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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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doi:10.5194/amt-2017-2
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
03 Feb 2017
Review status
This discussion paper is under review for the journal Atmospheric Measurement Techniques (AMT).
Remote Sensing of Multiple Cloud Layer Heights using Multi-Angular Measurements
Kenneth Sinclair1,2, Bastiaan van Diedenhoven2,3, Brian Cairns2, John Yorks4, Andrzej Wasilewski5, and Matthew McGill4 1Department of Earth and Environmental Engineering, Columbia University, New York, NY, 10025, United States
2NASA/Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, United States
3Center for Climate Systems Research, Columbia University, New York, NY 10025, United States
4NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States
5Trinnovim LLC, New York, NY, United States
Abstract. Cloud top height (CTH) affects the radiative properties of clouds. Improved CTH observations will allow for improved parameterizations in large-scale models and accurate information on CTH is also important when studying variations in freezing point and cloud microphysics. NASA’s airborne Research Scanning Polarimeter (RSP) is able to measure cloud top height using a novel multi-angular contrast approach. For the determination of CTH, a set of consecutive nadir reflectances is selected and the cross-correlations between this set and co-located sets at other viewing angles are calculated for a range of assumed cloud top heights, yielding a correlation profile. Under the assumption that cloud reflectances are isotropic, local peaks in the correlation profile indicate cloud layers. This technique can be applied to every RSP footprint and we demonstrate that detection of multiple peaks in the correlation profile allow retrieval of heights of multiple cloud layers within single RSP footprints. This paper provides an in-depth description of the architecture and performance of the RSP’s CTH retrieval technique using data obtained during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. RSP retrieved cloud heights are evaluated using collocated data from the Cloud Physics Lidar (CPL). The method’s accuracy associated with the magnitude of correlation, optical thickness, cloud thickness and cloud height are explored. The technique is applied to measurements at a wavelength of 670 nm and 1880 nm and their combination. The 1880-nm band is virtually insensitive to the lower troposphere due to strong water vapor absorption. It is found that each band is well suitable for retrieving heights of cloud layers with optical thicknesses above about 0.1 and that RSP cloud layer height retrievals more accurately correspond to CPL cloud middle than cloud top. It is also found that the 1880 nm band yields most accurate results for clouds at mid and high-altitudes (4.0 to 17 km) while the 670 nm band is most accurate at low and mid altitudes (1.0–13.0 km). The dual band performs best over the broadest range, and is suitable for accurately retrieving cloud layer heights between 1.0 and 16.0 km. Generally, the accuracy of the retrieved cloud top heights increases with increasing correlation value. Improved accuracy is achieved by using customized filtering techniques for each band with the most significant improvements occurring in the primary layer retrievals. RSP is able to measure a primary layer CTH with median error of about 0.5 km when compared to CPL. For multi-layered scenes, the second and third layer heights are determined median errors of about 1.5 km and 2.0–2.5 km, respectively.

Citation: Sinclair, K., van Diedenhoven, B., Cairns, B., Yorks, J., Wasilewski, A., and McGill, M.: Remote Sensing of Multiple Cloud Layer Heights using Multi-Angular Measurements, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2017-2, in review, 2017.
Kenneth Sinclair et al.
Kenneth Sinclair et al.
Kenneth Sinclair et al.

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Short summary
We present a multi-angular contrast approach to retrieve cloud top height (CTH) using photogrammetry. We demonstrate the method’s ability to retrieve heights of multiple cloud layers within single footprints, using the multiple views available for each footprint. This paper provides an in-depth description and performance analysis of the CTH retrieval technique and the retrieved cloud heights are evaluated using collocated data from the Cloud Physics Lidar.
We present a multi-angular contrast approach to retrieve cloud top height (CTH) using...
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