Wavelength dependence of ice cloud backscatter properties for space-borne polarization lidar applications

Abstract

We investigated the use of backscatter properties of atmospheric ice particles for space-borne lidar applications. We estimated the average backscattering coefficient (β), backscatter color ratio (χ), and depolarization ratio (δ) for ice particles with a wide range of effective radii for five randomly oriented three-dimensional (3D) and three quasi-horizontally oriented two-dimensional (2D) types of ice particle using physical optics and geometrical integral equation methods. This is the first study to estimate the lidar backscattering properties of quasi-horizontally oriented non-pristine ice crystals. We found that the χ–δ relationship was useful for discriminating particle types using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) data. The lidar ratio (S)–δ relationship, which is determined using space-borne high-spectral-resolution lidar products such as EarthCARE ATLID or future space-borne lidar missions, may also produce robust classification of ice particle types because it is complementary to the χ–δ relationship.

Properties of Cirrus Clouds over the European Arctic (Ny-Ålesund, Svalbard)

“…They reported an average CR of 1.1 ± 0.8 over Kuopio, indicating the presence of slightly bigger ice crystals compared to Ny-Ålesund. Finally, according to the simulations of Okamoto et al [33] the CR ranged mainly between 0.7 and 2 (values from Figure 9a of Okamoto et al [33] were inverted to match our definition).…”

“…Specular reflections appear in the presence of horizontally-oriented hexagonal ice crystals and they can be identified by local maxima in the backscatter coefficient together with local minima in the LPDR profiles [32]. According to simulations, the LPDR of horizontally-oriented crystals is lower than 10% (Figures 8b and 9b from Okamoto et al [33]). Accordingly, we identified LPDR profiles with local minima lower than 10% coincident with local maxima in the backscatter coefficient.…”

“…Additionally, cirrus layers with unexpectedly high LR were screened out. Based on the simulations of Okamoto et al [33], apparent LR values (before accounting for the multiplescattering effect) higher than 50 sr are not expected. The exploration of such high values revealed a higher occurrence in spring and for vertically-inhomogeneous layers.…”

Lidar Ratio–Depolarization Ratio Relations of Atmospheric Dust Aerosols: The Super‐Spheroid Model and High Spectral Resolution Lidar Observations

“…High spectral resolution lidar (HSRL) is a powerful technique that can independently measure the extinction and backscatter coefficients of aerosols and clouds, allowing the lidar ratio (defined as the extinction to backscatter ratio) to be obtained (Freudenthaler et al., 2009 ; Hair et al., 2008 ; Jin et al., 2020 ; Liu et al., 2002 ; Mona et al., 2012 ; Sroga et al., 1983 ). The lidar ratio and depolarization ratio relation is used to distinguish aerosol (Burton et al., 2012 ) and ice particle types (Okamoto et al., 2019 , 2020 ). The Earth Cloud, Aerosol, and Radiation Explorer (EarthCARE) satellite is a joint venture between the European Space Agency (ESA) and Japanese Aerospace Exploration Agency (JAXA) scheduled for launch in 2023.…”

Investigations of the corner-reflection effect at soundings of cirrus clouds by a scanning lidar

“…While in the case of randomly oriented crystals the lidar signals don't depend on lidar tilts, in the case of oriented crystals this dependence becomes crucial. Therefore both tilted and scanning lidars are needed for studying the clouds with preferably oriented ice crystals that were explored by a number of authors, for example [19][20][21][22][23][24][25][26][27] .…”