Coupled Retrieval of Liquid Water Cloud and Above‐Cloud Aerosol Properties Using the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI). Issue 6 (30th March 2018)

• Record Type: Journal Article
• Authors: Xu, Feng; van Harten, Gerard; Diner, David J.; Davis, Anthony B.; Seidel, Felix C.; Rheingans, Brian; Tosca, Mika; Alexandrov, Mikhail D.; Cairns, Brian; Ferrare, Richard A.; Burton, Sharon P.; Fenn, Marta A.; Hostetler, Chris A.; Wood, Robert; Redemann, Jens
• Is Part Of: Journal of geophysical research. Volume 123:Issue 6(2018)
• Page Start: 3175
• Page End: 3204
• Publication Date: 2018-03-30
• Subjects: aerosols above cloud -- marine stratocumulus clouds -- airborne remote sensing -- vector radiative transfer -- polarimetry; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1002/2017JD027926
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: An optimization algorithm is developed to retrieve liquid water cloud properties including cloud optical depth (COD), droplet size distribution and cloud top height (CTH), and above‐cloud aerosol properties including aerosol optical depth (AOD), single‐scattering albedo, and microphysical properties from sweep‐mode observations by Jet Propulsion Laboratory's Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) instrument. The retrieval is composed of three major steps: (1) initial estimate of the mean droplet size distribution across the entire image of 80–100 km along track by 10–25 km across track from polarimetric cloudbow observations, (2) coupled retrieval of image‐scale cloud and above‐cloud aerosol properties by fitting the polarimetric data at all observation angles, and (3) iterative retrieval of 1‐D radiative transfer‐based COD and droplet size distribution at pixel scale (25 m) by establishing relationships between COD and droplet size and fitting the total radiance measurements. Our retrieval is tested using 134 AirMSPI data sets acquired during the National Aeronautics and Space Administration (NASA) field campaign ObseRvations of Aerosols above CLouds and their intEractionS. The retrieved above‐cloud AOD and CTH are compared to coincident HSRL‐2 (HSRL‐2, NASA Langley Research Center) data, and COD and droplet size distribution parameters (effective radius r eff and effective variance v eff ) are compared to coincident Research Scanning Polarimeter (RSP) (NASA Goddard Institute for Space Studies) data. Mean absolute differences between AirMSPI and HSRL‐2 retrievals of above‐cloud AOD at 532 nm and CTH are 0.03 and <0.5 km, respectively. At RSP's footprint scale (~ 323 m), mean absolute differences between RSP and AirMSPI retrievals of COD, r eff, and v eff in the cloudbow area are 2.33, 0.69 μm, and 0.020, respectively. Neglect of smoke aerosols above cloud leads to an underestimate of image‐averaged COD by ~15%. Key Points: Above‐cloud aerosol and cloud property retrievals are coupled Empirical relations are found between cloud optical depth and droplet size parameters Pixel‐scale cloud optical depth and droplet size distributions are retrieved