A novel method for ground-based remote sensing of profiles of cloud microphysical properties

• Applicant: Professor Dr. Bernhard Mayer
• Subject Area: Atmospheric Science
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 256770551

• Final Report Year: 2017

Final Report Abstract

In order to observe the vertical development of cloud droplets from aerosol activation to rain-out, a remote sensing technique was proposed to retrieve vertical profiles of cloud droplet effective radius using solar reflectance from cloud sides. Testing the feasibility of that proposal, in theory as well as in practice, was a central motivation of this project. In a first step, this project introduced a statistical framework for the proposed remote sensing of cloud sides following Marshak et al. (2006). A statistical relationship between reflected sunlight in a near-visible and near-infrared wavelength and droplet size was found following the classical approach which is based on a bijective relationship. By simulating the three-dimensional radiative transfer in highly resolved LES model clouds using the Monte Carlo code for the physically correct tracing of photons in cloudy atmospheres (MYSTIC), probability distributions for this relationship were sampled. In contrast to many other effective radius retrievals, this work thereby provides essential information about the retrieval uncertainties which are intrinsically linked with the reflectance ambiguities caused by three-dimensional radiative effects. In the course of this work, the framework was not only tested numerically, but also applied to real-world measurements of convective cloud sides. For that purpose, this work introduced and characterized the imaging spectrometer of the Munich Aerosol Cloud Scanner (specMACS). Furthermore, the proposed technique was validated with independent in situ measurements of cloud droplet size from airborne platforms. In conclusion, the present work applied a working effective radius retrieval to measurements of clouds sides and thus paved the way for further research on this topic. For the first time, this work demonstrated the feasibility to retrieve cloud particle size profiles from cloud sides and thus marks a further important step towards an operational application of this technique.

Publications

• Reconstruction of cloud geometry using a scanning cloud radar, Atmos. Meas. Tech., 8, 2491-2508
  Ewald, F., Winkler, C., and Zinner, T.
  
• Design and characterization of specMACS, a multipurpose hyperspectral cloud and sky imager, Atmos. Meas. Tech., 9, 2015- 2042
  Ewald, F., Kölling, T., Baumgartner, A., Zinner, T., and Mayer, B.
  
• Ground-based imaging remote sensing of ice clouds: uncertainties caused by sensor, method and atmosphere, Atmos. Meas. Tech., 9, 4615-4632
  Zinner, T., Hausmann, P., Ewald, F., Bugliaro, L., Emde, C., and Mayer, B.
  
• Retrieval of vertical profiles of cloud droplet effective radius using solar reflectance from cloud sides, PhD thesis, Ludwig–Maximilians–University, 2016
  Ewald, F.