AUTHOR=Marshak Alexander , Knyazikhin Yuri , Várnai Tamás TITLE=A new spectrally-invariant approach to the remote sensing of inhomogeneous clouds JOURNAL=Frontiers in Remote Sensing VOLUME=5 YEAR=2024 URL=https://www.frontiersin.org/journals/remote-sensing/articles/10.3389/frsen.2024.1392596 DOI=10.3389/frsen.2024.1392596 ISSN=2673-6187 ABSTRACT=

Current operational satellite retrievals of cloud optical and microphysical properties go back to the Nakajima-King technique developed at the end of the 1980 s. This technique is based on library calculations for plane-parallel homogeneous clouds. It often works well for overcast skies but leads to substantial errors for inhomogeneous and broken cloud fields where the plane-parallel-geometry assumption is no longer valid. The basic concept of a new technique was first introduced in nuclear physics to quantify the critical conditions of reactors. Based on the eigenvalues of the radiative transfer equation, their approach provides a powerful means to parameterize the structure of 3D media. This parameterization was later successfully applied to relate surface reflectance spectra to 3D canopy structure and is known as the spectrally-invariant approximation. The proposed approach adapts this technique to the remote sensing of cloud properties such as droplet single scattering albedo and the average number of scatterings (which are the fundamental parameters in radiative transfer theory), with an emphasis on quantifying the associated errors and uncertainties. This retrieval is free from the plane-parallel homogeneous cloud assumption.