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Retrievals of Cloud Droplet Size from the RSP Data: Validation Using in Situ MeasurementsWe present comparisons of cloud droplet size distributions retrieved from the Research Scanning Polarimeter (RSP) data with correlative in situ measurements made during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES). This field experiment was based at St. Johns airport, Newfoundland, Canada with the latest deployment in May - June 2016. RSP was onboard the NASA C-130 aircraft together with an array of in situ and other remote sensing instrumentation. The RSP is an along-track scanner measuring polarized and total reflectances in9 spectral channels. Its unique high angular resolution allows for characterization of liquid water droplet size using the rainbow structure observed in the polarized reflectances in the scattering angle range between 135 and 165 degrees. A parametric fitting algorithm applied to the polarized reflectances provides retrievals of the droplet effective radius and variance assuming a prescribed size distribution shape (gamma distribution). In addition to this, we use a non-parametric method, Rainbow Fourier Transform (RFT), which allows us to retrieve the droplet size distribution (DSD) itself. The latter is important in the case of clouds with complex structure, which results in multi-modal DSDs. During NAAMES the aircraft performed a number of flight patterns specifically designed for comparison of remote sensing retrievals and in situ measurements. These patterns consisted of two flight segments above the same straight ground track. One of these segments was flown above clouds allowing for remote sensing measurements, while the other was at the cloud top where cloud droplets were sampled. We compare the DSDs retrieved from the RSP data with in situ measurements made by the Cloud Droplet Probe (CDP). The comparisons show generally good agreement with deviations explainable by the position of the aircraft within cloud and by presence of additional cloud layers in RSP view that do not contribute to the in situ DSDs. In the latter case the distributions retrieved from the RSP data were consistent with the multi-layer cloud structures observed in the correlative High Spectral Resolution Lidar (HSRL) profiles. The comparison results provide a rare validation of polarimetric droplet size retrieval techniques, which can be used for analysis of satellite data on global scale.
Document ID
20160014659
Acquisition Source
Goddard Space Flight Center
Document Type
Presentation
Authors
Alexandrov, Mikhail D. (Columbia Univ. New York, NY, United States)
Cairns, Brian (NASA Goddard Inst. for Space Studies New York, NY, United States)
Sinclair, Kenneth (Columbia Univ. New York, NY, United States)
Wasilewski, Andrzej P. (TRINNOVIM, LLC New York, NY, United States)
Ziemba, Luke (NASA Langley Research Center Hampton, VA, United States)
Crosbie, Ewan (NASA Langley Research Center Hampton, VA, United States)
Hair, John (NASA Langley Research Center Hampton, VA, United States)
Hu, Yongxiang (NASA Langley Research Center Hampton, VA, United States)
Hostetler, Chris (NASA Langley Research Center Hampton, VA, United States)
Stamnes, Snorre (NASA Langley Research Center Hampton, VA, United States)
Date Acquired
December 16, 2016
Publication Date
December 12, 2016
Subject Category
Earth Resources And Remote Sensing
Meteorology And Climatology
Report/Patent Number
GSFC-E-DAA-TN38026
Meeting Information
Meeting: AGU Fall Meeting 2016
Location: San Francisco, CA
Country: United States
Start Date: December 12, 2016
End Date: December 16, 2016
Sponsors: American Geophysical Union
Funding Number(s)
CONTRACT_GRANT: NNX14AB99A
CONTRACT_GRANT: NNG12HP07C
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
cloud droplets
in situ measurements
droplet size distribution
polarized reflectance

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