Retrieval of terahertz ice cloud properties from airborne measurements based on the irregularly shaped Voronoi ice scattering models

[摘要] Currently, terahertz remote sensing technology is one ofthe best ways to detect the microphysical properties of ice clouds.Influenced by the representativeness of the ice crystal scattering (ICS)model, the existing terahertz ice cloud remote sensing inversion algorithmsstill have significant uncertainties. In this study, based on the VoronoiICS model, we developed a terahertz remote sensing inversion algorithm ofthe ice water path (IWP) and median mass diameter ( D me ) of ice clouds.This study utilized the single-scattering properties (extinction efficiency,single-scattering albedo, and asymmetry factor) of the Voronoi, sphere, andhexagonal column ICS models in the terahertz region. Combined with 14 408groups of particle size distributions obtained from aircraft-basedmeasurements, we developed the Voronoi, sphere, and column ICS schemes basedon the Voronoi, sphere, and column ICS models. The three schemes were appliedto the radiative transfer model to carry out the sensitivity analysisof the top-of-cloud (TOC) terahertz brightness temperature differencesbetween cloudy and clear skies (BTDs) on the IWP and D me . Thesensitivity results showed that the TOC BTDs between 640 and 874 GHz arefunctions of the IWP, and the TOC BTDs of 380, 640, and 874 GHz arefunctions of the D me . The Voronoi ICS scheme possesses strongersensitivity to the D me than the sphere and column ICS schemes. Based onthe sensitivity results, we built a multi-channel look-up table for BTDs.The IWP and D me were searched from the look-up table using an optimalestimation algorithm. We used 2000 BTD test data randomly generated by theRSTAR model to assess the algorithm's accuracy. Test results showed that thecorrelation coefficients of the retrieved IWP and D me reached 0.99 and0.98, respectively. As an application, we used the inversion algorithm toretrieve the ice cloud IWP and D me based on the Compact Scanning Submillimeter-wave Imaging Radiometer (CoSSIR) airborneterahertz radiation measurements. Validation against the retrievals of theBayesian algorithm reveals that the Voronoi ICS model performs better thanthe sphere and hexagonal column ICS models, with enhancement of the meanabsolute errors of 5.0 % and 12.8 % for IWP and D me , respectively.In summary, the results of this study confirmed the practicality andeffectiveness of the Voronoi ICS model in the terahertz remote sensinginversion of ice cloud microphysical properties.

[学科分类] 内科医学