Cloud base height retrieval from multi-angle satellite data
<p>Clouds are a key modulator of the Earth energy budget at the top of the atmosphere and at the surface. While the cloud top height is operationally retrieved with global coverage, only few methods have been proposed to determine cloud base height (<span class="inline-formula">...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-03-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/12/1841/2019/amt-12-1841-2019.pdf |
| Summary: | <p>Clouds are a key modulator of the Earth energy budget at the top
of the atmosphere and at the surface. While the cloud top height is
operationally retrieved with global coverage, only few methods have been
proposed to determine cloud base height (<span class="inline-formula"><i>z</i><sub>base</sub></span>) from satellite
measurements. This study presents a new approach to retrieve cloud base
heights using the Multi-angle Imaging SpectroRadiometer (MISR) on the Terra
satellite. It can be applied if some cloud gaps occur within the chosen
distance of typically <span class="inline-formula">10</span> km. The MISR cloud base height (MIBase) algorithm
then determines <span class="inline-formula"><i>z</i><sub>base</sub></span> from the ensemble of all MISR cloud top
heights retrieved at a <span class="inline-formula">1.1</span> km horizontal resolution in this area. MIBase
is first calibrated using 1 year of ceilometer data from more than 1500
sites within the continental United States of America. The 15th percentile of
the cloud top height distribution within a circular area of <span class="inline-formula">10</span> km radius
provides the best agreement with the ground-based data. The thorough
evaluation of the MIBase product <span class="inline-formula"><i>z</i><sub>base</sub></span> with further ceilometer
data yields a correlation coefficient of about <span class="inline-formula">0.66</span>, demonstrating the
feasibility of this approach to retrieve <span class="inline-formula"><i>z</i><sub>base</sub></span>. The impacts of
the cloud scene structure and macrophysical cloud properties are discussed.
For a 3-year period, the median <span class="inline-formula"><i>z</i><sub>base</sub></span> is generated globally
on a 0.25<span class="inline-formula"><sup>∘</sup></span> <span class="inline-formula">×</span> 0.25<span class="inline-formula"><sup>∘</sup></span> grid. Even though overcast cloud
scenes and high clouds are excluded from the statistics, the median
<span class="inline-formula"><i>z</i><sub>base</sub></span> retrievals yield plausible results, in particular over ocean
as well as for seasonal differences. The potential of the full 16 years of
MISR data is demonstrated for the southeast Pacific, revealing interannual
variability in <span class="inline-formula"><i>z</i><sub>base</sub></span> in accordance with reanalysis data. The
global cloud base data for the 3-year period (2007–2009) are available
at <a href="https://doi.org/10.5880/CRC1211DB.19">https://doi.org/10.5880/CRC1211DB.19</a>.</p> |
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| ISSN: | 1867-1381 1867-8548 |