed technique was validated by comparison to active
sounding by ceilometers (which is a standard ground based method), to lifted
condensation level (LCL) calculations, and to MODIS products obtained from
space. As all passive remote sensing techniques, the proposed method
extracts only the height of the lowest cloud layer, thus upper cloud layers
are not detected. Nevertheless, the information derived from this method can
be complementary to space-borne cloud top measurements when deep-convective
clouds are present. Unlike techniques such as LCL, this method is not
limited to boundary layer clouds, and can extract the cloud base height at
any level, as long as sufficient thermal contrast exists between the
radiative temperatures of the cloud and its surrounding air parcel. Another
advantage of the proposed method is its simplicity and modest power needs,
making it particularly suitable for field measurements and deployment at
remote locations. Our method can be further simplified for use with visible
CCD or CMOS camera (although nighttime clouds will not be observed). |
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