Sensitivity Analyses for the Retrievals of Ice Cloud Properties From Radiometric and Polarimetric Measurements in Sub‐mm/mm and Infrared Bands

Abstract

Simulations of the radiometric and polarimetric properties of ice clouds based on the Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 6 ice cloud model (aggregates in conjunction with the gamma distribution) are performed at wavelengths in the Infrared (IR) and Submillimeter/Millimeter (sub‐mm/mm) regimes. The scattering/absorption/polarization properties from the precalculated database are incorporated into a radiative transfer model, the Atmospheric Radiative Transfer Model (ARTS). A number of sub‐mm/mm bands have been considered from radiometric and polarimetric studies for potential applications to retrieving ice cloud properties at shorter sub‐mm/mm wavelengths (higher frequencies). The IR atmospheric window has also been thoroughly investigated for its feasibility to observe ice clouds. However, in the literature there is a lack of studies utilizing these high frequency bands or polarimetric IR observations to infer ice cloud properties. This study focuses on performing simulations of ice clouds between 680 and 183 GHz (sub‐mm/mm regime) and between 8.6 and 12 μm wavelengths (IR‐window regime) toward determining potential applications to simultaneous retrievals of ice water path (IWP) and effective diameter (Deff) with a primary focus on optically thin cirrus clouds. IWP and Deff isoline plots (lookup tables) are created to conduct sensitivity analyses and to perform preliminary retrievals. Results reveal that the utilization of both sub‐mm/mm and IR wavelengths combined with linearly polarized and unpolarized measurements leads to the most accurate IWP and Deff retrievals with errors lower than 10%.

Evaluation of the impacts of ice cloud vertical inhomogeneity on spaceborne passive submillimeter‐wave simulations

“…Consequently, 1D radiative‐transfer simulation is sufficient in the passive‐only retrieval of column‐integrated properties, for example, ice water path (IWP) and cloud optical thickness (COT), in what can be recognized as one pixel of a cloud scene. For example, lookup tables for the top‐of‐the‐atmosphere brightness temperature differences (BTDs, which could be defined as the brightness temperatures under the clear sky minus that in the cloudy scene) and IWPs, COTs or effective particle sizes could be established at different atmospheric states (Mendrok et al ., 2009; Li et al ., 2017; Coy et al ., 2020). It was found that the retrieved IWPs would be affected by ice clouds' vertically heterogeneous properties.…”

Fast Radiative Transfer Approximating Ice Hydrometeor Orientation and Its Implication on IWP Retrievals

“…The well-established impact of the oriented hydrometeors has encouraged several authors to emphasise the need for the incorporation of hydrometeor orientation into retrievals, based on microwave data [17,19,[21][22][23]. This has not yet occurred.…”